TM

Medical DictionaryThird Edition

From the Doctors and Experts at WebMD

01_189283 ffirs.qxp 4/25/08 6:40 PM Page i

Webster’s New World™ Medical Dictionary, Third Edition

Copyright © 2008 MedicineNet.com. All rights reserved.

Published by Wiley Publishing, Inc., Hoboken, New Jersey

No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or byany means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permittedunder Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to theCopyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978)646-8600, or on the web at www.copyright.com. Requests to the Publisher for permission should beaddressed to the Legal Department, Wiley Publishing, Inc., 10475 Crosspoint Blvd., Indianapolis, IN 46256,(317) 572-3447, fax (317) 572-4355, or online at http://www.wiley.com/go/permissions.

The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation warranties of fitness for a particular purpose. No warranty may be created or extended by sales orpromotional materials. The advice and strategies contained herein may not be suitable for every situation.This work is sold with the understanding that the publisher is not engaged in rendering legal, accounting, orother professional services. If professional assistance is required, the services of a competent professionalperson should be sought. Neither the publisher nor the author shall be liable for damages arising herefrom. The fact that an organization or Website is referred to in this work as a citation and/or a potentialsource of further information does not mean that the author or the publisher endorses the information theorganization or Website may provide or recommendations it may make. Further, readers should be awarethat Internet Websites listed in this work may have changed or disappeared between when this work waswritten and when it is read.

Trademarks: Wiley, the Wiley Publishing logo, Webster’s New World, and all related trademarks, logos andtrade dress are trademarks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates. Allother trademarks are the property of their respective owners. Wiley Publishing, Inc. is not associated withany product or vendor mentioned in this book.

For general information on our other products and services or to obtain technical support, please contactour Customer Care Department within the U.S. at 800-762-2974, outside the U.S. at 317-572-3993, or fax317-572-4002.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may notbe available in electronic books. For more information about Wiley products, please visit our web site atwww.wiley.com.

Library of Congress Cataloging-in-Publication Data is available from the publisher upon request.

ISBN: 978-0-470-18928-3

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

Book production by Wiley Publishing, Inc. Composition Services

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TM

Medical DictionaryThird Edition

From the Doctors and Experts at WebMD

01_189283 ffirs.qxp 4/25/08 6:40 PM Page i

Webster’s New World™ Medical Dictionary, Third Edition

Copyright © 2008 MedicineNet.com. All rights reserved.

Published by Wiley Publishing, Inc., Hoboken, New Jersey

No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or byany means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permittedunder Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to theCopyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978)646-8600, or on the web at www.copyright.com. Requests to the Publisher for permission should beaddressed to the Legal Department, Wiley Publishing, Inc., 10475 Crosspoint Blvd., Indianapolis, IN 46256,(317) 572-3447, fax (317) 572-4355, or online at http://www.wiley.com/go/permissions.

The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation warranties of fitness for a particular purpose. No warranty may be created or extended by sales orpromotional materials. The advice and strategies contained herein may not be suitable for every situation.This work is sold with the understanding that the publisher is not engaged in rendering legal, accounting, orother professional services. If professional assistance is required, the services of a competent professionalperson should be sought. Neither the publisher nor the author shall be liable for damages arising herefrom. The fact that an organization or Website is referred to in this work as a citation and/or a potentialsource of further information does not mean that the author or the publisher endorses the information theorganization or Website may provide or recommendations it may make. Further, readers should be awarethat Internet Websites listed in this work may have changed or disappeared between when this work waswritten and when it is read.

Trademarks: Wiley, the Wiley Publishing logo, Webster’s New World, and all related trademarks, logos andtrade dress are trademarks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates. Allother trademarks are the property of their respective owners. Wiley Publishing, Inc. is not associated withany product or vendor mentioned in this book.

For general information on our other products and services or to obtain technical support, please contactour Customer Care Department within the U.S. at 800-762-2974, outside the U.S. at 317-572-3993, or fax317-572-4002.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may notbe available in electronic books. For more information about Wiley products, please visit our web site atwww.wiley.com.

Library of Congress Cataloging-in-Publication Data is available from the publisher upon request.

ISBN: 978-0-470-18928-3

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

Book production by Wiley Publishing, Inc. Composition Services

01_189283 ffirs.qxp 4/18/08 10:03 PM Page ii

http://www.wiley.com/go/permissions

Acknowledgments

At MedicineNet.com, a part of the WebMD network, we continue to foster the concept that you, thereaders, are truly interested in understanding health issues and medical concepts. Accordingly, wehave addressed the medical terms in this dictionary with sensitivity to potential concerns of thosewho are acutely or chronically confronting disease or health concerns. We are grateful for yourinterest in health topics as it is a driving force for the development of the Webster’s New WorldMedical Dictionary, Third Edition.

On behalf of the MedicineNet.com division of WebMD, we wish to thank the staff at Wiley Publishing,Inc., especially Roxane Cerda and Suzanne Snyder, for bringing this dictionary to those who need it.We also thank the officers of MedicineNet.com, particularly Gene Lu and David Sorenson, who havesupported the development of this dictionary.

The excellence of the technical and editorial staffs at MedicineNet.com greatly facilitated this entireproject. Dan Griffith and Michael Cupp provided the unique publishing software that made it all pos-sible. Cynde Lee, Kelly McKiernan, and Tanya Buchanan have performed magnificently in managingthe vast amount of content and communication between authors and editors. David Sorenson hasbeen an inspirational catalyst for motivation and consistent superior quality.

William C. Shiel, Jr., MD, FACP, FACR, thanks his children, Cara Shiel Krenn, Daniel, and Timothy fortheir support. He also acknowledges the support and encouragement of his parents, William andVirginia Shiel, as well as his dear mother-in-law, Helen Stark. With infinite gratitude and love hethanks his wife, Catherine, for her support, love, and editing. With gratitude he acknowledges theHerculean efforts of Frederick Hecht, MD, FAAP, FACMG in developing previous editions of this dic-tionary. And, with admiration beyond words, he thanks his dear friend, colleague, and co-founderof MedicineNet.com, Dennis Lee, MD.

Melissa Conrad Stöppler, MD wishes to thank her husband, Hubert Stöppler, and her children,Johannes, Anna, and Tilman, for their enduring support, love, and patience. She also gratefullyacknowledges the support and encouragement of her parents, Kathryn B. Conrad and the late HenryE. Conrad, Jr.

Thank you all.

–William C. Shiel, Jr., MD, FACP, FACR

–Melissa Conrad Stöppler, MD

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Editorial StaffCo-Editors-in-ChiefWilliam C. Shiel, Jr., MD, FACP, FACRwww.MedicineNet.com

Melissa Conrad Stöppler, MDwww.MedicineNet.com

Assistant EditorsDennis Lee, MDwww.MedicineNet.com

Jay W. Marks, MDwww.MedicineNet.com

Ruchi Mathur, MD, FRCP(C)www.MedicineNet.com

Content ManagersCynde LeeKelly McKiernanwww.MedicineNet.com

Concept DevelopmentDavid SorensonGene Luwww.MedicineNet.com

Get Additional Free Content Online

As an added bonus to this fully revised third edition of the Webster’s New World™ Medical Dictionary,you can visit the companion website at www.medterms.com/wnw.

You’ll find a free PDF Healthcare Guide to help you get the most out of your personal medical care.You can also listen to podcasts from Dr. William Shiel and Dr. Melissa Stöppler, the co-editors of theWebster’s New World Medical Dictionary, in which they discuss strategies to help you better com-municate with your doctors and caregivers.

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About the Authors

William C. Shiel, Jr., MD, FACP, FACR, Co-Editor-in-Chief

William C. Shiel, Jr., MD, FACP, FACR, received a bache-lor of science degree with honors from the University ofNotre Dame. There he was involved in research in radi-ation biology and received the Huisking Scholarship.After graduating from St. Louis University School ofMedicine, he completed his internal medicine resi-dency and rheumatology fellowship at University ofCalifornia, Irvine. He is board certified in internal med-icine and rheumatology and is a fellow of the AmericanColleges of Physicians and Rheumatology. Dr. Shiel is inactive practice in the field of rheumatology at theArthritis Center of Southern Orange County, California.He is currently an active associate clinical professor ofmedicine at University of California, Irvine. He has

served as chair of the Department of Internal Medicine at Mission Hospital Regional Medical Centerin Mission Viejo, California. Dr. Shiel has authored numerous articles on subjects related to arthri-tis for prestigious peer-reviewed medical journals, as well as many expert medical-legal reviews. Hehas lectured in person and on television both for physicians and the community. He is a contribu-tor for questions for the American Board of Internal Medicine and has reviewed board questions onbehalf of the American Board of Rheumatology Subspecialty. He served on the Medical and ScientificCommittee of the Arthritis Foundation, and he is currently on the Medical Advisory Board of LupusInternational. Dr. Shiel is proud to have served as chief editor for MedicineNet.com since its found-ing in 1996. He was co-editor-in-chief of the first and second editions of Webster’s New WorldMedical Dictionary.

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Melissa Conrad Stöppler, MD, Co-Editor-in-Chief

Melissa Conrad Stöppler, MD, is a US board-certifiedanatomic pathologist with subspecialty training in thefields of experimental and molecular pathology. Dr.Stöppler’s educational background includes a BA withHighest Distinction from the University of Virginia andan MD from the University of North Carolina. She com-pleted residency training in anatomic pathology atGeorgetown University followed by subspecialty fellow-ship training in molecular diagnostics and experimen-tal pathology. Dr. Stöppler served as a faculty memberof the Georgetown University School of Medicine andhas also served on the medical faculty at the Universityof Marburg, Germany. Her research in the area of virus-induced cancers has been funded by the National

Institutes of Health as well as by private foundations. She has a broad list of medical publications,abstracts, and conference presentations and has taught medical students and residents both in theUnited States and Germany. Dr. Stöppler was named a fellow of the Alexander von Humboldt Societyin Germany and was a recipient of a Physician Scientist Award from the US National Cancer Institute.Dr. Stöppler currently serves on the Medical Editorial Board of MedicineNet.com, and is the ChiefMedical Editor of eMedicineHealth.com, both WebMD Inc. companies. Her experience also includestranslation and editing of medical texts in German and English. Dr. Stöppler’s special interests inmedicine include family health and fitness, patient education/empowerment, and molecular diag-nostic pathology. She currently resides in the San Francisco Bay area with her husband and theirthree children.

Dennis Lee, MD, Assistant Editor

Dennis Lee, MD, was born in Shanghai, China, and received his college and medical training in theUnited States. He is fluent in English and three Chinese dialects. He graduated with chemistry depart-mental honors from Harvey Mudd College. He was appointed president of AOA society at UCLASchool of Medicine. He underwent internal medicine residency and gastroenterology fellowshiptraining at Cedars-Sinai Medical Center. Board certified in internal medicine and gastroenterology,Dr. Lee is currently a member of Mission Internal Medical Group, a multispecialty medical groupserving southern Orange County, California. Dr. Lee has maintained an interest in technology andmedical education. He is a regular guest lecturer at Saddleback College in Orange County, California.Dr. Lee serves as chair of MedicineNet.com.

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Jay W. Marks, MD, Assistant Editor

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from YaleUniversity School of Medicine and trained in internal medicine and gastroenterology atUCLA/Cedars-Sinai Medical Center in Los Angeles. For 20 years he was associate director of theDivision of Gastroenterology at Cedars-Sinai Medical Center and an associate professor of medicine,in residence, at UCLA. At Cedars-Sinai he co-directed the Gastrointestinal Endoscopy Unit, taughtphysicians during their graduate and postgraduate training, and performed specialized, nonendo-scopic gastrointestinal testing. He carried out Public Health Service–sponsored (National Institutesof Health) clinical and basic research into mechanisms of the formation of gallstones and methodsfor the nonsurgical treatment of gallstones. He is the author of 36 original research manuscripts and24 book chapters. Dr. Marks presently directs an independent gastrointestinal diagnostic unit wherehe continues to perform specialized tests for the diagnosis of gastrointestinal diseases. Dr. Marksserves as medical and pharmacy editor of MedicineNet.com.

Ruchi Mathur, MD, FRCP(C), Assistant Editor

Dr. Mathur received her medical degree in Canada and did her medical residency at the Universityof Manitoba in Internal Medicine. Dr. Mathur is a certified fellow of the Royal College of Physiciansof Canada and is US board certified in internal medicine and endocrinology, diabetes and metabo-lism. She has been the recipient of numerous research grants which have included the AmericanDiabetes Association grant for research in the field of diabetes and gastric dysmotility and theEndocrine Fellows Foundation Grant for Clinical Research. She has an extensive list of medical pub-lications, abstracts, and posters and has given numerous lectures on diabetes. Most recently she hasco-authored the textbook Davidson’s Diabetes Mellitus: Diagnosis and Treatment, published byElsevier. Dr. Mathur has also served as Research Fellow at Cedars-Sinai Medical Center and a clini-cal instructor at UCLA in endocrinology and metabolism. Currently Dr. Mathur is Co-Director of theDiabetes Management Clinic at the Roybal Comprehensive Health Center and Assistant Professor ofMedicine at the Keck School of Medicine, University of Southern California.

Contributing Authors

Ronald Adamany, MD, Gastroenterology • Kent Adamson, MD, Orthopedic Surgery • Leon Baginski,MD, Obstetrics & Gynecology • Jerry Balentine, DO, FACOEP, FACEP, Emergency Medicine • EdwardBlock, MD, Gastroenterology • James Bredencamp, MD, Otolaryngology • Yuri Bronstein, MD,Neurology • Rudolph Brutico, MD, Pediatrics • Carolyn Janet Crandall, MD, Internal Medicine &Women’s Health • Howard Crystal, MD, Neurology • John Cunha, DO, Emergency Medicine • EricDaar, MD, Internal Medicine & Infectious Diseases • Andrew A. Dahl, MD, FACS, Opthamology •

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Fernando Dangond, MD, Neurology • Charles C.P. Davis, MD, PhD, Emergency Medicine • RoxanneDryden-Edwards, MD, Psychiatry and Mental Health • Jason C. Eck, DO, MS, Orthopaedic Surgery • Steve Ehrlich, MD, Cardiology • Manuel Fernandez, MD, Endocrinology • Robert Ferry, MD,Pediatric Endocrinologist • Michael C. Fishbein, MD, Cardiovascular & Autopsy Pathology • Tse-LingFong, MD, Hepatology • Catherine G. Fuller, MD, Allergy & Immunology • Ronald Gehling, MD,Allergy & Immunolgy • Gus Gialamas, MD, Orthopedic Surgery • Gary W. Gibbon, MD, PulmonaryDisease & Allergy • Mitchell J. Gitkind, MD, Gastroenterology • Vay Liang W. Go, MD, Nutrition •Sandra Gonzalez Gompf, MD, FACP, FIDSA, Infectious Disease • Jayson Goo, ATC, MA, CKTI, HumanPerformance/Corrective Therapy • Daniel L. Gomel, MD, Internal Medicine & Geriatrics • MarkGraber, MD, Family Practice • Harold H. Harsch, MD, Psychiatry • Roza Hayduk, MD, SleepMedicine • Barbara K. Hecht, PhD • Frederick Hecht, MD, FAAP • Standiford Helm III, MD,Anesthesiologist/Pain Management • Kendall Ho, MD, Emergency Medicine • Debra E. Houry, MD,MPH, Emergency Medicine/Women’s Health • Camille Marie Teres Hylton, MD, Ophthamology •David Kaminstein, MD, Gastroenterology • Kenneth Kaye, MD, Pathology • Jillyen E. Kibby, M.A.,CCC-A, Audiology • Harley J. Kornblum, MD, Pediatrics & Neurology • Betty Kovacs, MS, RD,Nutrition • Daniel Lee Kulick, MD, FACC, FSCAI., Internal Medicine & Cardiology • Eric Lee, MD,Gastroenterology • Margaret Lee, DDS, Dentistry • Stacy E. Lee, MD, Allergy & Immunology •Michael Lill, MD, Hematology/Oncology • Arthur H. Loussararian, MD, Inetrnal Medicine &Cardiology • Ralph Maeda, MD, Surgery • Dwight Makoff, MD, Nephrology & Hypertension •Murray Margolis, MD, Internal Medicine • Randy Martin, MD, Pulmonary/Infectious Diseases •James Meaglia, MD, Urology • John Mersch, MD, Pediatrics • Michael Miyamoto, MD, Cardiology • Zab Mohsenifar, MD, Internal Medicine & Pulmonary Diseases • John R. Morris, MD, OrthopedicSurgery • Mim Mulford, MD, Endocrinology • Marty Nettleman, MD, MS, Infectious Disease • MarkScott Noah, MD, Internal Medicine • Omudhome Ogbru, PharmD, Pharmacy • Peter J. Panzarino,Jr. MD, Psychiatry & Behavioral Medicine • David Adam Perlstein, MD, FAAP, Pediatarics • DennisPhilips, MD, Pediatrics • Donald Pratt, MD, Internal Medicine • Stefan M. Pulst, MD, Neurology •J. Bradley Randleman, MD, Opthamology • Donald Rediker, MD, Cardiology • Alan Rockoff, MD,Dermatology • Emmanuel Saltiel, PharmD FASHP, FCCP, Pharmacy • Stephen J. Sanders, M.A., CCC-A,Audiology • Michael Santoro, MD, Gastroenterology • George Schiffman, MD, Pulmonary • LeslieJ. Schoenfield, MD, PhD • Melvin Shiffman, MD, Cosmetic Surgery • Lawrence J. Schwartz, MD,Ophthalmology • Joseph Sciammarella, MD, FACP, FA.CEP, Emergency Medicine • John Sheppard,MD, Ophthalmology and Pharmacology • David Simon, MD, Internal Medicine • Robert Simon, MD,Neurology • Thomas P. Sokol, MD, FACS, FASCRS, Gastroenterology • Mark Sullivan, MD, Urology •Alan Szeftel, MD, Allergy and Immunology/Pulmonary Disease • Bruce Tammelin, MD, PulmonaryDisease • Suzanne Trupin MD, FACOG, Obstetrics and Gynecology • Michael Truong, MD,Endocrinology • Theodore Van Dam, MD, Internal Medicine • John Vierling, MD, Hepatology •Benjamin C. Wedro, MD, FAAEM, Emergency Medicine • Richard Weil, M.Ed., CDE, ExercisePhysiology, Diabetes Educator • Maureen Welker, MSN, NPc, CCRN • Edward J. White, MD, GeneralSurgery • Leslie Williams, EdD, Psychology • Joseph Y. Wu, MD, Internal Medicine & Geriatrics •Marilyn A.D. Yee, PharmD, Pharmacy • David Zachary, MD, Family Medicine

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Introduction

lexicographer A writer of dictionaries, a harmless drudge.

–Samuel Johnson, 1755

Like the previous editions, this edition has been conceived and developed by the staff of the healthinformation Web site MedicineNet.com, part of the WebMD Health Network. One of the earliesthealth information sites on the Internet, MedicineNet.com has devoted a number of years to creat-ing an online medical dictionary that now contains a wealth of contemporary medical terms andprovides the broad foundation for this book.

To create this new edition of Webster’s New World Medical Dictionary, we have reviewed everyentry in the previous edition and have rewritten and strengthened many of those entries. In addition,we have selected new entries from our online medical dictionary for incorporation into this thirdedition. A unique feature of an online medical dictionary is that it can (and does) evolve rapidly tokeep pace with the changes in medicine. We have taken advantage of this to update Webster’s NewWorld Medical Dictionary.

Like all of the medical content from MedicineNet.com, this dictionary was written and edited byphysicians, to be used by anyone and everyone concerned about their own health or the health ofthose who matter to them. All the medical information found on MedicineNet.com has been devel-oped by a network of physicians. The physicians select the topics and review and edit all written con-tent. These physicians also make use of medical specialists and health writers throughout the US.The “About the Authors” pages provide abbreviated biographies of the editors and specialists whocontributed content to the MedicineNet.com online dictionary and this book.

Medicine is now advancing with remarkable rapidity on many fronts, and the language of medi-cine is also continually evolving with remarkable rapidity, commensurate with the changes. Today,there is constant need for communication between and among consumers and providers of healthcare. There is consequently a need for a high-quality, contemporary medical dictionary.

In the current health care environment, patients and their physicians, nurses, and allied health pro-fessionals must be able to discuss the ever-changing aspects of health, disease, and biotechnology.An accurate understanding of medical terminology can assist communication and improve care forpatients, and it can help to alleviate the concerns of family members and friends.

The fact that the content of this dictionary is physician-produced by MedicineNet.com ensures anunusual degree of professional expertise, reliability, and perspective.

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As a bonus, this edition includes a companion Web site at www.medterms.com/wnw. There you willfind content not found in the book such as PDF healthcare guides and audio podcasts.

We hope that you will find Webster’s New World Medical Dictionary, Third Edition a valuable addi-tion to your family or office library and a source of both information and illumination in any med-ical situation.

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A In genetics, adenine, a member of the adenine-thymine (A-T) base pair in DNA.

a- Prefix indicating the absence or depletion ofsomething: for example, aphagia (not eating) oraphonia (voiceless). The related prefix an- is usu-ally used before a vowel, as in anemia (withoutblood) and anoxia (without oxygen).

AA 1 Alcoholics Anonymous. 2 Amino acid.

AAAS American Association for the Advancementof Science, a professional organization that pub-lishes the weekly journal Science.

AAFP 1 American Association of FamilyPhysicians, a professional organization for physi-cians who treat both children and adults. 2American Academy of Family Physicians, a profes-sional organization for physicians who treat bothchildren and adults.

AAO 1 American Association of Ophthalmology, aprofessional organization. 2 American Associationof Orthodontists, a professional organization. 3American Academy of Otolaryngology, a professionalorganization.

AAOS American Academy of OrthopaedicSurgeons, a professional organization. See alsoorthopaedics.

AAP 1 American Academy of Pediatrics, a profes-sional organization for physicians who treat infants, children, adolescents, and young adults.2 American Academy of Pedodontics, a professionalorganization. 3 American Academy ofPeriodontology, a professional organization. 4American Association of Pathologists, a professionalorganization.

ab- Prefix indicating from, away from, or off, as inabduction (movement of a limb away from the mid-line of the body) and abnormal (away from normal).

abdomen The part of the body that contains allthe structures between the chest and the pelvis. Theabdomen, or belly, is anatomically separated fromthe chest by the diaphragm, the powerful muscle

that spans the body cavity, just below the lungs. Seealso abdominal cavity.

abdomen, acute See acute abdomen.

abdominal aorta The final section of the aorta,the largest artery in the body, which begins at thediaphragm as a continuation of the thoracic aortaand ends by splitting in two, to form the commoniliac arteries. The abdominal aorta supplies oxy-genated blood to all the abdominal and pelvicorgans, as well as to the legs. See also aorta.

abdominal aortic aneurysm See aneurysm,abdominal aortic.

abdominal cavity The cavity within theabdomen. This space between the abdominal walland the spine contains a number of crucial organs,including the lower part of the esophagus, the stom-ach, small intestine, colon, rectum, liver, gallblad-der, pancreas, spleen, kidneys, adrenal glands,ureters, and bladder. See also abdomen.

abdominal guarding Tensing of the abdominalwall muscles to guard inflamed organs within theabdomen from the pain of pressure upon them.Abdominal guarding is detected when the abdomenis pressed and is an indication that inflammation ofthe inner abdominal (peritoneal) surface may bepresent due, for example, to appendicitis or diverti-culitis. The tensed muscles of the abdominal wallautomatically go into spasm to keep the tenderunderlying tissues from being irritated.

abdominal hysterectomy See hysterectomy,abdominal.

abdominal muscle One of a large group of mus-cles in the front of the abdomen that assists in main-taining regular breathing movements, supports themuscles of the spine while lifting, and keeps abdom-inal organs in place. Abdominal muscles are the tar-get of many exercises, such as sit-ups. Abdominalmuscles are informally known as the abs.

abdominal pain Pain in the belly. Abdominalpain can be acute or chronic. It may reflect a majorproblem with one of the organs in the abdomen,such as appendicitis or a perforated intestine, or itmay result from a fairly minor problem, such asexcess buildup of intestinal gas.

abducens nerve See abducent nerve.

abducent nerve The sixth cranial nerve, whichemerges from the skull to operate the lateral rectusmuscle. This muscle draws the eye toward the sideof the head. Paralysis of the abducent nerve causesinward turning of the eye.

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abduction The movement of a limb away fromthe midline of the body. The opposite of abductionis adduction.

abductor muscle See muscle, abductor.

ABG Arterial blood gas, a sampling of the bloodlevels of oxygen and carbon dioxide within thearteries, as opposed to the levels of oxygen and car-bon dioxide in veins. Typically, the acidity (pH) isalso simultaneously measured.

abiotrophy Loss of function, or degeneration forreasons unknown.

ablate To remove, from a Latin word meaning “tocarry away.” See ablation.

ablation Removal or excision. Ablation is usuallycarried out surgically. For example, surgicalremoval of the thyroid gland (a total thyroidectomy)is ablation of the thyroid.

abnormal Outside the expected norm, oruncharacteristic of a particular patient.

ABO blood group The major human bloodgroup system. The ABO type of a person depends onthe presence or absence of two genes, A and B.These genes determine the configuration of the redblood cell surface. A person who has two A geneshas red blood cells of type A. A person who has twoB genes has red cells of type B. If the person has oneA and one B gene, the red cells are type AB. If theperson has neither the A nor the B gene, the redcells are type O. It is essential to match the ABO sta-tus of both donor and recipient in blood transfu-sions and organ transplants.

abortifacient A medication or substance thatcauses pregnancy to end prematurely.

abortion Premature exit of the products of thefetus, fetal membranes, and placenta from theuterus. Abortion can be a natural process, as in amiscarriage; an induced procedure, using medica-tion or other substances that cause the body toexpel the fetus; or a surgical procedure thatremoves the contents of the uterus. See also dila-tion and curettage.

abortion, habitual The miscarriage of three ormore consecutive pregnancies with no interveningpregnancies. Habitual abortion is a form of infertil-ity. Also known as recurrent abortion and multipleabortion.

abortion, multiple See abortion, habitual.

abortion, recurrent See abortion, habitual.

abortion, spontaneous Miscarriage.

abortive Tending to cut short the course of a dis-ease, as in abortive polio (polio cut short).

abortive polio A minor, abbreviated form ofinfection with the polio virus. Full recovery occursin 24 to 72 hours, and the condition does notinvolve the nervous system or permanent disabili-ties. See also polio.

ABP American Board of Pediatrics, a professionalorganization for physicians who treat infants, chil-dren, adolescents, and young adults.

abrasion 1 A wearing away of the upper layer ofskin as a result of applied friction force. See alsoscrape. 2 In dentistry, the wearing away of a toothsurface.

abruptio placentae Premature separation(abruption) of the placenta from the wall of theuterus, often in association with high blood pres-sure or preeclampsia. Abruption is a potentiallyserious problem both for mother and fetus becausethe area where it occurs bleeds and the uterusbegins to contract. Shock may result. See also pla-centa; preeclampsia.

abs Slang term for the abdominal muscles.

abscess A local accumulation of pus anywhere inthe body. See also boil; pus.

abscess, perianal An abscess next to the anusthat causes tenderness, swelling, and pain on defe-cation.

abscess, peritonsillar An abscess behind thetonsils that pushes one of the tonsils toward theuvula (the prominent soft tissue dangling from theback of the palate in the back of the mouth). A peri-tonsillar abscess is generally very painful and asso-ciated with difficulty opening the mouth. If aperitonsillar abscess is untreated, the infection canspread deep into the neck, causing airway obstruc-tion and other life-threatening complications.

abscess, skin A confined collection of pus in theskin. The common boil is a type of skin abscess. Seealso boil.

abscission To remove tissue by cutting it away, asin surgery. See also resection.

absence of the breast See amastia.

absence of the nipple See athelia.

abduction 2

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absinthe An emerald-green liqueur flavored withextracts of the wormwood plant, licorice, and aro-matic flavorings in an alcohol base. Absinthe wasmanufactured, commercialized, and popularized inFrance in the late 1700s. It was an extremely addic-tive drink. Prolonged drinking of absinthe causesconvulsions, blindness, hallucinations, and mentaldeterioration. Absinthe has been banned, but some-thing of its taste is still available in such drinks asGreek ouzo and French pastis. Homemade absinthemay still be illicitly consumed in some areas.

absolute CD4 count The number of “helper” T-lymphocytes in a cubic millimeter of blood. Theabsolute CD4 count is frequently used to monitorthe extent of immune suppression in persons withHIV because with HIV, this number declines as theinfection progresses. Also known as T4 count.

absorption Uptake. For example, intestinalabsorption is the uptake of food (or other sub-stances) from the digestive tract.

abstinence The voluntary self-denial of food,drink, or sex. Today, abstinence most commonlyrefers to denial of one’s sexual activity.

abuse, child See child abuse.

abuse, elder See elder abuse.

a.c. Abbreviation of the Latin phrase ante cibum,meaning “before meals.” See also Appendix A,“Prescription Abbreviations.”

AC joint See acromioclavicular joint.

acanthosis nigricans A skin condition charac-terized by dark, thickened, velvety patches, espe-cially in the folds of skin in the armpit, groin, andback of the neck. It can occur with endocrine dis-eases such as Cushing disease and diabetes mellitus,from tumors of the pituitary gland, underlying malig-nancies, certain drugs, and as a genetic disorder. Itis most common in people who have insulin resist-ance—those whose body is not responding cor-rectly to the insulin that they make in their pancreas.

acapnia Lower than normal level of carbon dioxidein the blood. The opposite of acapnia is hypercapnia.

accelerated phase of leukemia Chronic myel-ogenous leukemia that is progressing. In this phase,the number of immature, abnormal white bloodcells in the bone marrow and blood is higher thanin the chronic phase, but not as high as in the blastphase.

accessory nerve The eleventh cranial nerve,which emerges from the skull and receives an addi-tional (accessory) root from the upper part of thespinal cord. It supplies the sternocleidomastoid andtrapezius muscles.

accessory neuropathy A disease of the acces-sory nerve, paralysis of which prevents rotation ofthe head away from one or both sides and causesthe shoulder to droop. Damage can be confined tothe accessory nerve, or it may also involve the ninthand tenth cranial nerves, which exit the skullthrough the same opening.

accessory placenta See placenta, accessory.

acclimatization to altitude The process ofadapting to the decrease in oxygen concentration ata specific altitude. A number of changes must takeplace for the body to operate with decreased oxy-gen. These changes include increasing the depth ofrespiration; increasing the pressure in the pul-monary arteries, forcing blood into portions of thelung that are normally not used at sea level; manu-facturing additional oxygen-carrying red bloodcells; and manufacturing extra 2, 4-DPG, a sub-stance that facilitates the release of oxygen fromhemoglobin to the body tissues. Acclimatizationgenerally takes 1 to 3 days and occurs after anysignificant altitude change above 1,220 meters(approximately 4,000 feet). Acclimatization is thebody’s natural means of correcting altitude sicknessand the rate of acclimatization depends on the alti-tude, rate of ascent, and individual susceptibility.

accoucheur A male obstetrician. Anaccoucheuse is a woman obstetrician, or sometimesa midwife.

ACE Angiotensin converting enzyme. ACE convertsan angiotensin to its activated form, angiotensin II,enabling it to function. Angiotensin II constrictsblood vessels and elevates blood pressure.

ACE inhibitor A drug that inhibits ACE. Using anACE inhibitor relaxes the arteries, not only loweringblood pressure but also improving the pumping effi-ciency of a failing heart and improving cardiac out-put in patients with heart failure. ACE inhibitors aretherefore used for blood pressure control and con-gestive heart failure. ACE inhibitors includebenazepril (brand name: Lotensin), captopril(brand name: Capoten), lisinopril (brand names:Zestril, Prinivil), quinapril (brand name: Accupril),and ramipril (brand name: Altace). Interestingly,ACE inhibitors were originally developed from thevenom of a Brazilian viper snake.

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acentric chromosome A chromosome that islacking a centromere (a specialized region of thechromosome to which spindle fibers attach duringcell division). As a result, an acentric chromosomeis lost when the cell divides. See also centromere.

aceruloplasminemia See ceruloplasmin deficiency.

acetabulum The cup-shaped socket of the hipjoint. The acetabulum is a feature of the pelvis. Thehead (upper end) of the femur (thighbone) fits intothe acetabulum and articulates with it, forming aball-and-socket joint.

acetaminophen A nonaspirin pain reliever oranalgesic. Acetaminophen may be given alone torelieve pain and inflammation or it may be com-bined with other drugs, as in some migraine med-ications, which contain acetaminophen, abarbiturate, and caffeine.

acetone A volatile liquid used as an industrialsolvent. Acetone is also one of the ketone bodiesthat is formed when the body uses fat instead of glu-cose (sugar) for energy. The formation of acetone isusually a sign that cells lack insulin or cannot effec-tively use the insulin that is available, as occurs indiabetes. Acetone is excreted from the body in theurine.

acetone breath The breath of a person withexcessive acetone in their body. Acetone breathsmells fruity and is a telltale sign of significant dia-betes. See also diabetes mellitus.

acetylcholine A neurotransmitter released bynerves that is essential for communication betweenthe nerves and muscles.

acetylsalicylic acid See aspirin.

achalasia A disease of the esophagus that mainlyaffects young adults. Abnormal function of nervesand muscles of the esophagus causes difficulty swal-lowing and sometimes chest pain. Regurgitation ofundigested food can occur, as can coughing orbreathing problems related to entry of food materialinto the lungs. The underlying problems are weak-ness of the lower portion of the esophagus and fail-ure of the lower esophageal sphincter to open andallow passage of food. Diagnosis is made by an X-ray, endoscopy, or esophageal manometry.Treatment includes medication, dilation (stretch-ing) to widen the lower part of the esophagus, andsurgery to open the lower esophagus. A fairly recentapproach involves injecting medicines into thelower esophagus to relax the sphincter.

Achilles tendon One of the longest tendons inthe body, a tough sinew that attaches the calf muscleto the back of the heel bone (calcaneus). The namecomes from Greek mythology: The hero Achilleswas invulnerable to injury except for his heel, whichproved his downfall when it was pierced by Paris’sarrow. It has also proved, literally, to be the down-fall of many athletes who have experienced the sud-den pain of its rupture.

Achilles tendonitis Inflammation in the tendonof the calf muscle, where it attaches to the heelbone. Achilles tendonitis causes pain and stiffness atthe back of the leg, near the heel. Achilles tendonitiscan be caused by overuse of the Achilles tendon,overly tight calf muscles or Achilles tendons, excessuphill running, a sudden increase in the intensity oftraining or the type of shoes worn to run, or wearinghigh heels at work and then switching to a lower-heeled workout shoe. Achilles tendonitis causespain, tenderness, and often swelling over the Achillestendon. There is pain on rising up on the toes andpain with stretching of the tendon. The range ofmotion of the ankle may be limited. Treatmentincludes applying ice packs to the Achilles tendon,raising the lower leg, and taking an anti-inflamma-tory medication. In some severe cases of Achillestendonitis, a cast may be needed for several weeks.A heel lift insert may also be used in shoes to preventfuture overstretching of the Achilles tendon. Exertingrapid stress on the Achilles tendon when it isinflamed can result in rupture of the tendon.

achlorhydria A lack of hydrochloric acid in thedigestive juices in the stomach.

achondroplasia A genetic disorder of bonegrowth and the most common cause of short staturewith disproportionately short arms and legs (knownas dwarfism). The individual has a large head witha prominent forehead (frontal bossing); underde-velopment (hypoplasia) of the midface, with cheek-bones that lack prominence; and a low nasal bridgewith narrow nasal passages. The fingers are short,and the ring and middle fingers diverge to give thehand a trident (three-pronged) appearance. Thebrain is entirely normal in people with achon-droplasia, but complications can damage the brainand spinal cord. Achondroplasia is an autosomaldominant trait, affecting boys and girls equally. Mostcases are due to new gene mutations that appear forthe first time in the affected child. Achondroplasia iscaused by mutation in the fibroblast growth factorreceptor-3 gene (FGFR3), and prenatal diagnosis ispossible. See also dwarfism; dwarfism, hydro-chondroplastic.

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acid, pantothenic Vitamin B5. See alsoAppendix C, “Vitamins.”

acid indigestion Excessive secretion ofhydrochloric acid by the stomach cells. Medicallyknown as hyperchlorhydria. Sometimes used inter-changeably with heartburn. See also heartburn.

acid phosphatase An enzyme that acts to liber-ate phosphate under acidic conditions and is madein the liver, spleen, bone marrow, and prostategland. Abnormally high serum levels of acid phos-phatase may indicate infection, injury, or cancer ofthe prostate.

acidophilus Bacteria found in yogurt with “livecultures” that can help restore supportive bacteriato an intestinal tract whose normal bacterial popu-lation (flora) has been disturbed by disease orantibiotics. Eating yogurt with acidophilus may alsobe useful in preventing overgrowth of yeast(Candida) in the intestinal tract, mouth (thrush),and vagina. See also probiotic.

acidosis Too much acid in the blood and body.Acidosis is an abnormal condition resulting fromthe accumulation of acid or the depletion of alkalinereserves. The pH of a body with acidosis is belownormal. For a person with diabetes, this can lead todiabetic ketoacidosis. The opposite of acidosis isalkalosis. See also pH.

ACL Anterior cruciate ligament.

acne Localized skin inflammation resulting fromoveractivity of the oil glands at the base of hair folli-cles or as a response to contact with irritating sub-stances. See also acne vulgaris.

acne rosacea See rosacea.

acne vulgaris The common form of acne, inteens and young adults, that is due to overactivity ofthe oil (sebaceous) glands in the skin that becomeplugged and inflamed. Acne typically develops whenthe oil glands come to life around puberty and arestimulated by male hormones that are produced inthe adrenal glands of both boys and girls.Treatments include keeping the skin clean andavoiding irritating soaps, foods, drinks, and cosmet-ics. Severe acne and acne in those who are prone toscarring can be treated with topical creams and oralmedications. Skin damaged by acne can beimproved with treatment by a dermatologist orfacial technologist using dermabrasion (sanding),removal of scar tissue via laser, and chemical peels.Also known as pimples.

ACOG American College of Obstetricians andGynecologists, a professional organization forwomen’s health care providers that also does advo-cacy work to improve the care of female patients.

acoustic nerve The eighth cranial nerve which isconcerned with hearing, balance, and head posi-tion. It branches into two parts—a cochlear partthat transmits sound reception for hearing and avestibular part that senses balance and head posi-tion. Also known as the vestibulocochlear nerve.

acquired Not inherited, or present at birth (con-genital), but developing after birth. For example,AIDS is an acquired, not an inherited, form ofimmune deficiency.

acquired immunodeficiency disease SeeAIDS.

acquired mutation A genetic change that occursin a single cell after the conception of an individual.That change is then passed along to all cellsdescended from that cell. Acquired mutations areinvolved in the development of cancer.

acral-lentiginous melanoma See melanoma,acral-lentiginous.

acrocentric chromosome A chromosome inwhich the centromere is located quite near one endof the chromosome. Humans normally have fivepairs of acrocentric chromosomes. Down syndromeis caused by an extra acrocentric chromosome(chromosome 21).

acrocephalosyndactyly An inherited disordercharacterized by abnormalities of the skull, face,hands, and feet. It begins with premature closure ofsome sutures of the skull (craniosynostosis) andresults in a tall peaked head, shallow eye sockets,and underdeveloped cheekbones. With acro-cephalosyndactyly, fingers and toes are fused (syn-dactyly), and the thumbs and big toes have broadends. Acrocephalosyndactyly is an autosomal domi-nant trait that affects boys and girls. A parent cantransmit the gene for the disorder, or it can occurdue to a new mutation. Surgery is often useful tocorrect the abnormalities of the skull, face, hands,and feet. See also Apert syndrome; Crouzon syndrome.

acrochordon See skin tag.

acrocyanosis Blueness of the hands and feet,usually due to inadequate circulation.

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acrodermatitis enteropathica A progressive,hereditary disease of children, characterized by thesimultaneous occurrence of skin inflammation(dermatitis) and diarrhea. The skin on the cheeks,elbows, and knees is inflamed, as is tissue about themouth and anus. There is also balding of the scalp,eyebrows, and lashes; delayed wound healing; andrecurrent bacterial and fungal infections due toimmune deficiency. The key laboratory finding is anabnormally low blood zinc level, reflecting impairedzinc uptake. Treatment with zinc by mouth is cura-tive. Acrodermatitis enteropathica is an autosomalrecessive disorder. See also deficiency, zinc; zinc.

acromegaly See gigantism, pituitary.

acromioclavicular joint A gliding joint locatedbetween the acromion (a projection of the scapulathat forms the point of the shoulder) and the clavi-cle (the collar bone). It is served and supported bythe capsular, superior, and inferior acromioclavicu-lar ligaments; the articular disk; and the coraco-clavicular (trapezoid and conoid) ligaments.Abbreviated AC joint.

acrosyndactyly A condition in which a personhas fused or webbed fingers or toes. Acrosyndactylycan be partial or complete, and it can usually becorrected via surgery. It is associated with severalbirth defect syndromes. See also Apert syndrome.

ACS American College of Surgeons, a professionalorganization that administers standards of practicefor surgeons. Those who meet the group’s standardscan call themselves Fellows of the ACS.

actinic Referring to the ultraviolet (UV) rays fromsunlight and UV lamps. Sunburn is an actinic burn.An actinic keratosis is a skin lesion that is the con-sequence of chronic sun exposure.

actinic keratosis Rough, scaly patches of skinthat are considered precancerous and are due tosun exposure. Prevention is to cut sun exposure andwear sunscreen. Treatments include performingcryosurgery (freezing with liquid nitrogen), cuttingthe keratoses away, burning them, putting 5-fluo-rouracil on them, and using photodynamic therapy(injecting into the bloodstream a chemical that col-lects in actinic keratoses and makes them more sen-sitive to destruction by a specialized form of light).Also known as solar keratosis and senile keratosis.

activated charcoal Charcoal that has beenheated to increase its ability to absorb molecules.Activated charcoal is used to help relieve intestinalgas. It is also used to filter and purify liquids, toabsorb poisons (as in gas mask filters), and in emer-gency situations to neutralize swallowed poisons.

active euthanasia The active acceleration of aterminally ill patient’s death by use of drugs or othermeans. Currently, active euthanasia is openly prac-ticed in the Netherlands and in the US state ofOregon. The patient’s request to the physician mustbe voluntary, explicit, and carefully considered, andit must be made repeatedly. Moreover, the patient’ssuffering must be unbearable and without anyprospect of improvement. Suicide for other rea-sons, whether irrational or rational, is not activeeuthanasia. The forced killing of an ill or disabledperson, as has occurred in eugenics programs, isalso not active euthanasia. And although medica-tions administered for pain relief may hasten death,aggressive pain relief is a normal medical decisionin terminal care, not in active euthanasia. See alsoassisted suicide; eugenics; euthanasia.

active immunity Immunity produced by thebody in response to stimulation by a disease-caus-ing organism or other agent.

activities of daily living Things that a personnormally does during a day, including self-care(eating, bathing, dressing, grooming), work, home-making, and leisure. The ability or inability to per-form these activities can be used as a practicalmeasure of ability or disability, and it may be usedby insurers and HMOs as a rationale for approvingor denying physical therapy or other treatments.Abbreviated ADL.

acuity, auditory The clearness of hearing, ameasure of how well a person hears.

acuity, visual The clearness of vision, a measureof how well one sees.

acuity test, visual The familiar eye chart test,which measures how well a person can see at vari-ous distances.

acupressure The application of pressure on spe-cific points on the body to control symptoms suchas pain or nausea. Similar in concept to acupunc-ture, but without needles. See also acupuncture.

acupuncture The practice of inserting needlesinto specific points on the body with a therapeuticaim, such as to reduce pain or to induce anesthesiawithout the use of drugs. Traditional Chineseacupuncturists say the practice unblocks the flow ofa life force called ch’i; Western researchers believeacupuncture may affect production of endorphins,the body’s natural painkillers. In 1997, the NationalInstitutes of Health (NIH) issued a consensus state-ment stating that “There is sufficient evidence ofacupuncture’s value to expand its use into conven-tional medicine.” See also acupressure.

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acupuncturist A person skilled in the practice ofacupuncture, who may or may not be credentialedby an accrediting body.

acute Of short duration, rapid, and abbreviated inonset. A condition is termed acute in comparison toa subacute condition, which lasts longer or changesless rapidly; or a chronic condition, which may lastalmost indefinitely, with virtually no change. Eachdisease has a unique time scale: An acute myocar-dial infarction (heart attack) may last a week,whereas an acute sore throat may last only a day ortwo. See also chronic.

acute abdomen Medical shorthand for the acuteonset of abdominal pain. A potential medical emer-gency, an acute abdomen may reflect a major prob-lem with one of the organs in the abdomen, such asappendicitis (inflamed appendix), cholecystitis(inflamed gallbladder), a perforated ulcer in theintestine, or a ruptured spleen.

acute esophageal stricture See esophagealstricture, acute.

acute fatty liver of pregnancy AbbreviatedAFLP, liver failure in late pregnancy, usually ofunknown cause. Symptoms include nausea andvomiting, abdominal pain, yellowing of the skin andeyes (jaundice), frequent thirst (polydipsia),increased urination (polyuria), headache, andaltered mental state. Laboratory features of AFLPinclude low blood sugar (hypoglycemia), elevatedliver enzymes, and low levels of blood platelets.Untreated AFLP can cause complete liver failure,bleeding due to impaired blood clotting, and deathof the mother and fetus. AFLP is treated by deliver-ing the baby as soon as possible, often by inducingearly labor. It usually subsides after delivery anddoes not occur in subsequent pregnancies. In somecases AFLP is associated with an abnormality offatty-acid metabolism: a deficiency of the enzymelong-chain-3-hydroxyacyl-CoA dehydrogenease(LCHAD). The mother and father have half the nor-mal LCHAD activity, and the fetus has no LCHADactivity. This metabolic disease in the baby’s livercauses the fatty liver disease in the mother.

acute HIV infection See HIV infection, acute.

acute idiopathic polyneuritis See Guillain-Barre syndrome.

acute illness A disease with an abrupt onset and,usually, a short course.

acute leukemia Cancer of the blood cells thatcharacteristically comes on suddenly and, if not

treated, progresses quickly. In acute leukemia, theleukemic cells are not able to mature properly.

acute membranous gingivitis A progressiveand painful infection of the mouth and throat due tothe spread of infection from the gums. Symptomsinclude ulceration, swelling, and sloughing off ofdead tissue from the mouth and throat. Certaingerms (including fusiform bacteria and spiro-chetes) have been thought to be involved, but theactual cause is not yet known. Like most otherpoorly understood diseases, acute membranousgingivitis goes by many other names, includingacute necrotizing ulcerative gingivitis, fusospirillarygingivitis, fusospirillosis, fusospirochetal gingivitis,necrotizing gingivitis, phagedenic gingivitis, trenchmouth, ulcerative gingivitis, ulcerative stomatitis,Vincent angina, Vincent gingivitis, Vincent infection,and Vincent stomatitis.

acute mountain sickness The physical effect ofbeing in a high-altitude environment. AbbreviatedAMS, it is common at altitudes above 2,440meters (approximately 8,000 feet). Three-fourths ofpeople have mild symptoms of AMS at altitudes over3,048 meters (approximately 10,000 feet).Occurrence depends on the altitude, rate of ascent,and individual susceptibility. Symptoms begin 12 to24 hours after arrival at a new altitude and includeheadache, dizziness, fatigue, shortness of breath,loss of appetite, nausea, disturbed sleep, and gen-eral malaise. These symptoms tend to worsen atnight, when the respiratory drive is decreased.Symptoms should subside within 2 to 4 days,and can be treated by using pain medications suchas aspirin. Acetazolamide (brand name: Diamox)can also be used to minimize symptoms and may betaken as a preventive measure. Moderate AMS hasthe same symptoms as AMS, but the headaches can-not be relieved with medication, and both breathingand coordinated movements become difficult. Theonly remedies are advanced medications anddescent to lower altitudes. Severe AMS causes greatshortness of breath at rest, inability to walk,decreased mental status, and fluid buildup in thelungs. Severe AMS requires immediate descent tolower altitudes: 610 to 1,220 meters (approxi-mately 2,000 to 4,000 feet). See also acclimati-zation to altitude.

acute myelogenous leukemia See leukemia,acute myeloid.

acute myeloid leukemia See leukemia, acutemyeloid.

acute myocardial infarction A heart attack thatoccurs when the heart muscle is suddenly deprived

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of circulating blood. Abbreviated AMI. See alsoheart attack.

acute nonlymphocytic leukemia Seeleukemia, acute myeloid.

acute otitis media Painful inflammation of themiddle ear, typically with fluid in the middle ear,behind a bulging eardrum or a perforated eardrum,often with drainage of pus. The customary treatmentis antibiotics for 7 to 10 days. After antibiotic treat-ment, some children are left with fluid in the middleear, which can cause temporary hearing loss. Inmost children, the fluid eventually disappears spon-taneously. If a child has a bulging eardrum and isexperiencing severe pain, a myringotomy (surgicalincision of the eardrum) to release the pus may bedone. Tubes may be placed in the ear to drain fluid.See also ear infection.

acute peritonitis See peritonitis, acute.

acute respiratory distress syndromeRespiratory failure of sudden onset due to fluid inthe lungs (pulmonary edema), following an abruptincrease in the permeability of the normal barrierbetween the capillaries in the lungs and the air sacs.The muscles used in breathing are forced to workharder, causing labored and inefficient breathing.An abnormally low level of oxygen in the blood(hypoxemia) occurs. The types of acute lung injurythat may lead to ARDS include, but are not limitedto, aspiration of food or other items into the lungs,inhalation of a toxic substance, widespread infec-tion of the lungs, blood infection (sepsis), and near-drowning. Treatment frequently involves temporaryuse of a mechanical ventilator to help the patientbreathe.

acute thrombocytopenic purpura Suddenonset of low blood platelet levels, with bleeding intothe skin and elsewhere. Abbreviated ATP. ATP canhave many causes; for example, it can be a poten-tially serious complication during the acute phase ofmeasles infection.

acute-phase protein A protein whose plasmaconcentrations increase during certain inflamma-tory disorders. Perhaps the best-known acute-phaseprotein is C-reactive protein (CRP).

acyclovir A potent antiviral drug or medication(brand name: Zovirax) that works against severalhuman herpes viruses, Epstein-Barr virus, herpeszoster, varicella (chickenpox), cytomegalovirus,and other viruses. It is part of the AIDS drug AZT.See also AZT.

ad- Prefix indicating toward or in the direction of.For example, adduction is the movement of a limbtoward the midline of the body, and adrenal literallymeans “toward the kidney.”

ad lib Abbreviation of the Latin phrase ad libi-tum, meaning “as much as one desires” or “at yourdiscretion.” See also Appendix A, “PrescriptionAbbreviations.”

ADA 1 American Dental Association, a professionalorganization for dentists. Its Council on DentalEducation and Commission on Dental Accreditationare responsible for accrediting schools of dentistryand allied professions. 2 American DiabetesAssociation, a nonprofit health organization thatsponsors diabetes research, provides informationabout diabetes and diabetes prevention to patientsand others, and advocates for improved treatment ofpeople with diabetes. 3 Adenosine deaminase.

Adam’s apple The familiar feature on the front ofthe neck that is the forward protrusion of the thy-roid cartilage, the largest cartilage of the larynx. Ittends to enlarge at adolescence, particularly inmales. It is usually said to take its name from theextrabiblical story that a piece of the forbidden fruitstuck in Adam’s throat.

ADD 1 Attention deficit disorder. 2 Adenosinedeaminase deficiency.

addiction An uncontrollable craving, seeking,and use of a substance such as alcohol or anotherdrug. Dependence is such an issue with addictionthat stopping is very difficult and causes severephysical and mental reactions.

Addison’s anemia See anemia, pernicious.

Addison’s disease Chronic underfunction of theouter portion of the adrenal gland, most commonlydue to autoimmune destruction. Other causesinclude physical trauma to the adrenal gland, hem-orrhage, tuberculosis, and destruction of the pitu-itary gland cells that secrete adrenocorticotropichormone (ACTH), which normally controls theadrenal gland. Addison’s disease is characterized bybronzing of the skin, anemia, weakness, and lowblood pressure.

adducted thumbs Clasped thumbs, caused byabsence of the extensor pollicis longus and/or bre-vis muscles to the thumb. When associated withmental retardation, it is part of an X-linked syn-drome that affects mainly boys. See MASA syn-drome.

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adduction Movement of a limb toward the mid-line of the body. The opposite of adduction is abduc-tion.

adductor muscle See muscle, adductor.

adenine A nucleotide member of the base pairadenine-thymine (A-T) in DNA.

adenitis Inflammation of a gland.

adenocarcinoma A cancer that develops in thelining or inner surface of an organ and usually hasglandular (secretory) properties. More than 95 per-cent of prostate cancers are adenocarcinomas.

adenoid A mass of lymphoid tissue in the upperpart of the throat, behind the nose. When the ade-noids are enlarged due to frequent infections,breathing through the nose may become difficult.Surgical removal may be done, often accompaniedby removal of the tonsils. Also known as pharyngealtonsil.

adenoidectomy The surgical removal of the ade-noids.

adenoiditis Infection of the adenoids.

adenoma A benign tumor that arises in or resem-bles glandular tissue. If an adenoma becomes can-cerous, it is called an adenocarcinoma.

adenomyoma A nodule that forms aroundendometrial tissue in cases of adenomyosis. Seeadenomyosis.

adenomyosis A common, benign condition ofthe uterus in which the endometrium (the inneruterus) grows into the adjacent myometrium (theuterine musculature located just outside theendometrium). The myometrium may respond tothis intrusion with muscular overgrowth. If anisland of endometrial tissue is contained within themyometrium, it forms an adenomyoma. Also knownas endometriosis interna, endometriosis uterina,adenomyosis uteri, and adenomyometritis.

adenopathy Large or swollen lymph nodes.Lymph nodes can become enlarged as a result ofinflammatory diseases, infection, or cancer.Synonymous with lymphadenopathy.

adenosine deaminase An enzyme that plays akey role in salvaging purine molecules. AbbreviatedADA.

adenosine deaminase deficiency An autoso-mal recessive genetic condition that results insevere combined immunodeficiency disease. The

first successful gene therapy for this condition inhumans was done in 1990, by infusing patients withgenetically engineered blood cells.

adenosine triphosphate A nucleotide com-pound that is of critical importance for the storageof energy within cells and the synthesis of RNA.Abbreviated ATP.

adenovirus One of a group of viruses that cancause infections of the lung, stomach, intestine, andeyes. Symptoms resemble those of the commoncold. There are no effective medications for treatingadenovirus infection. Adenovirus infection typicallydoes not cause death or permanent problems. Morethan 40 types of adenoviruses have been recog-nized, all of which are extremely tiny. Adenovirusesare being used in research as a vehicle for genetherapy and as a vector for vaccines.

ADH Antidiuretic hormone.

ADH secretion, inappropriate A condition thatresults in the inability to produce dilute urine andimbalance of fluids and electrolytes in the body, par-ticularly lowering blood sodium. Symptoms includenausea, vomiting, muscle cramps, confusion, andconvulsions. This syndrome may occur with oat-celllung cancer, pancreatic cancer, prostate cancer, andHodgkin’s disease, among other disorders. Alsoknown as syndrome of inappropriate ADH secretionor SIADH.

ADHD Attention deficit hyperactivity disorder.

adhesion The union of two opposing tissue sur-faces. This term is often used to refer to the sides ofa wound, as well as to scar tissue strands that canform at the site of a previous operation, such aswithin the abdomen after a laparotomy.

adhesive capsulitis A condition in which a per-son has constant severe limitation of the range ofmotion of the shoulder due to scarring around theshoulder joint. Adhesive capsulitis is an unwantedconsequence of rotator cuff disease that involvesdamage to the rotator cuff. The affected joint ischaracteristically painful and tender to palpation.Physical therapy and cortisone injections are oftenhelpful. Surgery is used in advanced cases. Alsoknown as frozen shoulder.

adipose Fatty. Adipose refers to tissue made up ofmainly fat cells such as the yellow layer of fatbeneath the skin.

adiposis dolorosa See Dercum disease.

adjuvant A substance that helps and enhancesthe effect of a drug, treatment, or biologic system.

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adjuvant chemotherapy Chemotherapy givenafter removal of a cancerous tumor to further helpin treatment. Many chemotherapy drugs are mosteffective after the majority of the tumor has beenremoved.

ADLs Activities of daily living.

admitting physician The doctor responsible foradmitting a patient to a hospital or other inpatienthealth facility.

adnexa In gynecology, the appendages of theuterus, namely the ovaries, the Fallopian tubes, andthe ligaments that hold the uterus in place.

adrenal gland A small gland located on top ofthe kidney. The adrenal glands produce hormonesthat help control heart rate, blood pressure, the waythe body uses food, the levels of minerals such assodium and potassium in the blood, and other func-tions particularly involved in stress reactions.

adrenal medulla See medulla, adrenal.

adrenaline A stress hormone produced withinthe adrenal gland that quickens the heart beat,strengthens the force of the heart’s contraction, andopens up the bronchioles in the lungs, among othereffects. The secretion of adrenaline is part of thehuman “fight or flight” response to fear, panic, orperceived threat. Also known as epinephrine.

adult hemoglobin See hemoglobin A.

adult-onset diabetes Non-insulin-dependent,or type 2, diabetes, the most common form of dia-betes mellitus. Unlike patients with insulin-depend-ent, or type 1, diabetes, in whom the pancreas makesno insulin, patients with adult-onset diabetes producesome insulin, sometimes even large amounts.However, their bodies do not produce enough insulinor their body cells are resistant to the action ofinsulin. People with this form of diabetes are fre-quently overweight and can sometimes control theirdisease by losing weight through diet and exercise.Otherwise, they may need to combine insulin oranother diabetes medication with diet and exercise.See also diabetes, type 1.

adult-onset Still’s disease Still’s disease thatbegins in adulthood rather than in childhood. Seealso Still’s disease.

advance directive A document drawn up by apatient or, in some cases, the patient’s representa-tive to set treatment preferences and to designate asurrogate decision maker should the patientbecome unable to make medical decisions. Advance

directives include the living will, power of attorney,and health care proxy. See also DNR.

adverse event In pharmacology, any unexpectedor dangerous reaction to a drug or vaccine.

AED See automated external defibrillator.

aer-, aero- Prefix indicating air or gas, such asaerogastria (excess stomach gas).

aerobic Oxygen-requiring. Aerobic bacteria needoxygen to grow. Aerobic exercise requires the heartand lungs to work harder to meet the body’sincreased oxygen demand.

aerobic exercise Brisk exercise that promotesthe circulation of oxygen through the blood and isassociated with an increased rate of breathing.Examples include running, swimming, and bicy-cling.

aerophagia Literally, eating air, from the Greekwords aer, meaning “air,” and phagein, meaning“to eat.” Aerophagia is a common cause of stomachgas. Everyone swallows small amounts of air wheneating or drinking. However, activities such as rapideating or drinking, gum chewing, smoking, andwearing ill-fitting dentures may cause a significantincrease in swallowed air.

aerosinusitis Painful sinus troubles due tochanging atmospheric pressures. Aerosinusitis isthe cause of sinus pain when going up or down in aplane. Also known as barosinusitis and sinus baro-trauma.

aerosol A fine spray or mist. Medications inaerosol form can be administered via a nebulizerand inhaled.

aerotitis Middle ear problems due to changingatmospheric pressures, as when a plane descendsto land. Symptoms include ear pain, ringing ears,diminished hearing and, sometimes, dizziness. Alsoknown as aerotitis media, barotitis, barotitis media,and otic barotrauma.

Aesculapius The ancient Roman god of medi-cine, whose staff with a snake curled around it iscommonly used as a symbol of medicine. Accordingto mythology, Aesculapius’s children includedHygeia, the goddess of health, and Panaceia, thegoddess of healing.

affective disorder A psychiatric disorder thataffects the control of mood. See bipolar disorder;cyclothymia; depression; seasonal affective dis-order.

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afferent Carrying toward. A vein is an afferentvessel because it carries blood from the bodytoward the heart. The opposite of afferent is effer-ent.

afferent nerve A nerve that carries impulsestoward the central nervous system.

afferent vessel A vessel that carries bloodtoward the heart. A vein or venule.

AFLP Acute fatty liver of pregnancy.

AFO Ankle-foot orthosis.

AFP Alpha-fetoprotein.

African tapeworm See Taenia saginata.

African tick typhus See typhus, African tick.

afterbirth The placenta and the fetal membranesthat are normally expelled from the uterus after thebirth of a baby. See also placenta.

aftercare Medical care and instructions forpatients after leaving a medical facility.

agammaglobulinemia Total or near-totalabsence of infection-fighting antibodies belongingto the class called gamma globulins.Agammaglobulinemia can be due to certain geneticdiseases or caused by acquired diseases, includingAIDS.

agenesis Lack of development. For example, age-nesis of a toe means the toe failed to form.

agenesis, sacral See caudal regression syn-drome.

agenesis of the gallbladder A condition inwhich the gallbladder fails to develop. It occurs in 1in about every 1,000 people, usually without addi-tional birth defects.

agent, antihypertensive See antihypertensive.

agent, anti-infective See anti-infective.

Agent Orange An herbicide and defoliant con-taining 2,4-D and 2,4,5-T, as well as traceamounts of dioxin. Agent Orange was used as adefoliant in the Vietnam War. There has been con-cern about Agent Orange potentially causing cancerand birth defects.

age-related macular degeneration See mac-ular degeneration.

ageusia An inability to taste sweet, sour, bitter, orsalty substances. People who can taste sweet, sour,bitter, or salty substances but have a reduced abilityto do so are said to have hypogeusia.

aggressive 1 In cancer medicine, quickly grow-ing or tending to spread rapidly. For example, anaggressive tumor. 2 In psychiatry, having a ten-dency to aggression or belligerent behavior.

aggressive fibromatosis See desmoid tumor.

agnosia An inability to recognize sensory inputssuch as light, sound, and touch). Agnosia is typicallya result of brain injury. For example, damaging theback part of the brain can cause visual agnosia(inability to properly recognize objects by sight).

agonist A substance that acts like another sub-stance and therefore stimulates an action. Agonist isthe opposite of antagonist. Antagonists and agonistsare key players in the chemistry of the human bodyand in pharmacology.

agoraphobia An abnormal and persistent fear ofpublic places or open areas, especially those fromwhich escape could be difficult or in which helpmight not be immediately accessible. Persons withagoraphobia frequently also have panic disorder.People with mild agoraphobia often live normallives by avoiding anxiety-provoking situations. In themost severe agoraphobia, the victims may be inca-pacitated and homebound. Agoraphobia tends tostart in the mid to late 20s, and the onset mayappear to be triggered by a traumatic event.

agranulocytosis A marked decrease in the num-ber of granulocytes (neutrophils). Agranulocytosisresults in frequent chronic bacterial infections ofthe skin, lungs, throat, and other areas. It can be aninherited genetic condition or acquired as, forexample, in leukemia. See also agranulocytosis,infantile genetic; granulocytopenia; severe con-genital neutropenia.

agranulocytosis, infantile genetic An inheritedcondition characterized by a lack of granulocytes(neutrophils), a type of white blood cell that is impor-tant in fighting infection, and a predisposition to fre-quent bacterial infections. Also known as Kostmanndisease or syndrome and genetic infantile agranulocy-tosis. See also agranulocytosis; granulocytopenia;severe congenital neutropenia.

agreement, arbitration See arbitration agree-ment.

Aicardis syndrome A rare genetic disorder thatoccurs only in females and is caused by congenital

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absence of the corpus callosum, a large bundle ofnerves that connects the left and right sides of thebrain. Features include epilepsy that emerges ininfancy and is difficult to control, vision problems dueto maldeveloped retinas, developmental delay, andsometimes physical deformities of the spine, face,and/or heart. See also epilepsy; seizure disorders.

AID Artificial insemination by donor.

AIDS Acquired immunodeficiency syndrome, asyndrome caused by infection with the humanimmunodeficiency virus (HIV), with ensuing com-promise of the body’s immune system. Featuresinclude deficiency of certain types of leukocytes,especially T cells; infection with opportunistic infec-tions that take advantage of the impaired immuneresponse, such as tuberculosis, bacterial pneumo-nia, human herpes virus, or toxoplasmosis; certaintypes of cancer, particularly Kaposi sarcoma; inabil-ity to maintain body weight (wasting); and inadvanced cases, AIDS dementia complex. Treatmentfor AIDS has advanced rapidly. Antiviral, antibacter-ial, and immune-boosting medications, among othertreatments, are part of current treatment protocols.

AIDS dementia complex A brain disorder inpeople with severe AIDS, causing loss of thinkingcapacity and affecting the ability to function. AIDSdementia complex is considered an AIDS-definingillness—that is, one of the serious illnesses thatoccurs in HIV-positive individuals warranting anAIDS diagnosis, according to the definition of AIDSby the Centers for Disease Control and Prevention(CDC).

AIDS-related complex A term used in the earlyyears of the AIDS epidemic to describe people withHIV infection who had only mild symptoms of illness,such as swollen lymph glands. It is rarely used today.Abbreviated ARC.

airway The path that air follows to get into andout of the lungs. The mouth and nose are the nor-mal entry and exit ports for the airway. Entering airthen passes through the back of the throat (phar-ynx) and continues through the voice box (larynx),down the trachea, to finally pass through thebronchi.

airway obstruction Partial or complete block-age of the breathing passages to the lungs. Causesinclude the presence of foreign matter, allergicreactions, infections, anatomical abnormalities, andtrauma. Associated respiratory distress may be sud-den, with only a cough for a warning. There is oftenagitation in the early stages. Other signs includelabored, ineffective breathing, until the person is no

longer breathing (apneic). Loss of consciousnessoccurs if the obstruction is not relieved. Treatmentof airway obstruction due to a foreign body includesthe Heimlich maneuver for adults, a series of fiveabdominal thrusts for children over 1 year of age,and a combination of five back blows with the flat ofthe hand and five abdominal thrusts with two fingerson the upper abdomen for infants.

AKA Above-the-knee amputation, generally per-formed when the leg is not medically viable or toprevent the spread of disease to the tissues abovethe knee from below.

akathisia A movement disorder characterized bya feeling of inner restlessness and a compellingneed to be in constant motion, as well as by actionssuch as rocking while standing or sitting, lifting thefeet as if marching on the spot, and crossing anduncrossing the legs while sitting. People withakathisia are unable to sit or keep still, complain ofrestlessness, fidget, rock from foot to foot, andpace.

akinesia The state of being without movement.

akinetic Related to the loss of the normal abilityto move the muscles.

akinetic epilepsy See epilepsy, akinetic.

akinetic mutism See mutism, akinetic.

alanine aminotransferase An enzyme normallypresent in liver, skeletal muscle, and heart cells.Abbreviated ALT. ALT is released into blood when theliver, skeletal muscle, or heart is inflamed orinjured by diseases, conditions, or medications.Also known as serum glutamic pyruvic transami-nase (SGPT).

albinism A pigmentation disorder characterizedby partial or total lack of the pigment melanin in theskin, hair, and iris. Albinism is caused by an auto-somal recessive gene and can occur in people ofany ethnic background. People with albinism havedelicate skin that sunburns and develops skin can-cer easily, and they may suffer from eye disorders.See also Hermansky-Pudlak syndrome; vitiligo.

albino A person with albinism. The term was firstapplied by the Portuguese to people in West Africa,who may have had partial or complete albinism.

albuginea Tough white fibrous tissue. The tunicaalbuginea of the testis, for example, is the layer ofdense whitish inelastic tissue that surrounds thetestis.

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albumin The main protein in human blood andthe key to regulating the osmotic pressure of blood.Chemically, albumin is soluble in water, precipitatedby acid, and coagulated by heat.

albuminuria More than the normal amount ofalbumin in the urine. Albuminuria can be a sign thatprotein is leaking through the kidney, most oftenthrough the glomeruli, or a sign of significant kid-ney disease. It may also be the harmless result ofvigorous exercise. Also known as proteinuria.

alcohol An organic substance formed when ahydroxyl group is substituted for a hydrogen atom ina hydrocarbon. The type of alcohol used in alco-holic beverages, ethanol, derives from fermentingsugar with yeast. After alcohol is ingested, the bodyconverts it to sugar-based fuel. Alcohol acts as acentral nervous system depressant, and it may bepart of solutions used as preservatives, antiseptics,or medications.

alcohol abuse Use of alcoholic beverages toexcess, either on individual occasions (binge drink-ing) or as a regular practice. For some individu-als—children or pregnant women, forexample—almost any amount of alcohol use maybe legally considered “alcohol abuse.” Heavy alco-hol abuse can cause physical damage and death.

alcohol poisoning A condition in which a toxicamount of alcohol has been consumed, usually in ashort period of time. The affected individual maybecome extremely disoriented, unresponsive, orunconscious, with shallow breathing. Because alco-hol poisoning can be deadly, emergency treatment isnecessary.

alcohol use in pregnancy The consumption ofalcohol during pregnancy, which can damage thefetus. See also fetal alcohol effect; fetal alcoholsyndrome.

Alcoholics Anonymous A free self-help organi-zation founded to assist people addicted to alcoholin breaking old behavior patterns and gaining sup-port for consistently living a sober lifestyle.

alcoholism Physical dependence on alcohol tothe extent that stopping alcohol use would bring onwithdrawal symptoms. In popular and therapeuticparlance, the term may also be used to refer toingrained drinking habits that cause health or socialproblems. Treatment requires first ending the phys-ical dependence and then making lifestyle changesthat help the individual avoid relapse. In somecases, medication and hospitalization are necessary.Alcohol dependence can have many serious effects

on the brain, liver, and other organs of the body,some of which can lead to death.

aldosterone A hormone produced by the outerportion (cortex) of the adrenal gland. Aldosteroneregulates the balance of water and electrolytes in thebody, encouraging the kidney to excrete potassiuminto the urine and retain sodium, thereby retainingwater. It is classified as a mineralocorticoid hor-mone.

aldosteronism See Conn syndrome.

alexia Loss of the ability to read or understandthe written word, due either to brain damage thatdisconnects these functions or to temporary dys-function caused by abnormal electrical or chemicalactivity in the brain.

alienist French term for a psychologist, a psychi-atrist, or another practitioner who cares for thementally ill.

alimentary Concerning food, nourishment, andthe organs of digestion. From the Latin alimentum,meaning nourishment.

alkaline phosphatase An enzyme that liberatesphosphate under alkaline conditions and is made inliver, bone, and other tissues. Alkaline phosphatasecan be measured in a routine blood test.Abnormally high serum levels of alkaline phos-phatase may indicate bone disease, liver disease, orbile duct obstruction.

alkalosis Relatively too much base in the bloodand body, an abnormal condition resulting from theaccumulation of base or the depletion of acid. ThepH of an alkalotic body measures above normal.The opposite of alkalosis is acidosis.

alkaptonuria A genetic metabolic disorder dueto deficiency of the enzyme homogentisic acid(HGA) dioxygenase. Deficiency of this enzyme leadsto the three cardinal features of alkaptonuria (thepresence of homogentisic acid in the urine),ochronosis (bluish-black pigmentation in connec-tive tissue), and arthritis. Urine that turns dark is acharacteristic feature.

allele An alternative form of a gene.

allergen A substance that can cause an allergicreaction. Common allergens include ragweedpollen, animal dander, and mold.

allergic conjunctivitis Inflammation of thewhites of the eyes (conjunctivae), with itching, red-ness, and tearing, due to allergy.

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allergic granulomatosis See Churg-Strauss syndrome.

allergic reaction A hypersensitive immuneresponse to a substance. An allergic reaction canoccur when the immune system attacks a normallyharmless substance. The allergic immune systemcalls upon a protective antibody calledimmunoglobulin E (IgE) to fight these invading sub-stances. In the melee, cells called mast cells releasea variety of strong chemicals, including histamine,into the tissues and blood. This chemical release isirritating and causes itching and swelling and canalso lead to lung airway narrowing and throat tight-ening, as is found in asthma, as well as to loss ofvoice. For example, this is how hay fever and aller-gic pink eye (conjunctivitis) occur. See also allergicconjunctivitis; allergic rhinitis; anaphylacticshock; asthma.

allergic rhinitis Medical term for hay fever, anallergic reaction that mimics a chronic cold.Symptoms include nasal congestion, a clear runnynose, sneezing, nose and eye itching, and tearing ofthe eyes. Postnasal dripping of clear mucus frequentlycauses a cough, loss of smell is common, and occa-sionally loss of taste. Nosebleeds may occur. Alsoknown as June cold and summer cold.

allergic rhinitis, perennial Allergic rhinitisthat occurs throughout the year.

allergic rhinitis, seasonal Allergic rhinitis thatoccurs during a specific season.

allergic salute The characteristic gesture of aperson with allergic rhinitis: rubbing his or hernose with the index finger.

allergic vasculitis See Churg-Strauss syn-drome.

allergy Hypersensitivity of the body’s immunesystem in response to exposure to specific sub-stances (antigens), such as pollen, bee stings, poi-son ivy, drugs, or foods. See also allergic reaction;anaphylactic shock.

allergy desensitization Stimulation of theimmune system with gradually increasing doses ofthe substances to which a person is allergic in orderto modify or stop the allergic response. This form oftreatment is very effective for allergies to pollen,mites, animal dander, and stinging insects, includ-ing bees, hornets, yellow jackets, wasps, velvet ants,fire ants, and certain necessary medications.

allergy scratch test See allergy skin test.

allergy skin test A test in which a small drop ofthe suspected allergy-provoking substance (aller-gen) is placed on the skin and the skin is then gen-tly scratched through the drop with a sterile needle.If the skin reddens and, more importantly, if itswells, the test is read as positive, and allergy to thatsubstance is considered probable.

allergy to cockroaches An allergic reaction totiny protein particles shed or excreted by cock-roaches. Asthma can be due to exposure to cock-roach allergens. Removing cockroach allergensfrom the home is not an easy job, but it can go farin reducing the frequency and severity of asthmaand other allergic reactions.

allograft The transplant of an organ or tissuefrom one individual to another of the same specieswith a different genotype. For example, a transplantfrom one person to another, but not an identicaltwin, is an allograft. Allografts account for manyhuman transplants, including those from cadaveric,living related, and living unrelated donors. Alsoknown as an allogeneic graft or a homograft.

allopath A term sometimes applied to a physi-cian who practices allopathy, or conventional medi-cine. See also allopathy.

allopathic medicine See allopathy.

allopathy The system of medical practice thattreats disease by the use of remedies to produceeffects different from those produced by the diseaseunder treatment. Doctors of medicine (MDs) prac-tice allopathic medicine. The term “allopathy” wascoined to designate conventional medicine asopposed to homeopathy, the system of therapybased on the concept that disease can be treatedwith drugs (in minute doses) thought capable ofproducing the same symptoms in healthy people asthe disease itself. Allopathy is also known as con-ventional medicine. See also allopath.

alopecia Baldness. Temporary alopecia mayoccur as a result of chemotherapy. Permanentalopecia may result from any of several conditions,including common male-pattern baldness.Radiation therapy administered to the head can alsocause permanent alopecia due to irreversible dam-age to the hair follicles. See also alopecia areata;alopecia capitis totalis; alopecia universalis;alopecia, traumatic.

alopecia, traumatic Hair loss caused by injuryto the scalp. Common causes include the use ofcaustic hair straighteners, especially those thatinclude lye as an ingredient; stress traction injury

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from tight rollers and braiding; overheating of thehair shafts; and compulsive pulling out of hair (tri-chotillomania).

alopecia areata Patchy baldness that typicallybegins with rapid hair loss on discrete areas of thescalp and sometimes progres