Neurophysiology Cases

7/27/2019 Neurophysiology Cases

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Qestion . 3. A 15-yr-old boy has lost his ability to walk. On physical examination,his ankle and knee deep tendon reflexes are noted to be diminished. The weaknessis greatest in peripheral muscles. Cranial nerves all are normal. One week before

these symptoms arose, he returned from a camping trip. The most likely diagnosisis:

Myasthenia gravis

Organophosphate poisoning

Spinal muscular atrophy

Botulism

Tick paralysisExplanation: Ticks (wood or dog) may produce a motor-sensory neuropathy indistinguishable from Guillain-Barrsyndrome. On removal of the tick (often on the scalp), theparalysis rapidly resolves. (See Chapter 605 in NelsonTextbook of Pediatrics, 17th ed.)

Question . 4. A 10-yr-old girl has had diplopia and ptosis and weakness of her neckflexors for 2 mo. Symptoms are worse in the evening and are usually less severeon awakening in the morning. She has no fasciculations or myalgias, and her deeptendon reflexes are 1-2+. The most likely diagnosis is:

Hysterical weakness

Muscular dystrophy

Spinal muscular atrophy

Botulism

Myasthenia gravisExplanation: Myasthenia gravis is characterized by

progressive muscle weakness that is exacerbated by repetitivemuscle use. Classically, the facial and extraocular muscles areinvolved. (See Chapter 603 in Nelson Textbook of Pediatrics,17th ed.)


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Question . 5. A 4-yr-old has difficulty in climbing stairs, slow motor development,and hypertrophied calf muscles. The most likely diagnosis is:

Myasthenia gravis

Myotonia congenita

Duchenne muscular dystrophyExplanation: Duchenne muscular dystrophy is also calledpseudohypertrophic muscular dystrophy. (See Chapter 600 inNelson Textbook of Pediatrics, 17th ed.)

Hypokalemic periodic paralysis

Central core disease

Question . 6. All of the following statements regarding creatine kinase (CK) are trueexcept:

It is the most useful serum enzyme reflecting damaged musclefibers

The MM isozyme is found primarily in skeletal muscle

The MB isozyme is found primarily in cardiac muscle

The BB isozyme is found primarily in smooth muscleExplanation: Creatine kinase (CK) is one of several lysosomalenzymes released by damaged or degenerating muscle fibersand is the most useful in laboratory measurement of theseenzymes in serum. CK is found in only three organs and maybe separated into corresponding isozymes: MM for skeletalmuscle, MB for cardiac muscle, and BB for brain. (See Chapter598 in Nelson Textbook of Pediatrics, 17th ed.)


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Question . 7. All of the following statements regarding congenital neuromusculardisorders are true except:

Most are hereditary

Most are nonprogressive conditions

The definitive diagnosis is best made by electromyography(EMG)Explanation: The definitive diagnosis of congenitalneuromuscular disorders is best determined by histopathologicfindings in the muscle biopsy sample. Most of the congenitalmyopathies are hereditary; some are sporadic. In a fewconditions for which the defective gene has been identified, the

diagnosis may be established using the specific molecularprobe on lymphocytes. (See Chapter 599 in Nelson Textbookof Pediatrics, 17th ed.)

Diagnosis for some disorders may be confirmed by geneticanalyses of lymphocytes

Hypotonia is a common feature

Question . 8. Characteristic features of muscular dystrophies include which of thefollowing?

They are a primary myopathy

They have a genetic basis

The course is progressive

Degeneration and death of muscle fibers occur at some stageof disease

All of the above

Explanation: The muscular dystrophies are a group ofunrelated disorders, each transmitted by a different gene andeach differing in its clinical course and expression. Themuscular dystrophies are distinguished from other neurogenicdisorders by the four obligatory criteria listed in the question.(See Chapter 600 in Nelson Textbook of Pediatrics, 17th ed.)


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Question . 9. All of the following statements regarding Duchenne musculardystrophy are true except:

It is the most common hereditary neuromuscular disease

It is inherited as an autosomal dominant traitExplanation: Duchenne muscular dystrophy, the mostcommon hereditary neuromuscular disorder, is inherited as anX-linked recessive trait. The gene is on the X chromosome atthe Xp21 locus. (See Chapter 600 in Nelson Textbook ofPediatrics, 17th ed.)

Symptoms are rarely present at birth or in early infancy

The serum creatine kinase is consistently greatly elevated

It is more common in males

Question . 10. Characteristic clinical manifestations of Duchenne musculardystrophy include:

Cardiomyopathy

Intellectual impairment

Weakness of respiratory muscles

Scoliosis

All of the aboveExplanation: Cardiomyopathy is a constant feature ofDuchenne muscular dystrophy, although the severity of cardiacinvolvement does not necessarily correlate with the degree ofskeletal muscle weakness. Intellectual impairment occurs in allpatients, although only 20-30% have an intelligence quotient(IQ) of less than 70. Scoliosis is common. (See Chapter 600.1

in Nelson Textbook of Pediatrics, 17th ed.)


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Question . 11. All of the following are associated with constant muscle weaknessexcept:

Hypothyroidism

Hyperparathyroidism

Corticosteroids

Hyperaldosteronism (Conn syndrome)Explanation: Thyrotoxicosis causes proximal muscleweakness and wasting accompanied by electromyogram(EMG) changes. Hypothyroidism, whether congenital oracquired, consistently produces proximal muscle weakness

and hypotonia. Hyperparathyroidism causes weakness andreversible muscle wasting. Both natural Cushing disease andexogenous corticosteroid administration may cause proximalmuscle weakness. Hyperaldosteronism is accompanied byepisodic and reversible muscle weakness. (See Chapter 598 inNelson Textbook of Pediatrics,17th ed.)

Question . 12. All of the following statements regarding malignant hyperthermia aretrue except:

It is inherited as an autosomal dominant trait

Acute episodes are typically precipitated by intravenousadministration of dyes for radiographic studiesExplanation: Acute episodes of malignant hyperthermia areprecipitated by exposure to general anesthetics andoccasionally to local anesthetic drugs. Acute attacks may beprevented by administration of dantrolene sodium before ananesthetic is administered. (See Chapter 602.2 in NelsonTextbook of Pediatrics, 17th ed.)

Myoglobinuria may result in tubular necrosis and acute renalfailure

Attacks may be prevented by administration of dantrolenesodium

Metabolic acidosis may be severe


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Question . 13. Which of the following is the etiology in most cases of myastheniagravis?

Inheritance as a recessive trait

Inheritance as an X-linked trait

Postinfectious, usually after either influenza or chickenpox

Autoimmune disorderExplanation: Myasthenia gravis is an autoimmune disorder. Arare familial form is probably an autosomal recessive trait but isnot associated with plasma anti-anti-acetylcholine antibodies.(See Chapter 603 in Nelson Textbook of Pediatrics, 17th ed.)

Idiopathic

Question . 14. Which of the following is the earliest and most consistent sign ofmyasthenia gravis?

Gowers sign

Trendelenburg gait

Ptosis and extraocular muscle weakness

Explanation: Ptosis and some degree of extraocular muscleweakness are the earliest and most constant signs inmyasthenia gravis. Older children may complain of diplopia.(See Chapter 603.1 in Nelson Textbook of Pediatrics, 17th ed.)

Respiratory muscle weakness

Head lag


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Question . 15. The best method for diagnosis of myasthenia gravis is:

Assay for anti-acetylcholine antibodies

Nerve conduction velocity (NCV) studies

Electromyogram (EMG)Explanation: Myasthenia gravis is one of the fewneuromuscular diseases in which an electromyogram (EMG) ismore diagnostic than muscle biopsy. A decremental responseoccurs in response to repetitive nerve stimulation; the musclepotentials diminish rapidly in amplitude until the musclebecomes refractory to further stimulation. Motor nerveconduction velocity remains normal. Plasma anti-acetylcholine

antibodies should be assayed but are inconsistently found,being present in only one third of adolescents. (See Chapter603.1 in Nelson Textbook of Pediatrics, 17th ed.)

Nerve biopsy

Muscle biopsy

Question . 16. Which of the following is a common clinical manifestation ofmyasthenia gravis?

Cardiomyopathy

Intellectual impairment

Weakness of respiratory musclesExplanation: If untreated, myasthenia gravis is usuallyprogressive and may become life-threatening because ofrespiratory muscle weakness. Cardiomyopathy is not a featureof myasthenia gravis, and electrocardiogram (ECG) findingsremain normal. (See Chapter 603.1 in Nelson Textbook ofPediatrics, 17th ed.)

Scoliosis

Headache


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Question . 17. A 1-day-old newborn, born to a myasthenic mother, has generalizedhypotonia and weakness. Which of the following best describes the prognosis?

Greatly increased risk of the complete picture of myastheniagravis

Small but increased risk of the complete picture of myastheniagravis

No increased risk of myasthenia gravisExplanation: After the abnormal (maternally derived)antibodies disappear, offspring born to myasthenic mothershave normal muscle strength and are not at increased risk formyasthenia gravis in later life. (See Chapter 603.1 in Nelson

Textbook of Pediatrics, 17th ed.)

Some residual weakness until puberty but no increased risk ofmyasthenia gravis

Episodes of diminishing severity of muscle weakness untilpuberty

Question . 18. A 4-yr-old child with a history of poor sucking and swallowing as aninfant recently experienced excessive sweating and blotchy erythema, especiallywhen excited. Walking is clumsy. There has been new onset of episodes of cyclic

vomiting lasting 24-27 hr, with retching and vomiting every 15-20 min as well asprofuse sweating, blotchy erythema, and evidence of apprehension and irritability.The most likely diagnosis is:

Duchenne muscular dystrophy

Fabry disease

Chronic organophosphate intoxication

Familial dysautonomia (Riley-Day syndrome)E

xplanation: Familial dysautonomia (Riley-Day syndrome) isusually expressed in infancy as poor sucking and feeding.Autonomic crises usually begin after age 3 yr. (See Chapter606.1 in Nelson Textbook of Pediatrics, 17th ed.)

Guillain-Barr syndrome


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Question . 19. A 4-yr-old child presents with symmetric weakness that began in thelower extremities and subsequently progressed over 10-14 days to involve the trunkand upper limbs. Deep tendon reflexes are absent. There are no sensory deficits or

bowel or bladder dysfunction. Nerve conduction velocity test results are abnormal.The cerebrospinal fluid shows protein of 78 mg/dL and 5 white blood cells. Themost likely diagnosis is:


Fabry disease

Familial dysautonomia (Riley-Day syndrome)

Bell palsy

Explanation: Guillain-Barr syndrome is a postinfectiouspolyneuropathy that causes demyelination, primarily in themotor nerves. The onset is typically gradual, with symmetricinvolvement that begins in the lower extremities andprogressively involves the trunk and upper limbs. Bulbarinvolvement occurs in about half of cases. Spontaneousrecovery usually occurs in 2-3 weeks. (See Chapter 607 inNelson Textbook of Pediatrics, 17th ed.)


Question . 20. A 9-yr-old boy presents with paresis of the upper and lower portionsof the face and loss of taste on the right side of the anterior portion of the tongue.On physical examination, the corner of the mouth droops, and he is unable to closethe right eye tightly. Findings on the remainder of the physical examination arenormal. The most likely diagnosis is:


Fabry disease

Familial dysautonomia (Riley-Day syndrome)

Bell palsyExplanation: Bell palsy is an acute unilateral facial nerve palsythat is not associated with other cranial neuropathies ofbrainstem dysfunction. It is a common disorder at all ages andtypically develops about 2 weeks after a systemic infection,especially herpes simplex virus and Lyme disease. (SeeChapter 608 in Nelson Textbook of Pediatrics, 17th ed.)



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Question . 21. A 5-yr-old boy has been falling frequently and cannot climb stairs aswell as he did 6-12 months ago. He is an only child, and there is no family history ofneurologic disease. On examination, he has proximal weakness of the legs and

enlargement of the calves, but no weakness of cranial or extraocular muscles.Serum creatine kinase is 16,400 IU/L. You suspect Duchenne muscular dystrophyand request assay for a molecular marker in blood for dystrophinopathy, but theresult is normal. The next diagnostic test likely to confirm or refute your clinicaldiagnosis is:

EMG

Detailed physical therapy evaluation

A repeat of the blood marker assay in the child and also in the

mother

Muscle biopsy

MRI study of calves and thighsExplanation: (See Chapters 598 and 599 in Nelson Textbookof Pediatrics, 17th ed.)

Question . 22. A male neonate has respiratory distress, dysphagia, andgeneralized muscular hypotonia and weakness. Pregnancy was uncomplicated, butthe mother reports weak fetal movements in the last trimester. Delivery at term was

uneventful, and Apgar scores at 1 and 5 min were 7 and 8. On examination, he hasa dolichocephalic head, high-arched palate, thin muscle mass in trunk andextremities, and undescended testes. This clinical picture is least suggestive of:

Nemaline rod myopathy

X-linked myotubular myopathy

Duchenne muscular dystrophyExplanation: (See Chapter 599 in Nelson Textbook ofPediatrics, 17th ed.)

Myotonic dystrophy, neonatal form

Congenital muscular dystrophy with merosin deficiency


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Question . 23. An 8-yr-old girl demonstrates progressive ataxia, deterioration inspeech and academic performance in school, tingling paresthesias of the feet, andweakness of the ankles with inability to dorsiflex her feet. Nerve conduction velocity

studies show moderate slowing in motor component of the peroneal nerves, and anMRI study of the brain reveals white matter lesions in the periventricular whitematter and cerebellum. These findings would be compatible with any of thefollowing except:

Metachromatic leukodystrophy

Hereditary motor-sensory neuropathy type I (Charcot-Marie-Tooth disease)Explanation: (See Chapter 604 in Nelson Textbook ofPediatrics, 17th ed.)

Giant axonal neuropathy

Globoid cell leukodystrophy (Krabbe disease)

Adrenoleukodystrophy

Question . 24. The most frequent toxic neuropathy in children in the United Statescurrently is due to:

Lead

Arsenic

Organophosphates used in insecticides

Various industrial and agricultural pollutants in drinking water

Drugs used in chemotherapyExplanation: (See Chapter 605 in Nelson Textbook ofPediatrics, 17th ed.)


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Question . 25. A 15-yr-old boy complains of slowly progressive difficulty withcoordination and intermittent diplopia. He also has mild generalized weakness.Studies demonstrate normal serum creatine kinase, a mild lactic acidosis, and ECG

evidence of cardiomyopathy. EMG shows nonspecific myopathic features. Yourprovisional diagnosis, to be confirmed by other tests, is:

Mitochondrial cytopathyExplanation: (See Chapter 602 in Nelson Textbook ofPediatrics, 17th ed.)

Facioscapulohumeral muscular dystrophy

Congenital muscle fiber-type disproportion

Metachromatic leukodystrophy

Multiple sclerosis

Question . 26. The muscle biopsy in mitochondrial cytopathies may show all of thefollowing histopathologic features except:

Ragged-red fibers with trichrome stain

Lymphocytic infliltrates in perivascular and interstitialspaces

Explanation: (See Chapter 602 in Nelson Textbook ofPediatrics, 17th ed.)

Loss of cytochrome c oxidase (COX) activity in some but not allmyofibers

Ultrastructural abnormalities in mitochondrial cristae

Increased lipid within myofibers


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Question . 27. An 8-yr-old girl develops progressive proximal weakness, easyfatigue, a waddling gait, and myalgias of the thighs and shoulders over a period of 6weeks, and a violaceous rash appears over the malar areas of her face and the

extensor surfaces of the finger joints. Tendor reflexes are preserved. No heartmurmur is heard, and she has no visceromegaly, generalized lymphadenopathy, orfever. The most likely diagnosis is:

Systemic lupus erythematosus (SLE)

Polymyositis

Facioscapulohumeral muscular dystrophy

Viral myositis with exanthema

DermatomyositisExplanation: (See Chapter 149 in Nelson Textbook ofPediatrics, 17th ed.)

Question . 28. A 13-yr-old girl develops ptosis, diplopia, and difficulty swallowingbut is afebrile and otherwise in good health. On examination, her ptosis is noted toincrease with sustained upward gaze for 30 sec. No weakness of the extremities orlimb girdles is detected, and she has no myalgias or tenderness of muscles topalpation. The initial diagnostic test most likely to confirm the diagnosis is:

Anti-acetylcholine receptor antibodies in blood

Computed tomography of the thorax for thymoma

Motor nerve conduction velocity studies and EMG

Edrophonium (Tensilon) testExplanation: (See Chapter 603 in Nelson Textbook ofPediatrics, 17th ed.)

Muscle biopsy

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