HEALTH & WELFARE VET t Equine Brain Disorders · neonatal intensive care and medical imaging. She...
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Presented by ROSSDALES EQUINE HOSPITAL Cotton End Road, Exning, Newmarket CB8 7NN, Tel: 01638 577754 E: [email protected] www.rossdales.com Celia M Marr BVMS, MVM, PhD, DEIM, DipECEIM, MRCVS Celia is a European and RCVS Specialist in Equine Internal Medicine and works with both inpatients and outpatients with medical problems at Rossdales Equine Hospital, where she is responsible for internal medicine and cardiology. Her clinical and research interests are in cardiovascular medicine, internal medicine, adult and neonatal intensive care and medical imaging. She has published over 50 research papers and educational material relating to a range of medical disorders of the horse, concentrating on cardiovascular disease and diagnostic methods in medical disorders including editing a book on Cardiology of the Horse, the second edition of which was published in 2010. Celia is an Honorary Professor of the University of Glasgow, Editor-in-Chief of Equine Veterinary Journal, and Chairman of the Veterinary Advisory Committee of the Horserace Betting Levy Board. HEALTH & WELFARE rain diseases are very uncommon in horses. Figures on the exact prevalence are not available but review of recent cases seen by the medical team at Rossdales Equine Hospital suggest that just over 0.5% of horses admitted for complex medical problems have disorders of the brain. There are a number of important infectious diseases worldwide that can affect the equine brain but we are fortunate that currently in the UK these diseases are not endemic. The two most common causes of equine brain disease in the UK are head trauma and a group of diseases that together are classified as metabolic encephalopathy. Occasionally horses suffer from epilepsy, although not as often as dogs. Meningitis is mainly a disease of the young and very rarely, we see young horses which congenital or developmental problems. Anatomy and functions of the brain In simple terms, the brain can be divided into several regions: • The forebrain or cerebral cortex is where consciousness resides and this area is responsible for perception, information processing and voluntary control of movement. Damage to this area leads to change in behaviour, loss or reduction in consciousness and can lead to central blindness – where the signals are coming in from the eyes but the brain is not capable of processing that information. • The cerebellum sits behind the cerebral cortex and provides fine control and co-ordination of movement. • The brainstem serves as a bridge with interconnecting neural tracts coming down from the cortex and cerebellum and leaving towards the spinal column. This is also where specialised areas called cranial nerve ganglia are located. These are groups of cell bodies from the cranial nerves form interconnections critical to their control. These cranial nerves include the trigeminal and facial nerves which co-ordinate sensation and movement of the face, and the vestibular ganglia that controls the position of the head, eyes and trunk relative to gravity. Damage in this area can cause loss of muscles of the cheek which compromises swallowing, loss of muscle tone around the lips, ear and eyelid, and if the vestibular system is damaged, the horse will develop a head tilt and loose its balance. Vestibulospinal tracts integrate with the spinal column and disruption of these critical connections affects the horse’s gait. Brain Trauma Horses are prone to trauma and when this involves the head, the consequences can be particularly devastating. Clinical signs can range from mild disorientation through to seizures, profound depression or coma. Horses that rear up and fall over backwards are particularly prone to damage along the lower surface of the brain. This is because momentum tends to carry the falling horse backwards while that force is counteracted by strong muscles running up the neck to insert onto the basisphenoid bone that serves as the floor of the bony cavity protecting the brain. The end result can be fracture of the skull or, even if the bone remains intact, the forces can lead to major haemorrhage from the large venous sinus that is located between the brain and the skull. Basisphenoid fracture can be suspected if there is leakage of cerebrospinal fluid from the ear. Horses with major brain trauma may have fixed dilated pupils. It is also possible that skull fracture can damage the optic nerves causing blindness. Not every case of skull trauma is quite so devastating. The brain is encased with bone and therefore it is essential that brain swelling be reduced. Initial first aid for brain swelling includes the administration of anti- inflammatory drugs and anti- oxidants. Intravenous infusions of drugs to draw fluid out of the brain and, if there is no bony damage or major haemorrhage, clinical signs which have developed dramatically can disappear very rapidly. Early intervention is critical - call your Equine Brain Disorders VET PROFILE B Vet Watch The brain can be divided into three broad regions: the cerebral cortex or forebrain, cerebellum and brain stem. This horse has sustained trauma to its brain by rearing over backwards and there is massive haemorrhage along the lower surface of the brain. Following the fall, the horse immediately seizured and then lost consciousness. Trauma at the poll often leads to damage to the lower aspect of the brain, and the brainstem in particular. This is because the backwards force generated in the fall is counteracted by strong muscles running up the neck attaching to the basisphenoid bone on the floor of the skull creates fracture at a weak point in this bone. Leakage of cerebrospinal fluid via the ear is suggestive of skull fracture. Horses with severe brain trauma may have loss of consciousness and fixed dilated pupils, in this case due to poll trauma and basisphenoid fracture. ? ? in adult horses By Celia M Marr, Rossdales Equine Hospital and Diagnostic Centre, Newmarket CONTINUED OVER THE PAGE
Transcript of HEALTH & WELFARE VET t Equine Brain Disorders · neonatal intensive care and medical imaging. She...
Presented by
ROSSDALESEQUINE
HOSPITALCotton End Road, Exning,
Newmarket CB8 7NN,Tel: 01638 577754
www.rossdales.com
Celia M Marr BVMS,MVM, PhD, DEIM,DipECEIM, MRCVSCelia is a European andRCVS Specialist in EquineInternal Medicine and workswith both inpatients andoutpatients with medicalproblems at RossdalesEquine Hospital, where sheis responsible for internalmedicine and cardiology.Her clinical and researchinterests are incardiovascular medicine,internal medicine, adult andneonatal intensive care andmedical imaging. She haspublished over 50 researchpapers and educationalmaterial relating to a rangeof medical disorders of thehorse, concentrating oncardiovascular disease anddiagnostic methods inmedical disorders includingediting a book onCardiology of the Horse, thesecond edition of which waspublished in 2010.Celia is an HonoraryProfessor of the Universityof Glasgow, Editor-in-Chiefof Equine VeterinaryJournal, and Chairman ofthe Veterinary AdvisoryCommittee of the HorseraceBetting Levy Board.
HEALTH & WELFARE
rain diseases are veryuncommon in horses.Figures on the exactprevalence are not
available but review of recentcases seen by the medicalteam at Rossdales EquineHospital suggest that just over0.5% of horses admitted forcomplex medical problemshave disorders of the brain.There are a number of importantinfectious diseases worldwide thatcan affect the equine brain but weare fortunate that currently in theUK these diseases are notendemic. The two most commoncauses of equine brain disease inthe UK are head trauma and agroup of diseases that togetherare classified as metabolicencephalopathy. Occasionallyhorses suffer from epilepsy,although not as often as dogs.Meningitis is mainly a disease ofthe young and very rarely, we seeyoung horses which congenital ordevelopmental problems.
Anatomy and functions of thebrainIn simple terms, the brain can bedivided into several regions:• The forebrain or cerebral cortex
is where consciousness residesand this area is responsible forperception, informationprocessing and voluntary controlof movement. Damage to thisarea leads to change inbehaviour, loss or reduction inconsciousness and can lead tocentral blindness – where thesignals are coming in from the
eyes but the brain is not capableof processing that information.
• The cerebellum sits behind thecerebral cortex and provides finecontrol and co-ordination ofmovement.
• The brainstem serves as a bridgewith interconnecting neuraltracts coming down from thecortex and cerebellum andleaving towards the spinalcolumn. This is also wherespecialised areas called cranialnerve ganglia are located. Theseare groups of cell bodies fromthe cranial nerves forminterconnections critical to theircontrol. These cranial nervesinclude the trigeminal and facialnerves which co-ordinatesensation and movement of theface, and the vestibular gangliathat controls the position of thehead, eyes and trunk relative togravity. Damage in this area cancause loss of muscles of thecheek which compromisesswallowing, loss of muscle tone
around the lips, ear and eyelid,and if the vestibular system isdamaged, the horse will developa head tilt and loose its balance.Vestibulospinal tracts integratewith the spinal column anddisruption of these criticalconnections affects the horse’sgait.
Brain TraumaHorses are prone to trauma andwhen this involves the head, theconsequences can be particularlydevastating. Clinical signs canrange from mild disorientationthrough to seizures, profounddepression or coma. Horses thatrear up and fall over backwards areparticularly prone to damagealong the lower surface of thebrain. This is because momentumtends to carry the falling horsebackwards while that force iscounteracted by strong musclesrunning up the neck to insertonto the basisphenoid bone thatserves as the floor of the bony
cavity protecting the brain. Theend result can be fracture of theskull or, even if the bone remainsintact, the forces can lead tomajor haemorrhage from thelarge venous sinus that is locatedbetween the brain and the skull.Basisphenoid fracture can besuspected if there is leakage ofcerebrospinal fluid from the ear. Horses with major brain traumamay have fixed dilated pupils. It isalso possible that skull fracturecan damage the optic nervescausing blindness. Not every caseof skull trauma is quite so
devastating. The brain is encasedwith bone and therefore it isessential that brain swelling bereduced. Initial first aid for brainswelling includes theadministration of anti-inflammatory drugs and anti-oxidants. Intravenous infusions ofdrugs to draw fluid out of thebrain and, if there is no bonydamage or major haemorrhage,clinical signs which havedeveloped dramatically candisappear very rapidly. Earlyintervention is critical - call your
Equine Brain DisordersVET
PROFILE
BVetWatch
The brain can be divided into three broad regions: the cerebral cortex or forebrain,cerebellum and brain stem. This horse has sustained trauma to its brain by rearing overbackwards and there is massive haemorrhage along the lower surface of the brain.Following the fall, the horse immediately seizured and then lost consciousness.
Trauma at the poll often leads to damage to the lower aspect of the brain, and thebrainstem in particular. This is because the backwards force generated in the fall iscounteracted by strong muscles running up the neck attaching to the basisphenoidbone on the floor of the skull creates fracture at a weak point in this bone.
Leakage of cerebrospinal fluid via the earis suggestive of skull fracture.
Horses with severe brain trauma mayhave loss of consciousness and fixeddilated pupils, in this case due to polltrauma and basisphenoid fracture.
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in adult horsesBy Celia M Marr, Rossdales Equine Hospital and Diagnostic Centre, Newmarket
CONTINUED OVER THE PAGE
vet immediately if you suspectyour horse may have sustainedbrain trauma so that first aid canbe instituted. Although it may seem importantto identify the extent of bonedamage using CT or radiography,moving the injured horse to anappropriate medical facility forfurther diagnostic tests can bevery challenging. Often it is morepractical to administer first aid athome and if clinical signs improvein the first 24–72 hours, the horsecan be moved at that time to gaininformation that will help your vetto provide a more accurateprognosis for the long-termoutcome.
Metabolic encephalopathyThe term metabolicencephalopathy refers to a groupof problems where diseaseoutside the brain is causingchemical changes in the body thatare affecting brain function. Thebest recognised is liver failure. Theliver has many functions, whichincludes removing toxic
substances from the body.Bacteria within the gut produceammonia and other chemicalsthat mimic the effects of naturalneurotransmitters. If the liver isnot able to perform this function,levels of these chemicals in thebloodstream rise and this in turn,affects brain function. Althoughthe underlying liver disease mayhave a slow progression, hepaticencephalopathy usually comes onvery rapidly so the problem seemsvery acute. Horses with hepaticencephalopathy are profoundlydepressed, they press or lean theirheads on walls, they can staggeraround and show centralblindness. Additional signs of liverdisease such as weight loss maybe present and the falseneurotransmitters can also affectother nerves in the body (outsidethe brain) so that there may beparalysis of the larynx withobstruction to breathing, gaitabnormalities and sometimescolic due to paralysis of the
stomach.The onset of neurological signs ina horse with liver disease is a poorprognostic sign. However, if theunderlying liver disease isamenable to treatment, around50% of cases will recover. Theonset is rapid, and veterinaryattention should be soughtimmediately. If laryngeal paralysisis present, an emergencytracheotomy with insertion of atube to allow airflow can belifesaving. Horses can be givenvarious drugs, which will helpreduce absorption of chemicalsfrom the gut and counteract theireffects.Similar signs are occasionally seenwith intestinal disease. Damage tothe intestinal wall allows entry tothe bloodstream of largequantities of chemicals thatwould normally be containedsafely in the intestine. Again thesigns are dramatic, but withappropriate veterinary treatment,the prognosis can be excellent, soit is essential that the horse owneris patient and allows the horsetime to recover from what mightseem a very serious problem.Admission to an equine hospital ifoften necessary to provideintensive care but the results canbe good and setting a target ofaround 3–7 days for signs ofrecovery to be evident is realistic.
EpilepsyEpilepsy is the medical diagnosisreached when horses haveintermittent seizures (or fits) butin between the horse is apparentlyhealthy and physical examinationby a veterinarian reveals noabnormality. Seizures can takemany different forms and may bepartial or complete: the signs are
centred on the head and can besubtle - a seizure may simply beinvoluntary twitching andgrimacing of the lips. As theyincrease in intensity there can beear twitching, twisting of the neckthrough to circling and spinningof the whole body and mostdramatically the horse falls over itslimbs and can paddle violently.They can last only a few secondsthrough to almost continuousseizure activity.There is great potential for peoplearound these horses to be injuredand it is essential that where ahorse is known to have had aseizure in the past, everyone whomay come in contact with thathorse understands thatattempting to restrain the horse ispointless because it will not stopseizure activity. It is also very
dangerous as the horse iscompletely unaware of what it isdoing and can easily kick out orotherwise injure bystanders. It isbest to stand back and wait untilseizure activity ceases no matterhow much damage the horse isdoing to itself and itssurroundings. Clues that thehorse may have had a seizurewhile unobserved includeunexplained injury or damage toits stable.Appropriate investigations foradult horses that are seizuring areto use blood tests to rule out liverdisease or other illness elsewherein the body. It is very helpful if theactivity can be documented oncamera, and very achievablenowadays as many people have asmartphone in their pockets. Thiswill allow your vet to confirm thata seizure has occurred and thehorse is not showing other signssuch as sleep deprivation orfainting, which may suggest acardiac problem. Most horses withintermittent seizures do not haveany primary structural
abnormalities of the brain butoccasionally seizures can be thefirst sign of a lesion such as brainabscess. In this case, the seizuresmay be frequent andaccompanied by other clinicalsigns. MRI is the most appropriateadvanced imaging modality toinvestigate seizures because itshows the soft tissues within thesubstance of the brain moreclearly than CT (which is superiorfor bone).
Seizures can damage the brainand promote more seizurestherefore it is helpful if the seizureactivity can be suppressed. Drugssimilar to those in humans withepilepsy can be used in horses tocontrol seizures. However, horseowners should think very carefullybefore commencing therapy. Evenif seizure frequency is reducedconsiderably there is never aguarantee that occasional seizureswill not continue and the drugsused to treat seizures generallyhave a sedative effect so it maynot be appropriate to ride a horsethat is receiving thesemedications. Ultimately this is adecision that the horse ownermust make himself or herselfweighing up the practicality ofkeeping a horse that requires dailymedication and close supervisionthat is dangerous to ride.
ConclusionAlthough the equine brain isvulnerable to trauma and initialsigns of brain disease can bedramatic, with appropriate andprompt first aid, horses can makeremarkable recoveries from braindisorders. The advanced imagingmodalities CT and MRI areimportant tools for reaching adiagnosis.
HEALTH & WELFARE
Damage to the optic nerve is an alternative cause of dilation of the pupils. This horsehas sustained a complex fracture to the skull that includes a fracture line that hassevered the optic nerve as it exits the skull towards the eye.
This horse sustained brain trauma duringa fall while exercising. His initial responseto first aid was excellent but he was leftwith an abnormal eye position.
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CT is the most sensitive imaging technique for bone damage. A CT scan performed sometime after the initial trauma showed that there is damage to the bone around the pathof the abducens nerve which controls one of the muscles which functions to control theeye position and movement. The arrows indicate where the bone has enlarged andcompressed the nerve.
This pony mare shows signs of metabolicencephalopathy, she is fairly unaware ofher surroundings and pays no attentionto her handler how is struggling to stopher stumbling forwards.
After five days of intensive care, the ponymare has made a full recovery and isbehaving normally.
Seizure activity generally starts around the lips: this gelding is grimacing, his ears aretwitching and his head and neck are twisting, all signs of the onset of a seizure.
MRI is the optimal tool for imaging thesoft tissue of the brain. In this case ofidiopathic epilepsy, the arrow pointstowards a brain infarct. This could be theunderlying cause of epilepsy but it isequally possible that this lesion hasarisen secondary to a previous seizureepisode.
