South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Investigation and management of horses with seizures
Piercy RJ*
MA VetMB MD PhD DipACVIM MRCVS
Professor of Comparative Neuromuscular Disease
Royal Veterinary College
Summary
Seizure disorders are amongst the more common of the neurological presentations seen in equine
practice. They are relatively easy to recognise, but it is often difficult to identify their precise
aetiology. Crucially, owners require appropriate advice regarding the safety aspects since a
seizuring adult horse can be extremely dangerous. This presentation will cover the different forms
of seizure seen in horses, in particular the more common, generalised or grand mal form, and the
less-easy to recognise, focal (or partial) seizure, before discussing further investigation and
treatment/management and prognosis.
Classification
Generalised seizures represent cerebrocortical depolarisation that often is initiated in the motor
cortical area that controls the lips and head, before progressing to the neck, trunk and limbs.
Consequently, often horses initially present with tremors or spasm of facial musculature, which
then spreads to the rest of the body, and might involve other involuntary reflexes, such as
urination and defecation. Consciousness might be lost as can posture; in the most severe cases,
the horse enters a state of rhythmic involuntary muscle spasms – status epilepticus – which can
result in musculoskeletal trauma. The ictal phase usually only lasts for a few minutes, but
commonly horses appear sedated, disorientated and are centrally blind for several hours following
an episode before returning to become clinically normal.
Focal seizures arise from a single part of the prosencephalon with clinical signs that depend on
the precise region and the relative spread of depolarisation. These cases can sometimes be hard to
recognise clinically, but they might include horses with facial twitching, isolated muscle
fasciculation or rhythmical or cyclic isolated limb movements. Since motor pathways decussate
below the cerebrum, lesions are located contra-laterally to the body region involved. Occasionally
in horses, focal seizures progress to a generalised seizure.
Diagnosis
Clinicians are often presented with videos or descriptions of horses from worried owners, but
frequently the horse appears clinically normal by the time of veterinary examination; alternatively,
horses might still be in their post ictal phase. All horses should receive a thorough physical
examination and neurological examination. If the latter is abnormal, (between seizure episodes),
in this author‟s experience, there is more likely to be detectable structural brain disease detectable
with advanced imaging (see below). Haematological and routine biochemical investigation is
warranted, including evaluation of ionised calcium and magnesium (especially in pregnant or
lactating mares). Note that many horses have mild elevations (<2000IU/l) in CK and AST for
hours to days following a seizure. However, most horses with histories of seizures are normal on
clinical/neurological examination and with routine use of blood testing. Furthermore, in most
horses with generalised seizures, additional advanced imaging (e.g. magnetic resonance imaging,
computed tomography) is uninformative. Similarly, electroencephalography (EEG) is unlikely to
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