Page 1069 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1044 CHAPTER 10

VetBooks.ir Table 10.1 Common breed predispositions for neurological diseases in horses

AETIOLOGY AND DIAGNOSTIC
BREED(S) DISEASE PRESENTING SIGNS TESTING
Arabian Juvenile idiopathic Self-limiting idiopathic epilepsy of Arabian Unknown, but possibly autosomal
epilepsy foals (median 2 months of age) with dominant mode of inheritance
generalised tonic–clonic seizures
Arabian Lavender foal Congenital episodic tetany where Autosomal recessive gene (MYO5A)
syndrome recumbent foals develop extreme rigidity linked to coat colour (lavender or
and opisthotonus when stimulated or silver hue to coat). Genetic testing
trying to right themselves. Never capable available commercially
of standing unassisted
Arabian (also seen in Cerebellar Signs appear from birth or within a few Post-natal degeneration of Purkinje
Welsh, Trakehner and abiotrophy months and include head and neck sway, cells due to an autosomal recessive
Bashkir Curly horse) loss of menace response, spasticity, rearing genetic mutation of the TOE1/MUTYH
with extended forelimbs when handled, and gene. Genetic testing available
an intention tremor of the head commercially
Arabian (Appaloosa, Occipitoatlantoaxial Familial OAAM of the Arabian horse is Deletion of a focus near HOXD3 may
Friesian, miniature malformation associated with occipitalisation of the atlas be responsible for Arabian OAAM
horse, Quarter horse (OAAM) and atlantalisation of the axis, which are
are also fused together with connective tissue.
overrepresented) Signs reflect compression of the cervical
spinal cord with severe tetraparesis, ataxia
and extended head and neck posture
Friesian Hydrocephalus Stillborn or weak foals that die shortly after Distension of the ventricular system in
(Thoroughbred, birth with gross enlargement of or the brain due to jugular foramen
miniature horse and dome-shape to the head. Dystocia may narrowing. Autosomal recessive
Standardbred also have been present inheritance associated with a
overrepresented) nonsense mutation in B3GALNT2
Miniature horse Narcolepsy Idiopathic narcolepsy Presumed inherited characteristic
amongst miniature horses but
unknown genetic basis at this time

Focal seizures are localised involuntary move- assessed. Subtle behavioural changes may only be
ments and are not usually associated with a change apparent in well-handled horses by their routine car-
in the state of consciousness. They are recognised as ers, and may not have been detected at all in those at
focal and asymmetrical muscle spasm or fasciculation. field rest, or in young, unbroken horses.
Occasionally, horses displaying signs of a focal seizure Scoring systems exist for human patients with
go on to develop a ‘secondary’ generalised seizure, suspected hepatic encephalopathy, dementia or an
because the cerebral cortex focus responsible for the altered state of consciousness. Regretfully, there are
former spreads through the cortex and results in gen- no equivalent scoring systems for horses and there-
eralised signs. These include a loss of consciousness fore it is only with the benefit of hindsight, once obvi-
and involuntary muscle activity such as limb flailing, ous behavioural abnormalities are present, that horse
nystagmus and passage of urine and faeces. owners may remember subtle changes in their horse’s
behaviour. Sometimes the behaviour associated with
PHASE 2 – OBSERVATION cerebral disease is clearly bizarre and abnormal, such
as head-pressing, or compulsive biting, licking or
Initially, the horse should be observed from a walking. Horses with unilateral cerebral lesions that
distance so that mental status and behaviour can be circle tend to walk towards the side of the lesion.