- Cause : damage to the vestibular system which is responsible for maintenance of the normal orientation of the trunk, limbs and eyes with respect to the position and movements of the head.
- Signs : disturbed equilibrium and ataxia, without paresis.
- Diagnosis : history and clinical signs (exacerbated by blindfolding).
- Treatment : appropriate treatment of the primary cause of the vestibular damage.
- Prognosis : guarded - affected animals often centrally accommodate with time and can return to their previous function, although signs can still be elucidated by blindfolding.
- Head trauma .
- Infectious meningoencephalitides [Equine viral encephalitides] .
- Hepatic encephalopathy [Liver: hepatoencephalopathy] .
- Protozoal myeloencephalitis .
- Verminous encephalomyelitis .
- Mycotoxicosis .
- Brain abscess.
- Tumor Link: CNS: neoplasia (NEW).
- Polyneuritis equi [Cauda equina neuritis] .
- Temporohyoid osteoarthropathy .
- Otitis media/interna .
- Idiopathic vestibular disease.
- Lightening strike.
- All signs are exacerbated by blindfolding the animal.
- Peripheral disease:
- True head tilt towards affected side, ie ventral deviation of the poll to the affected side.
- Spontaneous rotary or horizontal nystagmus with the fast phase away from the affected side.
- Ipsilateral ventrolateral strabismus.
- Head elevation.
- Staggering dysmetric gait with a tendency to lean or circle towards the affected side.
- Extensor hypotonia ipsilateral to lesion.
- Hyperextension of contralateral limbs.
- Asymmetrical ataxia.
- Malfunctioning righting reflex → exaggerated attempts to stand.
- Clinical signs of cranial nerve VII dysfunction if concurrently affected. Twisted muzzle, droopy ear, corneal ulcer, inability to shut eye, foul breath due to paralysis of the buccinator muscle.
- Clinical signs of cranial nerve VIII and IX in cases of skull fracture secondary to temporohyoid osteoarthropathy.
- Difficulty in eating.
- Central disease:
- Variable nystagmus: horizontal, rotatory or vertical.
- General proprioceptive deficiencies.
- Head tilt towards or away (rare) from lesion.
- Frequently adjacent brainstem structures are involved → other signs:
- Severe, more symmetric, ataxia.
- Wide, swinging head movements.
- Deafness if cochlear branch of cranial nerve VIII is involved bilaterally.
- Guarded: affected animals often centrally and visually accommodate with time and can return to their previous use, although vestibular function deficits can still be elucidated by blindfolding.
- If blindness is present the prognosis worsens because of the loss of visual compensation for vestibular malfunction.
- Associated facial and other cranial nerve deficits often remain, with only slight improvement over time. If even mild improvement of facial nerve function is noted in the first 4 months, full function may return.
- Early removal of toxic fodder can → a complete recovery from mycotoxicosis over a period of a few days to several weeks.
Extreme care should always be taken when riding animals with vestibular disease: reduced light situations can instigate a rapid return of clinical signs or cause increased anxiety in the horse, which could be dangerous to the rider.
Expected response to treatment
- Affected animals often centrally accommodate with time.