15 Head tilt and nystagmus
The vestibular system is responsible for balance and coordinating movements of the eyes, trunk and limbs with changes in head position. Head tilt and nystagmus are typically associated with unilateral vestibular disease and are relatively common presenting signs in canine emergency patients. Jerk nystagmus is typical of vestibular disease with the slow (pathological) phase towards the side of the lesion and the fast (corrective) phase away from the side of the lesion. Occasionally animals present with nystagmus due to cerebellar disease (paradoxical vestibular disease) or abnormalities in visual pathways. Other clinical signs associated with vestibular disease are listed in Box 15.1.
Vestibular disease may be the result of a lesion affecting either the central or the peripheral component of the vestibular system.
The central component of the vestibular system is located in the brainstem and cerebellum. Nystagmus in central vestibular disease can be horizontal, rotatory, vertical or positional, with the fast phase towards or away from the lesion. Affected animals may well have additional clinical signs that reflect brain involvement, such as reduced mentation from depression through to coma, or ipsilateral paresis and proprioceptive deficits.
The peripheral components of the vestibular system are sensory receptors in the inner ear and the vestibular portion of vestibulocochlear nerve. Nystagmus in peripheral vestibular disease can be horizontal or rotatory, with the fast phase away from the side of the lesion. Affected animals may have normal mentation or they may be markedly disorientated; signs of brainstem abnormality are not expected unless there has been extension of inner ear disease. Paresis and proprioceptive deficits should not occur.
Horner’s syndrome (third eyelid protrusion, pupillary constriction, drooping of upper eyelid, enophthalmos) and facial nerve deficits (including ipsilateral drooping of and inability to move ear and lip, widened palpebral fissure, absent blinking) may occur with peripheral vestibular disease but are typically not recognized in the idiopathic form.
Paradoxical vestibular disease refers to a syndrome of nystagmus, head tilt and circling due to cerebellar disease. Head tilt and circling occur contralateral to the side of the lesion and there are usually other more typical signs of cerebellar disease (e.g. head tremor, ipsilateral dysmetria).
The most common causes of central vestibular disease are brain tumours and inflammation (infectious or noninfectious). Trauma and metronidazole intoxication are other causes.
The most common causes of peripheral vestibular disease are otitis media or interna, and idiopathic vestibular disease. Ototoxicity (e.g. due to topical medications), middle or inner ear trauma or tumours, and hypothyroidism are other possible causes. Nasopharyngeal polyps can cause peripheral vestibular disease in cats.
Clinical Tip
Signalment may help to raise or lower the index of suspicion for certain differential diagnoses. For example, idiopathic peripheral vestibular disease is seen most often in older dogs and congenital vestibular disease is most likely in very young animals.
As always, a thorough history should be taken in all cases. Important pieces of information include:
In the majority of cases, the neurological system is the only system to be significantly affected. Animals with central vestibular disease due to a primary brain lesion may have potentially significant cardiovascular abnormalities and hyperthermia may be identified in some very disorientated dogs. A range of abnormalities may be identified following trauma.
Bilateral otoscopic examination should be performed in animals with peripheral vestibular signs. The tympanic membrane is often ruptured but if it remains intact it may not be possible to detect fluid in the middle ear. Myringotomy may need to be performed both for diagnostic purposes and to collect a fluid sample for cytology and microbiology. Most animals require heavy sedation or preferably general anaesthesia for a reliable otoscopic examination to be performed.
The emergency database is likely to be unremarkable in a lot of animals with vestibular disease. Dehydration may be identified in some animals and peripheral blood smear examination may reveal leucocytosis in some cases (e.g. otitis media or interna, inflammatory brain disease).
Animals with signs of central vestibular disease require referral for advanced diagnostic imaging (computed tomography or magnetic resonance imaging) and cerebrospinal fluid analysis.
Well-positioned plain radiographs of the skull designed to highlight the tympanic bullae may provide evidence of infection or neoplasia of the middle or inner ear. However, general anaesthesia is required and this should therefore only be undertaken in cases with signs suggestive of peripheral disease. Advanced diagnostic imaging modalities are considerably more sensitive so referral may be appropriate.
Treatment of vestibular disease centres on addressing the underlying disorder if this is possible. For example, administration of toxic drugs should be discontinued and bacterial otitis should be treated with several weeks of systemic antibiosis (preferably based on culture and sensitivity testing).
Supportive care is also required with respect to intravenous fluid therapy in animals that are unable or unwilling to drink. Some dogs may also require assistance for toileting purposes and other nursing measures including well-padded bedding. Symptomatic anti-emetic treatment (maropitant, metoclopramide, ondansetron) is indicated in animals that are vomiting and may also help with nausea.
Animals presenting with head trauma must be stabilized as required (see Ch. 28).