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PEER REVIEWED 40 JULY/AUGUST 2018 warranted; there is no evidence to support the use of nonsteroidal anti-inflammatory drugs or corticosteroids. Hypothyroidism Hypothyroidism has been implicated as a cause for both peripheral and central vestibular disease in dogs. The pathogenesis of hypothyroid-associated vestibular disease has been described as a component of polyneuropathy or as myxedematous disease causing nerve compression (cranial nerve VIII and sometimes cranial nerve VII) as they exit the skull through the internal acoustic meatus. 2,9 Accordingly, patients that present with cranial nerve VII and VIII dysfunction should have their thyroid function evaluated. Thyroid hormone supplementation typically results in improvement within a few months. Ototoxicity Peripheral vestibular signs may develop if the ear has been flushed with any routine cleaning solution if the tympanum is ruptured. Many drugs/agents are potentially ototoxic; dogs may develop signs of peripheral vestibular disease or deafness. Clinical signs of vestibular disease may develop rapidly (as soon as 10 minutes). Within 3 days to 3 weeks, central compensation results in gradual improvement of clinical signs; the compensation is maximal after about 3 months. The head tilt, however, may still be obvious and permanent. Chlorhexidine solutions can significantly contribute to ototoxicity and should be avoided if the status of the tympanum is unknown. Aminoglycoside antibiotics (parenteral or topical) can affect the hair cells, flocculonodular lobe and fastigial nucleus; streptomycin tends to have vestibular effects, whereas neomycin, gentamycin, kanamycin, and vancomycin tend to have more effect on the auditory system. In addition, loop diuretics, cisplatin and propylene glycol have also been implicated as potentially ototoxic. Central/Paradoxical Vestibular Disease Meningoencephalitis of Unknown Etiology (MUE) MUE encompasses several presumed idiopathic noninfectious inflammatory diseases in dogs; other terms that fall into this grouping include: FIGURE 3. Photograph of canine Horner's syndrome in the right eye. Note the elevated third eyelid, miosis and mild ptosis. Enophthalmos, which is often present, is not appreciated in this photograph. FIGURE 4. Post-contrast axial image of the canine brain at the level of the caudal brainstem. Note the contrast enhancement of the right lateral aspect of the medulla (red arrow). The tympanic bullae (white arrows) show isointense signal and heterogenous contrast enhancement depicting a soft-tissue/high protein type infiltrate in the normally air- filled bullae. Left: Simon R. Platt Though the cause of idiopathic vestibular disease is unknown, there is consideration that the cause may be due to a viral infection of the vestibular nerve. 2

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