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FEATURES JULY/AUGUST 2018 39 Peripheral Vestibular Disease Otitis media/interna Of the peripheral vestibular diseases, otitis media/ interna (OMI) is the most common diagnosis.4,5 Though all breeds can be affected, in one study, the most commonly affected breeds were French bulldogs, cavalier King Charles spaniels, cocker spaniels and West Highland white terriers. 5 Diagnosis is based on otoscopic examination, imaging (CT or MRI is preferred 4,5 ) and culture via myringotomy. It is important to note that an intact tympanic membrane does not rule out OMI; in fact, infection most commonly results from (1) a descending infection from otitis externa, (2) hematogenous spread of microorganisms or (3) extension of microorganisms from the pharynx via the auditory tube. A very common clinical presentation of OMI is vestibular disease with concurrent cranial nerve VII dysfunction and/or Horner's syndrome ( FIGURE 3 ), due to the coursing of these pathways through the middle ear ( FIGURE 2 ). Treatment is antibiotic therapy, ideally based on culture and sensitivity, and supportive care. An uncommon but severe progression of OMI is intracranial infection resulting from central extension of bacteria into the brainstem ( FIGURE 4 ). Recognition and prompt treatment of this complication can result in a good prognosis for recovery.6 Idiopathic Vestibular Disease Idiopathic vestibular disease is reported to be the second most common cause of peripheral vestibular disease in the dog.7 Classically, no other neural deficits besides vestibular dysfunction are present (i.e., cranial nerve VII or Horner's); however recently an idiopathic syndrome of concomitant facial nerve and vestibular neuropathy was described in 16 dogs.8 The average age of dogs that develop idiopathic vestibular disease is 12 to 13 years and there is no breed or sex predilection. There is typically a peracute onset with affected animals showing clinical improvement within a few days and near complete resolution within 3 to 4 weeks.7 Occasionally, severely affected dogs will maintain a persistent head tilt despite otherwise complete resolution of all other vestibular signs. 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 In cases where the onset is peracute and there are no other cranial nerve abnormalities, the likelihood of idiopathic vestibular disease is high and only symptomatic treatment is TABLE 2 Differential Diagnoses of Head Tilt in Dogs PERIPHERAL CENTRAL Degenerative — Storage disease Anomalous Congenital vestibular disease (rare) Hydrocephalus, Chiari-like malformation Metabolic Hypothyroidism Hypothyroidism Neoplastic Vestibular nerve sheath tumor, otogenic neoplasia Intracranial neoplasia — primary vs. metastatic Nutritional — Thiamine deficiency Idiopathic Geriatric ("old dog") vestibular disease — Infectious/Inflammatory Otitis media/interna Viral: canine distemper virus; Bacterial: Rocky Mountain spotted fever, bartonellosis, ehrlichiosis, anaplasmosis, otogenic extension into the brain; Protozal: toxoplasmosis, neosporosis; Fungal: cryptococcosis, coccidioidomycosis, blastomycosis, others Non-infectious: Meningoencephalitis of Unknown Etiology (MUE/GME) Toxic Ototoxic drugs Metronidazole Trauma Petrous temporal bone Brainstem/cerebellum Vascular — Ischemic or hemorrhagic vascular accident (brainstem/cerebellum); hypertension

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