Today's Veterinary Practice

TVP_JUL-AUG2018

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PEER REVIEWED 42 JULY/AUGUST 2018 todaysveterinarypractice.com granulomatous meningoencephalomyelitis, necrotizing meningoencephalitis and necrotizing leukoencephalitis. MUE should be considered in patients that are suspected to have central vestibular disease with a multifocal intracranial localization; for example, vertigo with seizure activity, multiple cranial nerve deficits and/ or concurrent spinal cord dysfunction or pain. Female, small breed dogs 4 to 8 years of age are predisposed, and diagnosis is based on MRI and, cerebrospinal fluid analysis, with or without infectious disease testing. Treatment involves immune suppression with glucocorticoids plus a chemotherapy drug (cytarabine arabinoside, procarbazine) or immunomodulating drug (cyclosporine, leflunomide). Aggressive long-term treatment is necessary, and the prognosis is guarded. 10 Cerebrovascular Disease Head tilt is the second most common clinical sign in dogs with cerebellar vascular infarcts. 12 A cerebrovascular accident (CVA) should be considered high on the differential list in patients that have acute onset, focal and nonprogressive central or paradoxical vestibular signs. Cerebrovascular disease can initially present as a transient ischemic attack (TIA), which is defined as a temporary, focal brain deficit secondary to vascular disease that completely resolves in <24 hours. In a recent study, 22% of the dogs investigated had episodes consistent with a TIA prior to a CVA or stroke. 12 Diagnosis of cerebrovascular disease is based on history, clinical signs and MRI of the brain; most CVAs are easily recognized on MRI; however many cases of TIA are undectable even with high field MRI. 13 Following diagnosis of a CVA or suspicion of TIA, an investigation for the underlying cause should ensue. In one study of 33 dogs with brain infarcts, 18 cases had the following comorbidities identified: hypertension (29%), chronic kidney disease (24%), hyperadrenocorticism (18%) and single cases of aortic stenosis, diabetes mellitus, hemangiosarcoma and pheochromocytoma. 14 Treatment for stroke patients is supportive and many patients (approximately two-thirds) will recover with time; risk of recurrence is significantly higher in those patients in which a predisposing medical condition is identified. 14 Metronidazole Toxicity Metronidazole administration can cause central vestibular or cerebellar dysfunction in dogs, typically following chronic administration of doses that exceed 60 mg/kg q24h. Diagnosis is based on history and clinical signs. Treatment includes cessation of metronidazole therapy and supportive care. It has been shown that diazepam administration (0.5 mg/kg PO q8h for 3 days) significantly reduces recovery time in affected dogs. 11 STEP 3: RATIONAL DIAGNOSTICS AND INITIAL TREATMENT STRATEGY The diagnostic plan, treatment and prognosis can vary to a large extent based on whether the patient has peripheral or central vestibular disease. A careful history should be taken, including rate and duration of onset, whether the signs have progressed since onset, medications administered, diet, travel history, and existence of any other comorbidities. Physical exam should include a complete otoscopic exam and complete neurological examination to determine if the patient localizes to peripheral or central disease. A minimum database, including complete blood count, serum chemistry, blood pressure and thoracic with or without bullae radiographs, are recommended. If systemic infectious disease is suspected, serum titers or polymerase chain reaction for likely organisms ( TABLE 2 ) can be performed. In patients where peripheral vestibular disease is suspected, additional diagnostic considerations may include myringotomy with culture and sensitivity and a complete thyroid panel (thyroxine, free T4 and thyroid-stimulating hormone) based on clinical suspicion. For patients that localize to central vestibular disease or those that are not improving with initial therapy, advanced imaging (ideally MRI) of the head and possible cerebrospinal fluid analysis are highly recommended. A cerebrovascular accident (CVA) should be considered high on the differential list in patients that have acute onset, focal and nonprogressive central or paradoxical vestibular signs.

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