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Canine Dysautonomia

By Caroline N. Hahn, DVM, MSc, PhD, DECEIM, DECVN, MRCVS, Senior Lecturer in Veterinary Clinical Neuroscience, Royal (Dick) School of Veterinary Studies, University of Edinburgh

Canine dysautonomia is a degenerative polyneuropathy characterized by neuronal degeneration within the autonomic, somatic, central, peripheral, and/or enteric nervous system causing multisystemic effects similar, if not identical, to the dysautonomia in horses, cats, rabbits, and hares. Canine dysautonomia was first described in England in 1983, and there have been no new cases reported in the past decade. Although individual cases have been reported in Scotland, Norway, Belgium, Germany, and Greece, canine dysautonomia is less commonly reported in Europe than in the USA, with higher numbers primarily in the Midwest. In the USA, risk factors were reported to include a rural habitat and spending >50% of the time free outdoors.

Clinical Findings:

The most consistent history and physical examination findings are acute-onset vomiting, diarrhea, mild obtundation, inappetence, reduced or absent anal tone, absence of pupillary light responses and lacrimal secretion, mydriasis, and protrusion of the nictitating membrane. Secondary effects of autonomic dysfunction, such as aspiration pneumonia and lethargy, may develop. Weight loss is often dramatic.

Laboratory findings are nonspecific. Pharmacologic testing of the pupils is probably the best single test for confirming the diagnosis. Dilute pilocarpine (0.05% ophthalmic solution) results in rapid pupillary constriction in dogs with dysautonomia because of supersensitivity of the denervated muscle to cholinergic drugs. The prognosis is grave.