Canine Dysautonomia

The dysautonomias are a group of diseases with strikingly similar clinical and pathologic signs reported in a number of unrelated species, including horses, dogs, cats, rabbits, and hares. The disease is characterized by the degeneration of neurons in autonomic ganglia and clinical signs of autonomic nervous system dysfunction. The etiology is unknown in all species, and there is no effective treatment.

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, but the disease has not been diagnosed there for many years. 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 of Canine Dysautonomia

Canine dysautonomia

Image

Courtesy of Dr. Caroline Hahn.

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

• 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 to confirm 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.