Canine Dysautonomia FAQ's

What is dysautonomia? Dysautonomia may be defined as a malfunction of the autonomic nervous system. The autonomic nervous system, composed of the sympathetic and parasympathetic branches, is responsible for involuntary visceral functions such as contraction of smooth muscles, the pupillary light reflex, and heart rate. Dysautonomia causes degeneration of the nerve cells and ganglia that make up this part of the nervous system. The result is a wide variety of neurological problems in several different body systems.

Where does dysautonomia occur? Canine dysautonomia was first diagnosed in the United Kingdom. Several cases have also been reported in other European countries. In the United states, most of the affected dogs have been from western Missouri and eastern Kansas. A few cases have also been diagnosed in western Tennessee, Oklahoma, Colorado, and Wyoming.

How common is canine dysautonomia? We don't know for sure how common dysautonomia is. Since 1994 , 5-9 cases have been referred to the University of Missouri's Veterinary Teaching Hospital each year. This added up to a total of 42 cases seen here through January of 2000. A study is currently underway to try to estimate the number of cases that practicing veterinarians are seeing across the state.

What causes dysautonomia? The cause of dysautonomia has not yet been determined. Equine dysautonomia has been recognized as a disease of horses in the United Kingdom since the early 1900's, but no etiologic agent has ever been proven. Arguments have been made for both infectious and toxic causes. Most researchers seem to favor the idea of a toxin because of the nature of the pathology and the lack of horizontal transmission. Most of the dogs diagnosed with dysautonomia in Missouri have come from a rural, outdoor background. 

What are the clinical signs associated with dysautonomia? Ocular signs that are common to most dogs with dysautonomia are: mid-range or dilated pupils that are not responsive to light, decreased tear production, and elevated third eyelids. Vomiting and regurgitation are also frequently seen because of a decrease in esophageal and intestinal motility. Dysautonomia patients often have difficulty producing a coordinated stream of urine, and anal sphincter tone is decreased in the majority of cases. Generalized weakness and dry mucous membranes are also typically present.

What is the treatment for dysautonomia? Treatment for canine dysautonomia consists mostly of supportive care. Fluid therapy may be indicated in dehydrated animals. Bethanechol and metoclopramide have been used to improve micturition and intestinal motility. In most cases, however, these drugs have been of limited benefit.

How is dysautonomia diagnosed? A clinical diagnosis is often made based on the presence of clinical signs that are typical of this disease. There are a couple of ancillary diagnostic tests that may be helpful in making the diagnosis. Instillation of dilute (0.05-0.1%) pilocarpine drops in the eye of an affected dog will usually result in pupillary constriction within about 30 minutes. Some normal dogs can also respond to this concentration of pilocarpine, although it usually takes them 45-60 minutes. A subcutaneous injection of low-dose bethanechol (0.0375 mg/kg) can also be used to see if it improves the dog's ability to urinate. Neither of these tests are specific for dysautonomia, but they can be used to rule-out an inability of the iris and detrusor muscles to respond to acetylcholine. Histologic examination of autonomic ganglia by a qualified pathologist is the best way to confirm a diagnosis of dysautonomia.

What is the prognosis for dogs with dysautonomia? Over 90% of the dogs with dysautonomia seen at the University of Missouri have either died or been euthanized within a few days to weeks after diagnosis. Most dysautonomia patients develop a rapidly progressive and disabling disease. A couple of dogs have survived long-term (i.e. greater than 6 months). Surviving dogs were those that had a milder clinical course of the disease.

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