Holly Nash, DVM, MS
Veterinary Services Department, Drs. Foster & Smith, Inc.

Disseminated Idiopathic Myositis (DIM), also known as "Polymyositis," is a "new" disease in pet ferrets. Myositis, or polymyositis, is an inflammation of the muscles. "Disseminated" means it is widespread throughout the body. "Idiopathic" means we, at present, do not understand the cause.

What causes disseminated idiopathic myositis in ferrets?

Ferret owners and veterinarians are frustrated with DIM. Although research on the disease has been ongoing since it was first described in 2003, the cause of DIM is still unknown and the disease process is poorly understood. There have been over 85 suspected cases with approximately half having been confirmed with a microscopic examination of tissues.

DIM may be an immune-mediated disease, meaning the body may be attacking itself. Genetics and infectious organisms are also currently being investigated as potential causes or triggers of this condition. Ferrets suspected of having disseminated idiopathic myositis have been tested for distemper, Aleutian disease virus, feline infectious peritonitis, sarcocystis, and bartonellosis and have been negative for these diseases. Bacterial cultures and sensitivities have been done and have not revealed any bacterial cause for DIM. Electron microscopy and virus isolation results have also been negative.

Ferrets diagnosed with DIM had been on various diets, including several different ferret and cat or kitten foods.

Vaccine histories were obtained for most of the ferrets diagnosed with DIM. Some had received a rabies vaccination and the recommended series of distemper vaccinations. Several ferrets had received only the distemper vaccination that was initially given to them when they were between 4 and 7 weeks of age at the breeding facility. Although all confirmed DIM ferrets received at least one distemper vaccination, there is currently no direct evidence indicating that there is an association between vaccines and DIM. All pet ferrets should continue to be vaccinated for distemper and rabies as recommended.

Which ferrets most commonly acquire disseminated idiopathic myositis?

Disseminated idiopathic myositis affects young ferrets, usually less than 18 months of age; however, there have been a few ferrets over 2 years of age confirmed to have DIM. Both male and female ferrets are susceptible to DIM, and there is no apparent correlation with coat color. Ferrets diagnosed with DIM have been from a variety of breeders, and almost all of the DIM ferrets were spayed or neutered and descented at the breeding facility.

What are the symptoms of disseminated idiopathic myositis?

The signs of disseminated idiopathic myositis are usually acute (come on rapidly). Owners often report that their ferret was normal one day and then had signs of DIM the next. Initial signs of DIM are variable but commonly include: Other signs that are often observed (especially as the disease progresses) include: elevated respiratory and heart rates, dehydration, clear discharge from the nose (and sometimes the eyes), depression, nausea, and skin or coat changes, such as orange dots or abrasions. Ferrets with DIM often seem to be in pain when they are touched on the back or hind end. A veterinarian may detect a heart murmur in a ferret with DIM. Although signs of DIM usually come on relatively quickly, the duration of the illness can be days to weeks, or even months. So far, all confirmed DIM cases have died or been euthanized.

What are the common laboratory test results in ferrets with disseminated idiopathic myositis?

Although the white blood cell count may initially be normal, it often rises dramatically within 7-10 days of onset of the symptoms of DIM. Ferrets with DIM are usually mildly to moderately anemic. Glucose levels are frequently elevated. Alanine aminotransferase (ALT) (a liver-specific enzyme) is elevated in some ferrets. Interestingly, creatine kinase (CK), an enzyme that is usually elevated when there is damage to muscle tissue or severe inflammation of the muscle, is NOT elevated in ferrets with DIM.

Except for an occasional ferret who has had an enlarged spleen or abdominal lymph node, x-ray and ultrasound results are usually normal. Exploratory surgeries usually do not reveal any significant abnormalities. Special stains for protozoa and fungi have been negative. The urine of some ferrets with DIM has had a high pH (7-8). Crystals, blood and protein have been present in several cases, and a few ferrets with DIM have had urinary tract infections. The relevance and significance of these urinary findings is unknown.

What are the common biopsy results in ferrets with disseminated idiopathic myositis?

Biopsies of enlarged lymph nodes and muscle tissue reveal severe, widespread inflammation, often with pus present. Not every muscle is affected, so some ferrets with DIM will occasionally have a negative muscle biopsy.

What are the common postmortem findings in ferrets with disseminated idiopathic myositis?

Microscopic evaluation of tissues taken after death show severe inflammation of muscle tissue. Skeletal muscle, cardiac (heart) muscle, and smooth muscle (muscle found in the digestive tract), may all be abnormal, with the esophagus being particularly affected. Non-muscular organs such as fat, brain, liver, lung, spleen and bone marrow have also been affected. Testing has been negative for infectious organisms (cultures, special stains, electron microscopy, and virus isolation), including rabies.

How is disseminated idiopathic myositis in ferrets diagnosed?

A tentative diagnosis is based on physical signs and laboratory results (see above). A definitive diagnosis in a living ferret will most likely be obtained with a biopsy of skeletal muscle; samples most indicative of DIM from a deceased ferret are esophagus, heart, and skeletal muscle.

How is disseminated idiopathic myositis in ferrets treated?

There is currently no known treatment for DIM. One characteristic of ferrets with DIM is a general lack of response to treatments. Some ferrets have temporarily improved with certain medications, but it is unknown whether it was a true response to a drug or a temporary spontaneous remission. Supportive care is currently recommended (e.g. supplemental feedings and fluids) and antibiotics may help prevent secondary bacterial infections.

What is the prognosis for ferrets diagnosed with disseminated idiopathic myositis?

Although all of the ferrets confirmed to have DIM have ultimately died, there are a handful of potential survivors. Unfortunately, although several suspected cases appear to have responded to medical therapy, prior biopsies were never done to confirm that these ferrets ever had DIM. These cases are being thoroughly investigated. Although there is no known definitive treatment for DIM, there are experimental treatment options available.

What should I do if I think my ferrets may have disseminated idiopathic myositis?

If you suspect your ferret has DIM, contact your veterinarian as soon as possible. You may also write to DIMFerrets@yahoo.com if you have a suspected case. For more information, please visit the American Ferret Association website: http://www.ferret.org/.



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