This disease is a genetically-based, immunologically-mediated inflammatory disease that primarily affects the skin and, more rarely, the muscle of either immature or adult dogs. In early-onset cases (in immature dogs) the disease often manifests more severely than when the disease becomes apparent in adulthood.
Beyond the understanding of its genetic origin, the cause of dermatomyositis is poorly understood. Interestingly, some veterinary researchers believe that vaccine administration is related to the onset of the disease.
Symptoms and Identification
Skin symptoms are generally more prevalent and severe than those arising from muscle inflammation, when present. These lesions tend to begin focally with hair loss, crusts and ulcers on the face, around the eyes, at the edge of the ears, over pressure points and at the tip of the tail. Lesions in these areas may be confined but they can actually be quite severe. Other dogs may suffer a more generalized version.
When the muscles are affected, it's usually not very obvious. However, in puppies, it can be quite severe. In these cases, muscle atrophy, generalized weakness and even mega-esophagus (as evidenced by regurgitation and/or aspiration pneumonia) can result.
Diagnosis of dermatomyositis is achieved via skin biopsy, primarily. Muscle biopsy and electromyogram studie (to determine whether nerve conduction abnormalities affect the muscles) will sometimes be undertaken in more severely affected dogs.
This disease is seen almost exclusively in Shetland Sheepdogs and other Collie breeds. The mode of hereditary transmission is autosomal dominant, with variable expression.
Drug treatment for this disease can include pentoxifylline, vitamin E, prednisone, azathioprine or cyclosporine. The efficacy of treatment is highly variable. Some severely affected dogs have had to be euthanized when treatment was unable to help them achieve a comfortable quality of life.
Dermatomyositis can be very expensive to treat given that many of the drug choices are pricey. A minimum of $100 to $200 a month in drugs alone is to be expected for most of these patients. Diagnosis itself is typically a $500 to $1,000 proposition.
Breeding programs must exclude affected dogs and their first degree relatives.
Scott, D.W., Miller, W.H., Griffin, C.E. 1995. Muller and Kirk's Small Animal Dermatology. pp 759-765. W.B. Saunders Co., Toronto.
Ihrke, P.J. and Gross, T.L. 1995. Ulcerative dermatosis of Shetland sheepdogs and collies. In J.D. Bonagura (ed.) Kirk's Current Veterinary Therapy XII Small Animal Practice, p. 639-640 WB Saunders Co., Philadelphia