Canine familial dermatomyositis is a heritable inflammatory disease affecting skin and muscle. It has been seen primarily in the Collie, Shetland Sheepdog and their related croosbreeds. Dermatomyositis-like disease has been reported occasionally in the Chow Chow, Beauceron, Welsh Corgi, Lakeland Terrier, German Shepherd Dog, Miniature Schnauzer, Miniature Dachshund, and Kuvasz. Severely affected dogs show growth retardation, enlarged esophagus, lameness, widespread atrophy (muscle wasting), and have difficulty in grasping or otherwise getting food into the mouth. Infertility is an additional feature of this condition. In Collies and Shetland Sheepdogs, the disease often presents as a severe autoimmune dermatitis of the ears, face, lips, tip of the tail, and over bony prominences of limbs, alopecia, and masticatory myositis (inflammation of the muscles that close the jaw). There is no blood test to identify carriers, and not enough data have been collected to permit pedigree analysis to select good breeding stock.
Signs starts to show at about 12 weeks of age and may look like scrapes on the face, ears, elbows, hocks, and other friction points. In the German Shepherd Dog and Welsh Corgi, paw pads may become swollen. In chronic cases, scarring of the skin occurs. Lesions occur over bony prominences due to susceptibility to trauma. Unless skin ulcers develop, the disease does not cause much pain or itchiness. Extensive exposure to sun may trigger aggravation of the disease. At the early stage of the disease, muscles are involved only lightly.
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Because clinical signs of dermatomyositis are often similar to those of demodicosis, dermatophytosis, facial pyoderma, and discoid lupus erythematosus, the disease is difficult to diagnose. Most cases are diagnosed on the basis of history, clinical signs, electromyography, and biopsy. Skin scrapings are usually performed to rule out demodicosis, while fungal cultures are performed to rule out dermatophytosis. If small number of Demodex mites are found on the scrapings, skin biopsy is performed. Well-chosen biopsies often reveal characteristic changes and electromyographic (EMG) studies may show abnormalities in the muscles as well. There is no cure for dermatomyositis. Therapy is only symptomatic. The inability to diagnose dermatomyositis before clinical symptoms ensue has made control of the disease difficult. Both vitamin E and corticosteroids have been used to relieve scaling and scarring, but neither will cure the condition. In one study, dogs were treated with pentoxifylline. Four of the 10 dogs with familial canine dermatomyositis responded to treatment, and six dogs had a partial recovery. Some animals may recover spontaneously, but they should not be bred, since offspring will undoubtedly be affected, at least to some extent.
- Peter J. Ihrke, Emily J. Walder, Verena K. Affolter, Thelma Lee Gross. Skin Diseases of the Dog and Cat
- Linkage of dermatomyositis in the Shetland Sheepdog to chromosome 35.Clark LA, Credille KM, Murphy KE, Rees CA. Department of Pathobiology, College of Veterinary Medicine and Biomedical Sciences, Texas A+M University, USA
- Rees CA, Boothe DM. Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, Texas A and M University, USA. Therapeutic response to pentoxifylline and its active metabolites in dogs with familial canine dermatomyositis