Canine familial dermatomyositis (DM) is an inheritable inflammatory disease affecting skin and muscles and seen primarily in the Collie and Shetland Sheepdog breeds. The cause is unknown. Severely affected dogs experience cyclic recurrences over their lifetime. Signs include extensive alopecia, crusting, inflammation on the face, hyper- or hypopigmentation, erosion, and ulceration of the skin. Scarring may or may not be apparent. Lesions of the skin and muscles vary in severity. Bony prominences, especially on the muzzle and around the eyes and ears are favored areas for the development of early lesions. The signs may develop as early as at 6 months of age; later, paws and tip of the tails may be affected, followed by inflammation of the paw pads.
Inflammation of the claw bed may lead to claw degeneration. Pain and itching may follow, if ulceration develops. Muscle involvement is usually subtle in nature and may be limited to atrophy of certain facial muscles, with subsequent difficulties in chewing and swallowing. Severely affected dogs show growth retardation, enlargement of the esophagus (resulting in chronic regurgitation), lameness, stiff gait, and muscle degeneration.
Infertility is an additional feature of severe dermatomyositis. In young dogs, signs of canine familial dermatomyositis are similar to those seen in demodicosis and dermatophytosis. Diagnosis is based on skin scraping (to rule out demodicosis) and fungal culture (to rule out dermatophytosis). Examination of the electrical activity of the muscles and associated nerves is used to confirm the diagnosis. Although corticosteroids have been used, the results are variable. Mildly affected young dogs may improve without any treatment. The prognosis is usually fair, although in some dogs, staphylococcal infections may develop. These dogs should be housed away from their littermates.
- Uc Davis Book of Dogs: The Complete Medical Reference Guide for Dogs and Puppies
- Emily J. Walder, Verena K. Affolter, Peter J. Ihrke, Thelma Lee Gross. Skin Diseases Of The Dog And Cat: Clinical and Histopathologic Diagnosis
- Larry M. Cornelius, Duncan C. Ferguson, Michael D. Lorenz. Small Animal Medical Therapeutics