Dermatomyositis is an uncommon condition in dogs that predominantly affects the skin and, to a lesser extent, striated muscle.1 The exact cause is unknown, but an immune-mediated pathogenesis resulting in an ischemic dermatopathy is suspected.2 Dermatomyositis is predominantly seen in collies and Shetland sheepdogs, in which a familial predisposition is present. Other breeds may be affected, but a similar familial relationship has not been shown.
Clinical signs are variable in dogs and range from mild with spontaneous resolution to severe and debilitating. Cutaneous lesions usually appear before 6 months of age and occur on the face (periocular region, perioral region, muzzle), ears, distal extremities, and tail.2 Lesions are initially characterized by erythema, alopecia, scaling, and crusting and may progress to cicatricial alopecia. When clinical signs of myositis are present, they correlate to the severity of skin disease and manifest as difficulties with prehension of food, atrophy of masticatory and distal limb musculature, gait abnormalities, or regurgitation secondary to megaesophagus.3
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