Dermatomyositis is a hereditary condition that can cause skin lesions and, in severe cases, affect the muscles. D.M. primarily affects Shetland Sheepdogs and Collies, although dogs in other breeds have been diagnosed. Not every dog of these breeds shows signs of the disease but passes it to their offspring. There are various symptoms. Skin lesions may appear on the front legs, head, and ears. There may be extensive hair loss and scarring on the face and ears, as well as on the legs and the tip of the tail. The only way to diagnose D.M. is through a skin punch biopsy evaluated by a derma pathologist. There’s no test yet for dermatomyositis, which is thought to be one gene with variable expression, meaning that a dog can carry it without showing signs.