Examples include systemic lupus erythematosus, pemphigus erythematosus, and a variety of less well-defined immunologic diseases. Histologic and immunodiagnostic evaluation of the skin can be diagnostic. Dermatomyositis is a disease described in the Collie and Shetland sheepdog. Affected animals generally develop skin disease at 12-14 weeks of age. Lesions consist of papules, vesicles, pustules, crusts, erythema, and focal alopecia of the face, pinnae, tail and extremities over bony prominences.
Lesions are pruritic in some cases.
Myositis is the chief systemic abnormality. It is usually observed clinically as reduced temporal muscle mass, although in severely affected animals there may be generalized reduction of muscle mass. The myositis may involve esophageal muscle and megaesophagus has been reported as a sequela. Secondary skin infections may also be seen. The pathogenesis of this disorder appears to be immunologically-mediated, however the exact mechanism is unknown.