Patchy hair loss including bacterial demodex, or ringworm infection, or hormonal diseases such as hypothyroidism and Cushing's disease. These diseases should be ruled out by appropriate testing. Skin biopsy of affected areas shows dysplastic (abnormally shaped) hair follicles which are filled with keratin.
In mildly affected animals, the only sign is the formation of asymptomatic comedones (blackheads) which are dilated hair follicles on the midline of the back. In more severely affected dogs, secondary bacterial infection may develop, causing crusts, pimples, hair loss and itching.
Lesions occur most commonly on the trunk, the legs, the digits (toe), the scrotum, the lips, the anus, and the nose. The lesions are typically ulcerated or cauliflower-like in appearance, bleed easily and are typically solitary.