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.