Patient with a leg ulcer caused by pyoderma gangrenosum, a rare skin condition. The cause of pyoderma gangrenosum is not fully understood but it may result from an overactive immune system. It affects people of all ages, but is particularly seen in patients over 50. The ulcers are painful and can spread if left untreated. Treatment typically involves steroids, removal of dead tissue and antibiotics. Treatment is usually successful in stopping the spread of ulcers but healing can take months or years, and skin grafts may be necessary.