A rare inflammatory disease of unknown etiology that usually occurs in elderly patients with lighter skin phototypes. There is a slight male predominance. Clinically characterized by sterile pustules and chronic crusted erosions. Crusts resolve leaving atrophy and scarring alopecia, and new areas of pustulation develop within a few days. Two types are described: scalp and legs. Clinical appearance, histology, and response to therapy are the same in both sites, but scalp lesions develop in areas of long-standing sun damage, whereas leg lesions occur on non-sun-damaged skin of patients with chronic venous stasis. The disease has a chronic, recurring, and slow but progressive course. It may lead to cutaneous malignancies in the scar tissue.