This disorder typically affects patients over 60 years of age, but it can rarely occur in children. There is no racial or ethnic predilection and the incidence is equal in males and females.
Clinically, bullous pemphigoid (BP) is characterized by large tense bullae that are often preceded by red, urticarial patches or plaques. Lesions are most commonly located on the lower abdomen, inner thighs, and flexor forearms although they may occur anywhere. Mucous membrane involvement is uncommon. Lesions are usually associated with marked pruritus but they do not scar.
BP is an acquired autoimmune disorder that occurs secondary to the formation of antibodies that interact with bullous pemphigoid antigen 1 (230 kDa intrahemidesmosomal antigen) and bullous pemphigoid antigen 2 (180 kDa hemidesmosomal transmembrane antigen, also known as type XVII collagen). This interaction is then followed by an inflammatory response leading to dermal-epidermal separation. On electron microscopic exam, blister formation occurs in the lamina lucida, between the basal cell membrane and the lamina densa. On histopathologic exam, lesions show a subepidermal blister with fluid, fibrin, and inflammatory cells including numerous eosinophils. Direct IF of perilesional skin demonstrates linear C3 and IgG. Indirect IF using normal stratified squamous epithelia (such as human epidermis or monkey esophagus) is positive in 70% to 80% of patients. However, in contrast to patients with pemphigus, these titers do not correlate well with disease extent or activity. In salt incubated skin, the BP antigen localizes to the roof of the split (i.e. the bottom of the basal cells). This technique enables differentiation from EBA where the antibodies bind to the base of the blister (dermal side of the split).
BP is often a self-limited disease with a fairly good prognosis. Many treated patients will go into remission over a 5 to 6 year period. However the disease may persist for 10 years or more.