Pemphigoid nodularis.

A 61-year-old man with prurigo nodularis subsequently developed bullous pemphigoid. Direct immunofluorescence studies of a prurigo nodularis-like lesion and peribullous skin showed the deposition of IgG, IgA, and C3 in a linear pattern at the basement membrane zone. Indirect immunofluorescence studies disclosed circulating anti-basement membrane zone antibodies. Immunoelectron microscopy revealed IgG, IgA, and C3 distributed in the lamina lucida and on the undersurface of the basal keratinocytes in both peribullous and prurigo nodularis lesions. These findings confirmed the diagnosis of pemphigoid nodularis.