Pityriasis lichenoides et varioliformis acuta immunohistopathologic study.

Immunoglobulin M and complement (Clq, C3 and C9) were found to be deposited together in the walls of affected blood vessels and also in the basement membrane zone of skin lesions from two patients with pityriasis lichenoides et varioliformis acuta (PLVA). The fluorescence appeared to be most intensely distributed in blood vessels which were affected by inflammatory infiltrates and frequently showed hyaline or fibrinoid changes of their walls. Deposits of C3 activator, fibrin and albumin were not observed. These findings suggest that the disease process in PLVA is the result of a vasculitis mediated by an immune complex and possibly by activation of the classical complement pathway. In addition, serum IgM was slightly increased in both patients.