Allopurinol hypersensitivity. Granular deposition of IgM at the dermal-epidermal junction

A patient with allopurinol hypersensitivity, manifested by fever, lymphadenopathy and a severe erythematous, morbilliform, maculopapular rash was studied. On immunofluorescent staining of the patient's skin, heavy granular deposits of immunoglobulin M (IgM) were found at the dermal-epidermal junction. Transformation of the patient's lymphocytes could not be effected by a variety of combinations of allopurinol, allopurinol metabolites and serum. These data suggested that the hypersensitivity reaction caused by allopurinol had immune complex deposition as the central feature in pathogenesis. The predominance of IgM may provide a distinctive feature from the deposits generally seen in systemic and discoid lupus erythematosus.