Multiple myeloma presenting as a novel mucocutaneous eruption.

A 71-year-old woman presented with exquisitely tender mucosal erosions, a diffuse polymorphous eruption, and night sweats. Workup revealed multiple myeloma with a monoclonal IgG-kappa paraprotein in the serum. Her severe oral involvement was suggestive of paraneoplastic pemphigus, but direct and indirect immunofluorescence tests were negative. A skin biopsy showed spongiosis and a sparse perivascular lymphocytic infiltrate, with occasional CD8-positive lymphocytes in the epidermis. Her lesions improved with intravenous immune globulin. Immunohistochemical staining on the formalin-fixed biopsy specimen was strongly positive for IgG and IgG-kappa in an epidermal "chicken-wire" pattern, but negative for IgG-lambda. Her pulmonary tissue stained negative for IgG-kappa, suggesting clinical relevance of the myeloma paraprotein in her epidermis. To our knowledge, this is the first report of a multiple myeloma patient with such an eruption.