Langerhans-cell histiocytosis in an adult patient with multiple myeloma

A 44-year-old man who had suffered for 6 years from multiple myeloma developed multiple papules on the face and chest. Histological examination of these papules revealed the infiltration of predominantly histiocytic cells into the dermis and into parts of the epidermis. These cells were seen on electron-microscopic study to have Langerhans granules in the cytoplasm, which led to a diagnosis of Langerhans-cell histiocytosis concomitant with multiple myeloma. Possible explanations for this unusual association are discussed.