Malignant histiocytosis presenting as multiple erythematous plaques and cutaneous depigmentation.

We report on a patient with malignant histiocytosis (MH) presenting as multiple erythematous plaques and cutaneous depigmentation on her neck and chest. In a biopsy of an erythematous plaque, atypical large, foamy histiocytes infiltrated the dermis and positively stained with antibodies to lysozyme, leukocyte common antigen, and KP-1 (CD68). A few similar atypical cells were present in the superficial dermis focally in the depigmented areas. With use of immunohistochemical studies, most cases previously diagnosed as MH have been reclassified as T-cell lymphoma, B-cell lymphoma, or Ki-1-positive anaplastic large cell lymphoma. However, a few cases of "true" MH characterized by authentic histiocytes have been reported, presenting usually as red nodules. To our knowledge, our patient is the first with MH to present with erythematous plaques and vitiligo-like depigmentation.