Indeterminate cell histiocytosis: a case report.

Indeterminate cell histiocytosis is a rare neoplasm composed of cells with mixed characteristics of Langerhans cells and non-Langerhans cells. An otherwise healthy, 36-year-old woman presented with asymptomatic generalized papules and nodules that had appeared on all four extremities, the trunk, and cheeks in the previous 6 months. The lesions were firm, painless, non-pruritic, and slightly flesh-yellow or reddish-brown in color. Histopathologic, immunohistochemical examination and electron microscopic studies showed characteristic findings of indeterminate cell histiocytosis: diffuse proliferative histiocytes infiltrating the dermis without epidermotropism or atypia; neoplastic cells expressing markers characteristic of both Langerhans cells (CD1a, S-100) and focal monocytes/macrophages (Factor XIIIa, CD68); and no Birbeck granules within the cytoplasm of the neoplastic cells. Flow cytometry revealed more CD34+ cells in the peripheral blood of the patient than in peripheral blood from a control. Interestingly, the patient responded favorably to psoralen ultraviolet A-range treatment. Herein, we present this case and review the literature.