Indeterminate cell histiocytosis (ICH) is a rare disorder, characterized by infiltration of the skin by neoplastic cells that are characteristically positive for S-100 and CD1a, but lack Birbeck's granules. A 75-year-old man presented with a 4-year history of multiple papules on the trunk, limbs, face and neck. Skin biopsy revealed dense infiltration of histiocytic cells that were CD1a+/S100+, but lacked Birbeck's granules. No other abnormality was seen during a general examination including a computed tomography scan of the body, gallium scintigraphy, and an abdominal sonography. Broadband ultraviolet B (UVB) treatment was used for the skin lesions, and partial but almost complete remission was obtained. The case suggests that UVB phototherapy is an option for treatment of ICH.
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