Histiocytosis X of the skin in an elderly man.

A diffuse truncal cutaneous eruption of six months' duration in a 76-year-old man is described. Light and electron microscopy revealed infiltration of the papillary dermis and overlying epidermis by histiocytic cells containing Langerhans granules, findings characteristic of histiocytosis X. The Langerhans cell as a probable cell of origin and unifying feature for the subtypes of histiocytosis X is discussed. It is suggested that with increased awareness of the variability of histiocytosis X, atypical presentations will be identified more frequently.