Histiocytosis X. Flow cytometric DNA-content and immunohistochemical and ultrastructural analysis.

A 76-year-old man developed a generalized orange-red nodular eruption associated with constitutional symptoms. A biopsy specimen of a nodule revealed an extensive infiltration of histiocytes with relatively abundant cytoplasm and folded nuclei. Electron microscopy showed Langerhans' cell granules, which confirmed the diagnosis of histiocytosis X. Results of immunohistochemical studies revealed a pattern of antigen expression usually found in histiocytosis X, including Ia, T6, and S100. Analysis of the DNA content of the cells with flow cytometry revealed an aneuploid peak. The patient responded partially to topical mechlorethamine hydrochloride therapy.