Immunohistochemical and ultrastructural study of histiocytosis X and non-X histiocytoses.

The diagnostic reliability of ultrastructural and immunohistochemical examinations on routinely processed biopsy specimens of cutaneous histiocytic proliferations (histiocytosis X, n = 7; juvenile xanthogranuloma, n = 4; necrobiotic xanthogranuloma, n = 2; traumatic granuloma of the tongue, n = 1) was evaluated. S-100 protein, peanut agglutinin, and the antibody Mac-387 were used as markers for histiocytes. The frequency of Birbeck granule-containing cells in seven histiocytosis X lesions did not correspond with the number of S-100+ or peanut agglutinin+ cells. All neoplastic histiocytosis X cells were positive for S-100 protein and peanut agglutinin but were negative for Mac-387. Histiocytes of juvenile xanthogranuloma, necrobiotic xanthogranuloma, and traumatic granuloma were strongly positive for Mac-387 but were negative for S-100 protein and peanut agglutinin, except for the peanut agglutinin-reactive Touton giant cells. Mac-387 reliably differentiates histiocytic proliferations of the monocyte/macrophage system from those of the dendritic cell system. For the diagnosis of histiocytosis X, both S-100 protein and peanut agglutinin positivity in histiocytes is as reliable as ultrastructural demonstration of Birbeck granules.