Background and design: As xanthoma disseminatum and histiocytosis X share clinicopathologic features, difficulties in diagnosis can arise. The use of immunocytochemical markers for S100 protein, factor XIIIa, lysozyme, alpha 1-antitrypsin, for adherence of peanut agglutinin and of antibodies LN3 (HLA-DR), Leu-M1 (CD15), QBEnd/10 (CD34), MAC 387, and KP1 (CD68) as an aid to conventional histology has been studied in routinely fixed skin biopsy specimens from seven patients with xanthoma disseminatum and 12 patients with histiocytosis X.
Results: Typically xanthoma disseminatum occurs in discrete foci below an intact epidermis with individual cells set within a delicate fibrillary connective tissue stroma. In contrast, histiocytosis X usually occurs as a diffuse lichenoid infiltrate that can extend to deeper tissues. Epidermal invasion is common and the cells tend to lie free separated by edema fluid. Characteristic histiocytosis X cells are ovoid with an indented or kidney-shaped nucleus that occupies half or more of the cell. Xanthoma disseminatum cells differ in showing irregular scalloped borders, a more extensive cytoplasm, and an ovoid vesicular nucleus. Most xanthoma disseminatum cells labeled strongly for factor XIIIa and with KP1; a few cells labeled only weakly with peanut agglutinin. In contrast, most histiocytosis X cells labeled for S100 protein and with LN3 and peanut agglutinin. All the other markers remained negative in both conditions and were thus noncontributory for differentiating xanthoma disseminatum from histiocytosis X.
Conclusions: We conclude that the differences in labeling patterns are a useful aid to histologic diagnosis of histiocytosis X and xanthoma disseminatum and they also reflect their separate histiogenesis.