Characteristic mononuclear cells with distorted nuclei and abundant pale-staining cytoplasms together with osteoclast-like giant cells are the cytologic hallmarks of histiocytosis X. The demonstration of acid phosphatase within giant cells in paraffin-embedded sections is a valuable aid to diagnosis. The histologic differential diagnosis of histiocytosis X includes some allergic granulomas, Hodgkin's disease, myelomonocytic leukemia, mastocytosis, and malignant histiocytosis. Some technical prerequisites for accurate diagnosis of histiocytosis X are considered briefly.
Lichtenstein(1) first proposed the term histiocytosis X and stressed the morphologic identity of the atypical mononuclear cells in eosinophilic granuloma, Hand-Schuller-Christian's syndrome, and Abt-Letterer-Siwe's disease. Each of these conditions may affect the skin and produce lesions there which are diagnostic when viewed by conventional microscopy.
Although the histopathologic features of histiocytosis X have been described many times, the experience of any individual with it is usually limited, because the disease is so rare. I will give a crisp description of the histologic changes of histiocytosis X and emphasize an additional aid to diagnosis, namely, the finding in paraffin-embedded sections of acid phosphatase in some mononuclear cells and in large multinucleated cells of histiocytosis X.