Subtle clues to diagnosis by histochemistry. Histiocytosis X.

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.