Hexagonal crystals in the bone marrow in patients with myeloproliferative disease and preleukaemia

In epoxy resin-embedded bone marrow biopsies from 238 cases of myeloproliferative disease and preleukaemia, crystalline inclusions were found in the bone marrow cells of 24 (10.1%), most often in patients with acute myeloproliferative disease (23%). By light microscopy the crystals were easily recognized after Giemsa staining, lying within the cytoplasm of bone marrow macrophages. By electron microscopy the hexagonal crystals were encountered chiefly within secondary lysosomes of the macrophages, but also within immature myeloid cells in one of the two cases studied. In the latter a tight-fitting membrane around the crystals suggested that they were of lysosomal origin and represented a form of abnormal granulation. We suggest that the presence of crystals in myeloid cells represents a kind of abnormal granula formation in the neoplastic cells. In the macrophages the crystals lodge in secondary lysosomes, probably after phagocytosis of crystal-bearing non-viable myeloid cells. The accumulation of crystals in lysosomes indicates resistance to degradation.