Niemann-Pick disease: lipid storage in bone marrow macrophages.

A histochemical study of lipids in bone marrow smears was performed in a series of 15 cases of Niemann-Pick disease (NPD). It revealed significant differences in the amount of lipids stored in macrophages of sphingomyelinase (SMase) deficiency (types A, B) and type C. Early deposition of uniform, anisotropic droplets of sphingomyelin (Maltese-cross birefringence) in lysosomes was a feature of a 9-member group of SMase deficiency (types A, B). The type C group (six cases) was characterized by a remarkable difference in the degree of phospholipid, mainly sphingomyelin, deposition. The total amount of phospholipids was small on average, and very often inversely proportional to pronounced structural storage changes. This indirect relationship was most prominent in the early phase of the disease and grew less prominent as the disease progressed further. The stored lipid was primarily isotropic. In longer lasting cases of both categories (SMase deficiency and type C) a considerable part of the storage cell population displayed ceroid deposition giving the appearance of a 'sea-blue histiocyte' independent of the type of NPD, but with definite predominance in SMase deficiency. The diagnostic value of the findings is discussed, and some pathogenetic conclusions suggested, particularly as regards type C. Lipid histochemistry of bone marrow smears is highly recommended as it represents a simple but highly efficient approach, capable of yielding valuable diagnostic information.