The term “lipid” is generic and includes all fats and substances compounded with fats. Disturbances of lipid metabolism are responsible for a number of clinical entities for which the term “lipidoses” has been proposed. Clinical interest is centered chiefly in xanthomatoses, xanthomatous tissue changes, Gaucher’s disease, Nimeann-Pick disease, Tay-Sachs disease, lipochondrodystrophy.
The common characteristic of these clinical disturbances is an accumulation of large, poorly staining, lipid-containing cells (histiocytes) which arise primarily from reticuloendothelial cells in all parts of the body. Most of these diseases appear sufficiently different clinically, chemically and pathologically to be defined as clinical entities.
However, occasional instances of organic
involvement with cells containing poorly classifiable lipid material do occur. The specific lipid in most of the aforementioned diseases has been chemically identified and serves as one of the criteria for diagnosis and classification. Cholesterol and its esters accumulate in xanthomatous cells, cerebroside (kerasin) in Gaucher’s disease and sphingomyelin in Niemann-Pick disease. In all instances a particular lipid predominates, but other lipids are also present abnormally in cells of patients with such disturbances.Three mechanism could be responsible for the lipidoses: (a) excessive production of a normal lipid and
saturation of the tissues involved in its removal; (b) normal rate of production of an essentially normal lipid, but with an abnormality of the end organ tissues resulting in local accumulation (Unzman’s Gaucher lipoprotein hypothesis); (c) production of an abnormal lipid.In Gaucher’s and Niemann-Pick disease the lipid changes in the cells are well developed when clinical symptoms first become manifest. In the Hand-Schüller-Christian syndrome, on the other hand, the earliest lesion is a granuloma, and cholesterolization and xanthoma cell formation occur only with progression of the disease, if at all. Thus in this disease the intracellular lipid disturbance appears to be a secondary and not a primary manifestation, and for this reason the disease has been included in the reticuloendothelioses. Secondary xanthomatous tissue changes occur in other conditions when the reticular and histiocytic cells have an excessive amount of lipid material made available to them systemically as in hyperlipemic states, or locally as in chronic inflammatory reactions and neoplastic growth.