Diffuse histiocytosis of the spleen and idiopathic thrombocytopenic purpura (ITP): histochemical and ultrastructural studies.

A case of ITP where the spleen was infiltrated diffusely and extensively by foamy macrophages is described. Among these macrophages were also clusters of cells with the morphologic and tinctorial characteristics of ceroid or "sea-blue" histiocytes. The ultrastructural characteristics of the foamy and ceroid histiocytes are described. Transition of ceroid cells into foamy macrophages is demonstrated, and intermediate forms were observed. It is postulated that the ceroid or sea-blue histiocytes are macrophages that contain platelets at an early stage of digestion, and when the phagocytosis of these platelets is completed, the macrophages become foamy. Therefore, it is suggested that the foamy cells and ceroid or sea-blue histiocytes seen in the spleen in cases of ITP are macrophages that have ingested and metabolized the abnormal platelets.