ITP is caused by an anti-platelet IgG produced largely by the spleen. Aggregates of foamy histiocytes are seen in the red pulp. The foamy appearance is secondary to accumulation of phospholipids from phagocytized platelets. Additional histologic findings in ITP in spleen include formation of secondary lymphoid follicles, dilatation of sinuses, and mild myeloid metaplasia.
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