The pathology of the spleen in steroid-treated immune thrombocytopenic purpura.

The spleen is a central organ in the pathophysiology of immune thrombocytopenic purpura (ITP). Splenic lymphoid tissue synthesizes anti-platelet IgG, and splenic cordal macrophages destroy platelets coated with anti-platelet antibodies. The morphologic features of the spleen in this disease reflect this splenic function: hypertrophied lymphoid follicles with secondary germinal centers in the white pulp, with perivascular plasma cells in the red pulp and evidence of increased platelet phagocytosis in cords of the Billroth. Foamy macrophages and evidence of a variable degree of extramedullary hematopoiesis also have been noted. The authors have studied 17 spleens removed for therapeutic purposes in patients with proven ITP previously treated with varying amounts of corticosteroids. In all cases there was little or no morphologic evidence of follicular hyperplasia or plasmacytosis. However, platelet sequestration and phagocytosis were demonstrated easily in all cases, both in histologic sections and in touch imprints. The authors' findings indicate that morphologic evidence of lymphoid activation characteristic in spleens from patients with ITP usually is ablated by prior corticosteroid therapy but that the characteristic platelet sequestration and phagocytosis persists.