Splenic pathology in thrombotic thrombocytopenic purpura.

To determine splenic pathology in thrombotic thrombocytopenic purpura (TTP), 10 spleens and two accessory spleens were studied. The eight women and two men ranged from 20 to 66 years of age (mean age, 39 years). Three spleens were enlarged. Thrombi were noted in arteries and arterioles in nine specimens: no associated inflammation was seen. Periodic acid-Schiff-positive diastase-resistant hyaline subendothelial deposits (SEDs) were present in all cases. Some arterioles showed a transition between thrombi and SEDs. The presence of platelets or platelet-related material in SEDs and thrombi was documented by factor VIII staining. Hyperplasia of B cells and germinal centers was present in 67%, and periarteriolar concentric fibrosis ("onion-skinning") in 58%. Histiocytes showed prominent iron deposits in 92% and hemophagocytosis in 83% of cases. Extramedullary hematopoiesis was present in 42%. Blood lakes, infarcts, and endothelial hyperplasia were rarely noted; microaneurysms were not seen. Ten spleens from patients with idiopathic thrombocytopenic purpura and 10 age-matched control spleens rarely showed SEDs or hemosiderosis and did not show hemophagocytosis or thrombi. We conclude that subendothelial deposits may be related to platelet thrombi incorporated into vessel walls. Germinal centers and periarteriolar concentric fibrosis may indicate an immunologic role in TTP, as in systemic lupus erythematosus.