Thrombotic Microangiopathy involving the kidney: A Histopathologic Perspective

Hippokratia 2003, 7(4):152-158

H Liapiss


The aim of the study was to evaluate the relative frequency of Thrombotic microangiopathy (TMA) and to identify histopathologic variables that may facilitate timely and specific therapy. The frequency of TMA among medical and transplant renal biopsies in this institution was < 1%. Eighty percent of TMA occurred in adults, slightly more in women than men. The most frequent cause of TMA in medical kidney biopsies of adults was lupus nephritis followed by cryoglobulenemic glomerulonephritis secondary to hepatitis C and immunosuppressive drugs such as bleomycin and mitomycin. In the traansplant biopsies, the most frequent cause of TMA was cyclosporine A (CsA) toxicity. In children, 50% (4/8) occurred in transplants, and was also due to CsA toxicity; the remaining cases were either classic HUS/TTP or atypical forms of TMA. Notably, clinically evident hemolysis was present in a minority of the cases (8/41). Histopathologically, lupus associated TMA had characteristic immune complex deposits. CsA and other immunosuppressive drugs associated with TMA had fibrinoid necrosis or mesangiolysis. Classic HUS had arteriolar mucoid intimal proliferation, while onion skinning was a characteristic feature of malignant hypertension and connective tissue disorders affecting the kidney. Finally, two cases of atypical childhood HUS with microthrombi on renal biopsy were associated with idiopathic peripheral eosinophilia. Electron microscipy was important in assessing the full spectrum of pathologic changes of TMA that implicate endothelial cell damage. The study demonstrates that the diagnosis of TMA is often made by renal biopsy. Hemolysis is not infrequently absent. Pathologic findings span a spectrum of manifestations, not just thrombosis. Skillful evaluation and standardization of renal biopsy analysis with immunofluorescence and electron microscopy are essential for diagnosis.