Chronic organizing microangiopathy in a renal transplant recipient.

Thrombotic microangiopathy (TMA), not an uncommon but potentially serious complication of transplantation, occurs in 3–15% of renal transplant recipients [1,2]. De novo post-transplant TMA is mostly due to calcineurin inhibitor toxicity. Histologically, TMA is characterized by glomerular endocapillary damage with subendothelial accumulation of amorphous material. Narrowing or occlusion of capillaries with intravascular fibrin thrombi and fragmented erythrocytes is common. Similar changes may involve arterioles and arteries. Post-transplant TMA can be isolated to the allograft or can present with clinical and laboratory evidence of systemic TMA, including fever, haemolytic anaemia and renal failure. Intravascular haemolysis leads to the presence of schistocytes on peripheral blood smear, increased lactate dehydrogenase (LDH), and decreased haptoglobin levels in the systemic form of post-transplant TMA, which is often referred to as haemolytic–uraemic syndrome (HUS). Both localized and systemic TMA can present with acute renal failure, and both have been associated with decreased graft survival [1,2]. Here we use the descriptive term TMA to refer to both localized and systemic forms of post-transplant TMA, as well as to systemic forms of TMA in the general population, including HUS and thrombotic thrombocytopenic purpura (TTP). Recurrence of TMA following clinical resolution has been described in renal transplant recipients with pre-transplant TMA and in patients rechallenged with calcineurin inhibitors following an episode of calcineurin inhibitor-induced TMA [3]. The role of the initial endothelial insult in recurrent disease is unclear, and the significance of residual histological changes is not well described. Because the organizing phase of TMA may resemble chronic transplant glomerulopathy, it is unclear how often post-transplant TMA evolves into the fibrotic organizing phase. We present serial renal biopsies from a patient with acute humoral rejection and later development of malignant hypertension and systemic TMA, in whom intervening biopsies revealed fibrotic microvascular changes attributed to chronic organizing microangiopathy.