De novo thrombotic microangiopathy. An underrated complication of renal transplantation.

After kidney transplantation thrombotic microangiopathy (TMA) may recur in patients with previous hemolytic uremic syndrome or may develop de novo. De novo TMA has been reported to occur in less than 1% of renal transplant recipients by large registries, but single center series reported an incidence of the disease as high as 14-20%. A number of factors may predispose to posttransplant TMA, including ischemia-reperfusion injury, acute rejection, viral infection. Immunosuppressive treatment can also contribute to the development of de novo TMA. Calcineurin inhibitors may cause or aggravate endothelial lesions through their pronecrotic, vasoactive and profibrotic activity. Anti-mTOR agents may delay the repair of the endothelial damage through their interference with endothelial growth factor. Usually, TMA develops in the early posttransplant period but may also occur later. Clinically, TMA is characterized by progressive renal failure and hypertension. Microangiopathic hemolytic anemia and thrombocytopenia may occur in about 60% of cases. Histologically, TMA may be localized to glomeruli or may involve arteries or both. The prognosis depends on the timely diagnosis and on histological picture. Treatment is based on the removal of inciting factors. Early plasmapheresis could improve clinical signs and symptoms and rescue renal function in a number of patients. Anecdotal successes have also been reported with intravenous immunoglobulins and rituximab.