Thrombotic microangiopathy after kidney transplantation: causes, clinical specifics and outcomes

Background: Thrombotic microangiopathy (TMA) is a clinical and morphological phenomenon characterized by specific microvascular injury, microangiopathic hemolytic anemia, and damage of various target organs. TMA after kidney transplantation (post-renal transplant TMA) is a serious complication affecting the recipient and graft survival. Aim: To analyze the timing, causes, specifics of the clinical course and outcomes of TMA in renal transplant recipients. Materials and methods: This one-center study was based on a comprehensive examination and follow-up of 697 patients who had undergone 728 kidney transplantations (KT) from deceased donors in 2003–2019. Post-transplant TMA of the renal graft was confirmed morphologically in all cases. Results: We identified 32 episodes of post-transplant TMA in 32 patients; thus, the incidence of TMA was 4.4%. All cases developed after KT de novo ; no recurrent TMA was observed. TMA was systemic in 37.5% and locally renal in 62.5% of the patients. The median time to the development of post-transplant TMA was 0.55 (range, 0.1 to 51.6) months. The patients with TMA did not differ from those without by gender, age, body mass index, underlying disorders, type and duration of dialysis before KT, protocols of immunosuppressive therapy, incidence of surgical, urological, infectious, cardiovascular and oncological complications. The patients with TMA were significantly more likely to have graft rejection (25.0% vs 11.2%, p = 0.035) and a never-functioning transplant (28.1% vs 4.9%, p < 0.001). The presence of TMA negatively affected the transplantation outcomes. The cumulative 1-year graft survival in the patients without and with TMA was 91% and 44%, respectively, whereas their 5-year survival rates were 68% and 25% (p < 0.001). The leading causes of TMA were: donor pathology (31.2%), antibody-mediated rejection (28.1%), and cyclosporine/tacrolimus nephrotoxicity (21.9%); the proportion of other causes was 18.8%. A combination of TMA etiological factors was identified in 68.7% of the recipients. The recipients with of calcineurin inhibitors nephrotoxicity had a more favorable prognosis compared to those with other causes of TMA. Conclusion: Post-renal transplant TMA is an infrequent but serious complication that worsens the graft survival and often is life-threatening for recipients. In most cases, TMA develops in the early post-operative period; however, it can occur any time thereafter. To improve the outcome of TMA, early diag