#6849 CLINICOPATHOLOGIC CHARACTERISTICS IN RENAL THROMBOTIC MICROANGIOPATHY

Abstract

Abstract Background and Aims Thrombotic microangiopathy (TMA) is a life-threatening condition that can be caused on the background of various mechanisms, converging to a severe endotheliopathy that often affects the kidneys. Morphologic features of TMA on kidney biopsy have not been systematically studied. We studied the diagnostic and prognostic role of a kidney biopsy in patients with TMA, either linked to a coexisting condition (i.e., secondary TMA) or not (i.e., complement-mediated [C-]TMA). Method Patients with TMA on kidney biopsy and an enzymatic activity of ADAMTS13 >10% were recruited from the Limburg Renal Registry. C-TMA was defined as massive ex vivo C5b9 formation on the endothelium and/or rare variants in complement genes [1]; secondary TMA was defined as the presence of a coexisting condition and normal complement regulation. Kidney tissue sections were studied for activity and chronicity; also, C3d staining was performed. Results C-TMA and secondary TMA was diagnosed in 35 and 39 patients, respectively. The diagnosis TMA was based on a kidney biopsy in 52 (70%) out of 74 patients as systemic hemolysis, that is, microangiopathic hemolytic anemia (MAHA) and thrombocytopenia, was lacking. Morphologic activity, such as, glomerular thrombosis and mesangiolysis, was not associated with MAHA (p = 0.116) and/or thrombocytopenia (p = 0.380). Morphologic activity, however, was associated with C-TMA, as was lower age and higher serum creatinine. C3d staining did not differentiate C-TMA from secondary TMA. A Mayo Clinic Chronicity Score (MCCS) of ≥4 was associated with an increased partial- (p = 0.023) and complete renal remission rate (p = 0.030), and decreased end-stage kidney disease (p = 0.050). Conclusions Only a small proportion of patients with TMA on kidney biopsy initially present with systemic hemolysis, suggesting an essential role of histologic examination to prevent underdiagnosing. Glomerular thrombosis and mesangiolysis were associated with C-TMA, however there is no role for staining of C3d in differentiating C-TMA from secondary TMA. An increased MCCS indicates worse renal outcome in patients with TMA.