Background/Purpose: Thrombotic microangiopathy (TMA) is characterized by microvascular occlusion, systemic or intrarenal platelet aggregation and mechanical injury to erythrocytes.  It is a pathological endpoint that results from a disruption of the normal platelet–endothelial interface. TMA is one of the renal vascular lesions which can be found in systemic lupus erythematosus (SLE). The prevalence of renal TMA in SLE varies broadly between studies (8.1-24.3%), and there has been controversy regarding its prognostic value, as well as its association with antiphospholipid (APL) antibodies. The aim of this study was to evaluate risk factors and clinical outcomes for renal TMA in SLE patients. 

Methods: A retrospective, single-center study was performed. Renal biopsies from 245 SLE patients between 2008 and January 2014 were studied. We included patients with renal TMA, as well as controls adjusted by glomerulonephritis class, glomerular filtration rate (GFR), activity and chronicity indexes, and follow-up time. The variables that were measured included: autoantibody profile; hypertension, disease activity, SLEDAI, C3 and C4 levels, leukocyte and lymphocyte count, treatment and GFR at the time of the biopsy; GFR, SLEDAI and treatment during follow-up. Differences between groups were analyzed by Student t test or Mann-Whitney U test. Association between variables was assessed by OR (95% CI). Multivariate analysis was performed by binary logistic regression model.

Results: Twenty-three patients with renal TMA and 21 controls were included. TMA prevalence was 9.38%. 90.9% of subjects were female; mean age was 26.04 years in the TMA group and 27.9 years in controls. Mean follow-up was 25.56±14.39 months. At the time of the biopsy, GFR (ml/min/1.73m²) was 33.6±8.33 in the TMA group and 37.91±7.5 in controls; 56% of patients in the first group and 42.8% in the second required dialysis at that time. Two patients in the TMA group were diagnosed with thrombotic thrombocytopenic purpura (TTP); none of the others had clinical features suggestive of systemic TMA. Lymphopenia, platelet count, higher mean arterial pressure (MAP) and anti-Ro/SSA antibodies were associated with TMA. There was no association with APL syndrome or antibody positivity. There were no differences in SLEDAI score, GFR, end-stage renal disease (ESRD) or mortality between both groups throughout the follow-up period. At the end of follow-up, ESRD rates were 43.4% in the TMA group, and 42.8% in controls. After multivariate analysis, variables that remained significantly associated with renal TMA were: lymphopenia < 1000 cells/uL (OR 10.75, 95% CI 1.34-85.86, p=0.025), anti-Ro/SSA antibodies (OR 9.007, 1.49-54.11 95% CI, p=0.016), and MAP (OR 0.97, 95% CI 0.959-0.994, p=0.009). 

Conclusion: Lymphopenia and anti-Ro/SSA positivity were independent risk factors for renal TMA in SLE patients. This association could be related to their potential role in endothelial dysfunction and damage. Outcomes were similar for patients with the same GFR and biopsy characteristics, regardless of the presence of TMA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/renal-thrombotic-microangiopathy-in-systemic-lupus-erythematosus-novel-risk-factors-and-clinical-outcomes/