Clinical-Pathological Characteristics of Renal Injuries Identify Different Clusters in Patients With Antiphospholipid Antibodies

Introduction: Significant heterogeneity still exists in the nomenclature of renal involvement in antiphospholipid syndrome (APS). Methods: We applied a hierarchical cluster analysis to determine subgroups of patients according to clinical, laboratory, and renal histology characteristics in a cohort of subjects with confirmed antiphospholipid antibodies (aPL) positivity and biopsy proven aPL-related renal injuries. Kidney outcomes were then assessed at 12 months. Results: A total of 123 aPL-positive patients were included in the study (101 [82%] female, 109 [88.6%] with systemic lupus erythematosus [SLE], 14 (11.4%) with primary APS [PAPS]). Three clusters were identified. Twenty-three patients (18.7%) were included in the first cluster (cluster 1), characterized by a higher prevalence of glomerular capillary and arteriolar thrombi and fragmented red blood cells in the subendothelial space. Cluster 2 included 33 patients (26.8%) and showed a higher prevalence of fibromyointimal proliferative lesions as seen in hyperplastic vasculopathy. Cluster 3 was the largest (67 patients, mainly with SLE) and was characterized by higher prevalence of subendothelial edema, of both glomerular capillaries and arterioles. Conclusion: Three different clusters of patients with aPL and renal injuries emerged from our study as follows: the first, with the worst renal prognosis, was associated with features of thrombotic microangiopathy (TMA), thrombosis, triple aPL positivity and higher adjusted Global APS Score (aGAPSS) values; the second, characterized by hyperplastic vasculopathy with an intermediate prognosis, was seen more frequently in patients with cerebrovascular manifestations; and the third, more benign in terms of outcomes and with no overt association with thrombotic features, was characterized by endothelial swelling in concomitant lupus nephritis (LN).