P1 Intra-renal involvement in primary antiphospholipid antibodies syndrome: data from two Italian centers

Objective Apart from the distinct microvascular lesions characterizing antiphospholipid antibodies nephropathy (aPL-N), various glomerular conditions, especially membranous nephropathy (MN) and focal segmental glomerulosclerosis (FSGS), have been reported in primary APS (PAPS) patients, even without evidence of aPL-related vascular lesions. Our aims are i) to evaluate factors associated to intra-renal involvement in PAPS patients ii) to clinically and histologically characterize PAPS patients with non-aPL-N intra-renal involvement. Methods An observational retrospective multicentric study was conducted including all PAPS patients regularly and prospectively followed in the period 1984–2023 in the Centers. Case-control study: PAPS patients with intra-renal involvement histologically confirmed vs PAPS patients without signs of renal involvement (figure 1). Results Among the 258 PAPS patients evaluated (78% females, median age at onset: 32 years, 67% thrombotic phenotype, 54% obstetric phenotype, 41% triple aPL+), 7% had intra-renal involvement manifesting with isolated urinary abnormalities in 53% of the cases. At renal biopsy 35% had classic aPL-N injuries while 65% had non-aPL-N intra-renal lesions. i) As compared to patients without intra-renal involvement, the 17 patients with intra-renal involvement had less macrovascular thrombosis, more thrombocytopenia, epilepsy, and LA+ (table 1). ii) PAPS patients with non-aPL-N intra-renal lesions had MN in 55% and FSGS in 45% of the cases, with some degree of non-specific vascular injury (glomerular basement membrane wrinkling, mild hyaline plaques) in 64%. As compared to patients with aPL-N, they had more frequently normal serum creatinine and higher 24h-proteinuria levels (0.980.6–1.2 vs 1.91.2–2.0 mg/dL; p:0.095 and 3.51.9–3.9 vs 0.50.4–0.5 g/24h; p:0.003, respectively), but no differences in systemic autoantibodies or complement levels. All the patients belonging to this subgroup experienced aPL-related events (73% had thrombosis, 83% had obstetric events, 36% had 'extra-criteria' manifestations), that in 45% of the cases were preceded by the renal disease. Conclusions The present study highlights the importance of conducting appropriate renal assessment and, when necessary, renal biopsy in PAPS patients, even in presence of mild urinary alterations. On the other hand, from the nephrologists' point of view, it may be relevant to consider the routinary research of aPL at time of glomerulopathies evaluation, in particular because of the aPL prognostic role in the development of subsequent related events.