Background Systemic Lupus Erythematosus (SLE) is a systemic autoimmune disease which affects multiple organ systems. One of the most severe complications is renal involvement, present in approximately 30-50% of SLE patients. 15-20% of SLE patients develop the anti-phospholipid syndrome, characterised by the occurrence of anti-phospholipid antibodies together with obstetric morbidity and/or thrombosis, and also renal thrombotic microangiopathy (TMA).

Objectives To examine the occurrence of vascular changes consistent with TMA in renal biopsies from SLE-patients, and to investigate if the occurrence of TMA was associated with other pathological findings in renal tissue, autoantibody specificities or clinical manifestations.

Methods Renal biopsies from 129 patients with SLE were investigated. The mean number of biopsies per patient was 2 (range 1-8), in all 274 renal biopsies were evaluated. Data including information from biopsy reports, serum creatinine (mmol/L), and clinical information concerning hypertension were collected. Autoantibodies against cardiolipin (aCL) and b₂glykoprotein1 (b₂GP1) were measured by enzyme-linked immunosorbent assay (ELISA) according to clinical routine used at the laboratory at the time of biopsy. We also recorded if patients had a positive lupus anticoagulant (LAC) test determined with a modified Dilute Russel Viper Venom method.

Results Thirty-one (24%) of the patients were male and 98 (76%) were female. A total of 221 biopsies (81%) were from female patients and 53 (19%) from male patients. The mean age at time of biopsy was 39 (15-85) years. We found a prevalence of TMA among SLE-patients with renal involvement of 14/129 (11%). Compared to patients with SLE glomerulonephritis (GN), occurrence of TMA was associated with intima changes in vessels (OR=18, CI:2.4-142.1, p<0.001), and with tubular atrophy (OR=6, CI:0.8-48.8, p<0.05). TMA was also associated with the presence of a positive LAC test (OR=10, CI:2.3-45.1, P<0.05) as well as with the presence of anti-b₂GP1 antibodies (OR=5, CI:1.2-21.1, p<0.05). However, there was no association with aCL-antibodies of either IgM or IgG-isotype.There was also a positive association between TMA and hypertension (OR=5, CI:1.6-13.8, p<0.01) and SLE-patients with TMA had significantly higher levels of creatinine as compared to SLE GN patients (mean 179 vs 104, p<0.001). There was no difference in gender and occurrence of TMA.

Conclusions TMA is a serious condition, which in this study occurred in 11% of SLE patients with renal involvement. Compared to patients with SLE GN, patients with TMA had more pronounced intima changes in the vessels, tubular atrophy and higher serum creatinine levels, thus at increased risk of developing impaired renal function. As TMA requires different treatment strategies compared to SLE GN, it is important to identify and treat TMA at an early stage in order to prevent renal damage.

Disclosure of Interest None Declared