BACKGROUND: Whether IgA nephropathy (IgAN) in patients with systemic lupus erythematosus (SLE) represents a coincidental comorbidity or a distinct clinico-pathological entity remains unclear. This study aimed to characterise the demographic, clinical, pathological, and prognostic features of this rare association. METHODS: We conducted a systematic review of the PubMed and Embase databases to 31 May 2025 were conducted to identify all reported cases of biopsy-proven IgAN in patients with SLE, excluding cases with concomitant thrombotic microangiopathy, negative Gd-IgA1 immunostaining, prior IgA vasculitis, or ANA-negative disease. Study quality was assessed using the JBI checklist. Individual patient data were pooled; descriptive statistics summarized clinical features, and group comparisons were performed using Mann-Whitney U and Fisher's exact tests. Individual patient data were extracted and analyzed as a single cohort. Renal outcomes were defined as either a ≥ 40% decline in estimated glomerular filtration rate (eGFR) from baseline or progression to end-stage renal disease. RESULTS: Thirty-one patients (25.8% male; mean age 40.8 ± 15.8 years; 67.7% Asian) were included. Median proteinuria was 1.10 g/24 h, and 12.9% presented with nephrotic syndrome. Microscopic haematuria was observed in 93.5% of patients. Mean eGFR at biopsy was 84.0 ± 53.4 mL/min/1.73 m², with 12.9% exhibiting acute kidney injury (AKI). All patients were antinuclear antibody-positive, 64.5% were anti-dsDNA-positive, and 55.2% had hypocomplementaemia. Renal biopsy revealed dominant mesangial IgA and complement C3 deposition, with electron-dense deposits confined to the mesangium in all but one case. Immunosuppression (glucocorticoids 87.1%; cyclophosphamide 22.6%) yielded complete remission in 54.8% of patients. Over a median follow-up of 16.5 months, 27.8% of patients reached the renal endpoint, including three of four patients with AKI. CONCLUSIONS: Limited by retrospective case report methodology, this largest cohort to date suggests IgAN complicating SLE manifests a distinctive phenotype that bridges features of primary IgAN and lupus nephritis. Although immunosuppression is effective, long-term renal risk remains non-negligible. Early recognition and targeted therapy may improve outcomes. CLINICAL TRIAL NUMBER: Not applicable.
Zhao et al. (Fri,) studied this question.