Rare case report: A man with rheumatoid arthritis developed membranous nephropathy and ANCA- associated vasculitis successively

Abstract Background Renal involvement in rheumatoid arthritis (RA) is relatively common, which may be due to the RA itself or may be associated with the use of nephrotoxic drugs. The widespread use of biological agents has ledto an increasing number of reports of RA-related nephropathy. Case presentation We report a rare case of sequential membranous nephropathy (MN) and ANCA-associated vasculitis (AAV) in a 74-year-old male with seropositive rheumatoid arthritis (RF 389 IU/mL, anti-CCP 360 U/mL). One month after initiating etanercept (25 mgtwice weekly), he developed nephrotic syndrome (proteinuria 5.42 g/day, albumin 19.9 g/L) and elevated anti-PLA2R (33.78 RU/mL). Renal biopsy revealed stage I MN with granular IgG/C3 deposits. Despite rituximab therapy (cumulative 1600 mg) improving proteinuria to 1.81 g/day, the patient presented with acute kidney injury (SCr 1016 μmol/L), hematuria, and positive MPO-ANCA (169.8 RU/mL)six months later, which wasconsistent with AAV. Immunosuppression with methylprednisolone and cyclophosphamide reduced the SCr level to 583 μmol/L, although dialysis dependence persisted. Conclusion To our knowledge, this represents the first documented case of sequential MN and AAV in an RA patient who received etanercept and rituximab therapy during the clinical course. While direct causality remains unproven, this case underscores the need for vigilance regarding complex renal complications in RA patients managed with biologics, irrespective of etiological determinants.