A Challenging Case of IgG4-Related Kidney Disease Accompanied With Positive Serologic Tests of Lupus Erythematosus.

The case report presents a male patient in his mid-60s with a history of hypertension, benign prostatic hyperplasia and chronic kidney disease (CKD). He presented with gradually increasing serum creatinine levels and hyperglobulinemia, leading to suspicion of multiple myeloma. However, subsequent testing revealed features consistent with systemic lupus erythematosus (SLE) and IgG4-related kidney disease (IgG4-RKD). The patient's laboratory results included anaemia, positive ANA and anti-dsDNA and elevated serum IgG4 levels. A kidney biopsy showed extensive interstitial fibrosis, plasma cell infiltration and a high number of IgG4-positive plasma cells, suggesting the diagnosis of IgG4-RKD overlapping with SLE. Treatment involved prednisolone, mycophenolate mofetil for IgG4-RKD and hydroxychloroquine for SLE. The patient's case highlights the challenges in diagnosing overlapping IgG4-RKD and SLE. The current criteria for diagnosing these diseases may be complicated by atypical presentations, leading to potential diagnostic confusion. This report underscores the importance of histopathological confirmation and comprehensive diagnostic criteria to differentiate between overlapping autoimmune conditions. Immunosuppressive therapy remains the cornerstone for managing both IgG4-related disease and SLE, with treatment tailored based on disease severity and organ involvement. The patient's response to treatment and follow-up monitoring are crucial for assessing outcomes and adjusting management to minimise disease relapse and therapy-related complications.