Evolution of idiopathic membranous nephropathy to class v lupus nephritis: a case report and literature review

Background: The M-type phospholipase A2 receptor (PLA2R) antibody positivity is considered a specific serological marker for idiopathic membranous nephropathy (IMN), and its presence in class V lupus nephritis (LN) is rare. There is limited reporting on the longitudinal progression from IMN to systemic lupus erythematosus (SLE) with class V LN, particularly in cases with persistently positive anti-PLA2R antibodies. Case presentation: A 54-year-old woman presented with nephrotic syndrome in 2016, with initial renal biopsy showing podocyte disease. In 2020, disease recurrence with positive serum anti-PLA2R antibodies led to a second biopsy diagnosing IMN stage II. In 2024, she presented with edema and facial erythema. Serology revealed new-onset positive ANA and anti-dsDNA antibodies alongside persistent anti-PLA2R positivity, meeting SLE criteria. A third renal biopsy confirmed class V LN. After treatment with methylprednisolone and hydroxychloroquine, and following a rituximab infusion reaction, she achieved clinical remission with obinutuzumab. Conclusion: This case highlights that positive anti-PLA2R antibodies do not definitively exclude secondary MN such as class V LN. Long-term serological monitoring and repeat renal biopsy should be considered in IMN patients with atypical clinical evolution to identify potential transformation to LN.