Discrepant Biopsy and Serological Findings in Nephrotic Syndrome: A Case of Phospholipase A2 Receptor (PLA2R)-Positive Membranous Nephropathy Mimicking Post-infectious Glomerulonephritis

Anti-phospholipase A2 receptor (PLA2R) antibody testing has transformed the diagnosis of membranous nephropathy in adults with nephrotic syndrome. However, discrepancies between serological and histopathological findings can create significant diagnostic and therapeutic uncertainty. We report the case of a 72-year-old woman with heavy proteinuria, hypoalbuminaemia, and markedly elevated PLA2R antibodies, whose initial renal biopsy suggested a resolving post-infectious glomerulonephritis. Owing to persistent nephrotic syndrome, a second biopsy performed four weeks later revealed membranous nephropathy, prompting treatment with prednisolone and rituximab. Her course was complicated by steroid-refractory microscopic colitis, rapidly progressive vitiligo, severe fluid overload resistant to high-dose diuretics, and recurrent nocturnal desaturation, revealing previously undiagnosed chronic obstructive pulmonary disease. This case highlights the importance of repeat renal biopsy when serological and histological findings diverge and illustrates the challenges of delivering immunosuppression in patients with multiple comorbidities. Early multidisciplinary input was essential in establishing the diagnosis and planning treatment.