Seronegative Anti-Glomerular Basement Membrane Disease Presenting as Rapidly Progressive Glomerulonephritis: A Diagnostic Challenge from South India

Anti-glomerular basement membrane (anti-GBM) disease is a rare, fulminant autoimmune small-vessel vasculitis characterized by rapidly progressive glomerulonephritis (RPGN), with or without pulmonary haemorrhage. Detection of circulating anti-GBM antibodies is traditionally considered central to diagnosis; however, seronegative variants pose a significant diagnostic challenge, particularly in regions where infection-related and ANCA-associated glomerulonephritides are more prevalent. We report the case of a 45-year-old male from South India who presented with subacute onset bilateral pedal edema, facial puffiness, and progressive exertional dyspnoea. Laboratory evaluation revealed nephrotic-range proteinuria, active urinary sediment, and rapidly worsening renal dysfunction. Extensive serological evaluation, including anti-GBM antibodies, antinuclear antibodies, and ANCA, was negative. Given the clinical suspicion of RPGN, renal biopsy was performed and demonstrated crescentic glomerulonephritis with linear IgG deposition along the glomerular basement membrane on immunofluorescence, establishing the diagnosis of anti-GBM disease.