A case of glomerulonephritis with dominant C3 with organized deposits complicated by non-tuberculous mycobacteria

We report a case of membranoproliferative glomerulonephritis (MPGN) with dominant C3 and uniquely organized deposits complicated by pulmonary non-tuberculous mycobacterial (NTM) infection. A 64-year-old man developed persistent urinary abnormalities following treatment with Mycobacterium malmoense . A renal biopsy revealed MPGN with characteristic fibrous organized deposits and strong complement C3c and fibrinogen positivity, but IgG, IgA, IgM, and C1q negativity. Immunosuppressive therapy was not administered. The patient’s renal function gradually declined, but subsequently stabilized with prolonged antibiotic therapy. This case highlights the importance of considering infection-related glomerulonephritis with C3-dominant organized deposits, particularly in the absence of any immunoglobulin involvement, as well as the need to distinguish this entity from primary C3 glomerulopathy.