A Rare Case of Concurrent IgA Nephropathy and Anti-glomerular Basement Membrane (GBM) Disease

Introduction: Anti-glomerular basement membrane (anti-GBM) disease is a rare disorder, characterized by rapidly progressive glomerulonephritis (RPGN) with or without pulmonary involvement. Here, we report a patient presenting with RPGN due to anti-GBM disease, who was found to have mesangial IgA staining on immunofluorescence (IF), suggesting concurrent IgA nephropathy (IgAN). Case Description: A 38-year-old male with no known past medical history, presented with several days of abdominal pain, nausea, and vomiting. He was found to have acute kidney injury with initial serum creatinine of 7.9 mg/dL requiring hemodialysis. Initial workup included a urinalysis with +4 protein; innumerable RBCs and 5-10 WBCs per HPF; a urine protein-to-creatinine ratio of 3.10 g/g; and an unremarkable kidney ultrasound. Serologic workup was notable for an IgG anti-GBM titer of 2.5 units/mL (reference < 0.9), and anti-nuclear antibody (ANA) titer of 1:320. Other serological studies including MPO, PR3, C3, C4, hepatitis B and C, and PLA2R were normal or negative. Kidney biopsy light microscopy showed 25 glomeruli (20 with cellular and/or fibrous crescents, and 1 with mesangial expansion and hypercellularity). There was moderate interstitial scarring. IF showed linear staining of glomerular basement membrane for IgG (1+) and lambda/kappa (2+) consistent with anti-GBM glomerulonephritis. Additionally, mesangial regions were positive for IgA (1-2+), IgM (1+) and C3 (1+), consistent with IgA nephropathy. Patient received pulse dose glucocorticoids, oral and intravenous cyclophosphamide, and 10 sessions of plasmapheresis. He remained on kidney replacement therapy after induction treatment with an anti-GBM titer of 0.2 units/mL. Discussion: Concurrent IgAN with anti-GBM disease has been described sporadically in the literature with heterogeneous findings. These findings include linear IgA staining of GBM, concurrent mesangial IgA and linear IgG staining, and linear IgG staining with circulating IgA anti-GBM antibodies. The moderate scarring, mesangial involvement, and variable stages of crescent formation suggest that our patient may have had ongoing undiagnosed IgAN that preceded development of anti-GBM disease. Unlike other similar reported cases, he unfortunately did not have kidney function recovery.