High-grade follicular B-cell lymphoma-associated C3 rapidly progressive glomerulonephritis: a rare association.

Rapidly progressive glomerulonephritis (GN) in the context of B-cell lymphoma is rare, with most cases involving diffuse-large B-cell lymphoma or marginal zone lymphoma. Kidney biopsies are infrequently performed in this population, further limiting diagnostic clarity. Here, we report a case of newly diagnosed follicular large B-cell lymphoma (FLBCL) presenting with a nephritic syndrome, characterised by haematuria, hypertension and heavy proteinuria, caused by C3 crescentic GN, requiring dialysis. The patient was treated with polatuzumab, bendamustine and rituximab, which was well tolerated. Renal function gradually improved, leading to dialysis discontinuation, coinciding with lymphoma remission. This case underscores the atypical presentation of FLBCL, including renal dysfunction as an early manifestation, and the importance of prompt diagnosis and targeted therapy.