Delayed but Durable Remission to Rituximab in PLA2R-Associated Membranous Nephropathy Despite B-Cell Reconstitution: A Case Report

Rituximab (RTX) is widely used as first-line therapy for PLA2R-associated membranous nephropathy (MN), but the optimal timing for assessing response and guiding retreatment remains uncertain, particularly in patients with slow clinical improvement. We report a 46-year-old man with PLA ₂ R-associated MN who showed poor response to high-dose glucocorticoids and was subsequently treated with a low-dose, fractionated RTX regimen (total 3.6 g over 14 months).Notably, a significant reduction in proteinuria was not observed until 19 months after treatment initiation, when partial remission (proteinuria < 3.5 g/day) was first achieved. During 44 months of follow-up, proteinuria continued to decline and remission was maintained, while anti-PLA ₂ R antibodies remained negative despite gradual reconstitution of circulating CD19⁺ B cells, and no further immunosuppressive therapy was administered.This case demonstrates a markedly delayed but durable clinical response to rituximab and illustrates that B-cell repopulation does not necessarily indicate disease relapse when anti-PLA ₂ R antibodies remain suppressed, supporting the value of antibody-guided rather than B-cell-guided monitoring in slow responders.