[The 508th case: recurrent edema of bilateral lower extremities with proteinuria]

A 31-year-old man sought medical evaluation for a 2-year history of edema and proteinuria, with prior pathology suggesting atypical membranous nephropathy (MN). Despite treatment with a combination of steroids, calcineurin inhibitors, and four courses of rituximab (1 g, intravenous injection), the patient's nephrotic syndrome showed no relief (24 h urine protein peaked at 31.18 g/d), indicating refractory nephrotic syndrome. Later in the disease course, a sudden surge of creatinine level (322.5 μmol/L) prompted a renal biopsy, which revealed concurrent acute interstitial nephritis. Further treatment involving steroids, cyclophosphamide, and a fifth rituximab infusion (1 g, intravenous injection) resulted in improvement in renal function (serum creatinine: 322.5➝147 μmol/L), but the MN failed to achieve partial relief. Subsequent treatment with the novel humanized CD20 monoclonal antibody obinutuzumab (1 g, intravenous injection) was initiated. In the latest follow-up, anti-phospholipase-A2-receptor antibody (PLA2R) antibody were negative, B cells were eliminated, serum albumin was 36 g/L, urine protein-to-creatinine ratio was 4 810 mg/g, and serum creatinine was 162 μmol/L. This case underscores the potential efficacy of obinutuzumab in refractory MN. For advanced MN cases, prompt identification of the cause of acute kidney injury is crucial, emphasizing the need for targeted interventions to potentially stall renal function decline.