Inconsistency between serum IgG κ and glomerular IgA λ chain types in proliferative glomerulonephritis with monoclonal deposits successfully treated with daratumumab-based therapy

RATIONALE: Here we report a rare case of a patient with serum immunoglobulin G (IgG) κ and glomerular immunoglobulin A (IgA) λ chain types in proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID). The patient showed clinical improvement after treatment with daratumumab combined with bortezomib and dexamethasone. To date, data on daratumumab use in patients with PGNMID are limited, and its treatment remains challenging. PATIENT CONCERNS: We report a rare case of a 50-year-old male patient with PGNMID in whom serum kappa free light chain (FLC) and lambda were significantly higher than average, and immunoglobulins were IgG-kappa and FLC-kappa types. The Bence Jones protein test was positive, and the urine immunofixation electrophoresis revealed a kappa light-chain type. DIAGNOSES: Renal biopsy was performed after admission. The pathological diagnosis was IgA λ-type PGNMID combined with acute tubulointerstitial injury and chronic disease. INTERVENTIONS: The patient became seriously ill upon admission and progressed rapidly. After administration of the first dose of daratumumab at 100 mg, 3 courses of bortezomib (1.3 mg/m2) were administered in combination with dexamethasone (10 mg) for 21 days. OUTCOMES: After 3 sessions of treatment, the patient's blood creatinine level was stable at 300 μmol/L, urine volume was normal, and serum kappa FLC was reduced to 477 mg/L. LESSONS: This rare case of PGNMID showed a discrepancy between serum IgG κ and glomerular IgA λ chain. Treatment with daratumumab, bortezomib, and dexamethasone significantly reduced serum FLC levels and stabilized the blood creatinine level. Daratumumab is a promising drug for the treatment of PGNMID.