Daratumumab-Based Regimen Significantly Induced Remission of Crystalline Light Chain Proximal Tubulopathy: A Case Report

BACKGROUND Light chain proximal tubulopathy (LCPT) is a rare monoclonal immunoglobulin light chain-associated kidney disease. A few clinical case reports have shown that lenalidomide is an effective treatment for LCPT. Daratumumab, an anti-CD38 monoclonal antibody, has demonstrated efficacy in multiple myeloma and light chain amyloidosis, with good hematologic and organ response. However, the role of daratumumab in non-amyloid monoclonal gammopathy of renal significance requires further validation. CASE REPORT This report describes a case of LCPT that was unresponsive to lenalidomide but responded favorably to a daratumumab-based regimen. A middle-aged man presented with fatigue, nocturia, and hypokalemia as initial symptoms upon admission. Auxiliary examinations indicated renal dysfunction, without proteinuria. During the evaluation of secondary causes of renal dysfunction, serum immunofixation electrophoresis detected an IgA-Kappa-type M proteinemia, prompting a bone marrow aspiration for definitive diagnosis, which revealed 3% immature plasma cells. Finally, LCPT was diagnosed based on renal biopsy. After the diagnosis of the disease, early treatment with lenalidomide was not effective. However, after 5 cycles of treatment with daratumumab and dexamethasone, and a subsequent 2 cycles of daratumumab, bortezomib, cyclophosphamide, and dexamethasone (Dara-CyborD), the patient's clinical symptoms were completely relieved, blood potassium levels normalized, serum creatinine levels decreased 50%, and hematological remission was completely achieved. CONCLUSIONS Early diagnosis of LCPT, a rare monoclonal immunoglobulin disorder, has become increasingly feasible with advances in histopathological evaluation and hematological testing. This report shows that a daratumumab-based regimen or Dara-CyborD can offer a novel therapeutic strategy for the treatment of LCPT.