Remission of light chain proximal tubulopathy in IgG λ-type multiple myeloma by lenalidomide and dexamethasone therapy

Light chain proximal tubulopathy is a rare manifestation of monoclonal gammopathy. A 73-year-old Japanese woman was noted to have urinary protein and hypertension on health examination and visited the regional clinic. She was noted to have IgG lambda M protein and suspected of multiple myeloma. She was referred to us with massive proteinuria (7.5g/g creatinine) and Bence Jones proteinuria without renal dysfunction. A renal biopsy revealed no glomerular abnormalities, but a tubular cast was observed partially in tubules without tubular atrophy or a crystalline structure. Direct Fast Scarlet staining was absent both in glomerulus and vascular wall. Immunofluorescence revealed lambda light chain (LC) staining in the proximal tubules. Electron microscopy revealed nonspecific findings including increased lysosomes with irregular contours and mottled appearance. A bone marrow biopsy revealed plasma cell proliferation (35%) and multiple myeloma immunoglobulin G lambda type. She showed progressive anemia and decrease of eGFR with elevated level of urinary beta-2 microglobulin. She was treated with lenalidomide+dexamethasone (Ld). With Ld therapy, she achieved hematologic and nephrologic remission reducing the free LC, lambda/kappa ratio, urinary protein level, and urinary beta-2 microglobulin level.