Light chain crystalline podocytopathy

A 48-year-old white man with a history of smoldering myeloma diagnosed 2 years prior had worsening proteinuria from 1.5 g/d at myeloma diagnosis to 5.4 g/d. Serum creatinine was 1.3 mg/dl, up from 1.1 mg/dl 2 years prior. Hematologic evaluation revealed serum monoclonal Ig, IgGκ (1.1–1.4 g/dl), urine-free κ monoclonal Ig, an elevated serum-free κ/λ ratio of 26 (up from 10 at myeloma diagnosis), and 20% bone marrow κ-restricted plasmacytosis with standard-risk cytogenetics. He did not have anemia, hypercalcemia, bony lytic lesions, hypertension, vision problems, rash, or hematuria. Serum albumin was 3.8 g/dl. He had negative antinuclear antibody, antineutrophil cytoplasmic antibody, and hepatitis B and C serologies with normal complements. There was 1+ lower extremity edema.