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Abstract: PO1921

Light Chain Proximal Tubulopathy Without Fanconi Syndrome as the Sole Presenting Feature of Multiple Myeloma

Session Information

Category: Onco-Nephrology

  • 1500 Onco-Nephrology

Authors

  • Hodge, Joscelyn Eva, Madigan Army Medical Center, Tacoma, Washington, United States
  • Nicosia, Roberto F., University of Washington, Seattle, Washington, United States
  • Khayat, Maurice I., Madigan Army Medical Center, Tacoma, Washington, United States
Introduction

Light chain proximal tubulopathy (LCPT) is a rare pattern of immunoglobulin-related renal injury that occurs in the setting of dysproteinemias. Classic disease associations for LCPT are multiple myeloma, monoclonal gammopathy of renal significance, and other hematolymphoid neoplasms. The key LCPT pathologic feature is the accumulation of monoclonal light chains within the cytoplasm of proximal tubule (PT) cells with resultant clinical PT defects, proteinuria, and renal dysfunction.

Case Description

A 64-year-old male with prostatic adenocarcinoma presented for evaluation of incidentally discovered proteinuria (3.852 g/g creatinine) and stage two chronic kidney disease. Initial evaluation was significant for a kappa/lambda ratio of 474.79, serum M-spike of 0.9 g/dL, and urine M-spike of 1.082 g/dL. Urine immunofixation electrophoresis revealed 94.1% Bence-Jones protein (1.629 g/24h) comprising monoclonal IgG, kappa type. Other laboratory features of myeloma (hypercalcemia, anemia) were absent. Renal biopsy revealed monoclonal kappa light chain crystal inclusions in the cytoplasm of PT epithelial cells. Glomeruli show no significant histologic or ultrastructural abnormalities. Despite the severe histopathologic dysfunction, no clinical features of Fanconi Syndrome were present, including a negative work up for renal tubular acidosis as well as no renal wasting of phosphorous, amino acids, glucose, uric acid, or potassium. PET scan revealed diffuse marrow infiltrating disease with multiple lytic osseous lesions, and the patient was referred to oncology to begin chemotherapy.

Discussion

LCPT continues to be a rare pattern of kidney injury with significant variability in presentation based largely on the composition of the light chains. The toxicity of kappa light chains results from their ability to form crystals, which resist lysosomal proteolysis. Although our patient had extensive crystalline inclusions and significant evidence of tubular injury, no clinical evidence of proximal tubulopathy was evident with proteinuria as the sole presenting feature of diffuse myeloma.

The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army/Navy/Air Force, Department of Defense (DoD), or the U.S. Government.