myeloma cast nephropathy; light chain cast nephropathy

Etiology

• always associated with multiple myeloma.

Epidemiology

• 20% of patients with multiple myeloma

Pathology

• Ig light chains in urine
• renal tubular injury
• obstructive uropathy of tubular origin
  • filtered light chains endocytosed by proximal tubule cells are nephrotoxic, resulting in proximal tubular dysfunction
• always associated with multiple myeloma

Clinical manifestations

• acute or slowly progressive kidney injury

Laboratory

• 24 hour urine protein
  • high levels of Ig light chains in urine
  • albumin in urine may be normal
  • nephrotic level proteinuria, but not nephrotic syndrome (no edeme
  • urine dipstick detects albumin, not Ig light chains
• serum protein electrophoresis
• high serum free light chains
• urine protein electrophoresis
• immunofixation electrophoresis
• hypercalcemia
• anemia

Radiology

• lytic bone lesions may be noted

Differential diagnosis

• AA amyloidodsis
  • frequently present with the nephrotic syndrome
  • history of an inflammatory disease, edema, hypoalbuminemia
• monoclonal gammopathy of renal significance
  • no hypercalcemia, anemia, or lytic bone lesions
• fibrillary glomerulopathy
  • hematuria, hypertension

Management

• treatment of multiple myeloma
  • reduce free Ig light chains with chemtherapy
• avoid bisphosphonates
  • pamidronate may induce acute renal failure & nephrotic syndrome
  • zoledronate may induce acute tubular necrosis
  • contraindicated if GFR > 30 mL/min
• avoid NSAIDs, especially in patients with volume depletion

More general terms

• multiple myeloma; plasmacytoma/plasma cell myeloma
• nephropathy