Renal Disease in Multiple Myeloma

Today we talked about a woman with acute kidney injury in the setting of multiple myeloma. Renal impairment is seen in 20-40% of newly diagnosed patients with myeloma.

There are many ways that MM can damage a kidney:

1) Pre-renal:
- Hypercalcemia via renal vasoconstriction and volume depletion

2) Renal Glomerular:
- Amyloid deposits in glomerulus
- Light Chain Deposition Disease (LCDD)
- rarely Type 1 cryoglobulinemia

3) Renal Tubulo-Interstitial
- Tubular Cast (aggregates of light chains and Tamm-Horsfall protein) formation- "Myeloma Kidney"
- Light chain toxicity to renal tubules
- Acquired Fanconi syndrome (also a form of light chain toxicity to the proximal tubule)- usually asymptomatic but detected because of hypouricemia
- Interstitial plasma cell infiltration
- Chronic urate nephropathy

One key question is whether or not a multiple myeloma patient with renal failure requires a kidney biopsy. If light chains are high in the urine, myeloma kidney is the likely cause. In a setting where 24-hour urine collection shows nephrotic syndrome but little to no light chains, a biopsy is useful to make the definitive diagnosis of amyloid or light-chain related glomerular disease.

Tubular cast on path: