This refers to one type of renal disease caused by multiple myeloma (MM). MM is a surprisingly common disease, occurring especially in older people, and making up about 10% of hematological malignancies. As you know (or will now learn), MM is a “plasma cell dyscrasia” that results in overproduction of light chains.
According to this excellent summary from JASN, about 50% of MM patients have renal insufficiency at time of diagnosis. The types of kidney injury that can occur range from:
- cast nephropathy (common)
- light-chain proteinuria (virtually all have proteinuria)
- nephrotic syndrome (10-20%)
- amyloidosis (5%)
- Fanconi syndrome (very rare)
“Myeloma kidney” refers specifically to cast nephropathy. Interestingly, up to 50% of patients initially have their kidney damage attributed to some other cause such as dehydration, infection, hypercalcemia, NSAID injury.
The light chains in MM are usually mutants that can’t be broken down or absorbed the same way that normal light chains are. They form casts in the renal tubules, and because they are “brittle” they can break off and rupture, causing interstitial nephritis. Light chains can also cause direct tubular necrosis, or in rare cases, form “needles” that injure the renal tubules.
Cast nephropathy is pretty serious business. The median survival for someone with cast nephropathy is 36 months, and renal failure is the second-highest cause of death (infection is first).
To treat MM cast nephropathy, it is best to treat the underlying MM with chemotherapy and aggressively manage the creatinine. But, 65% of patients with cast nephropathy will develop end-stage renal disease within 3 months of diagnosis. What to do then?
Another option is dialysis. In some studies, 40% of MM patients with cast nephropathy end up on dialysis and start anywhere from 3 months to a year after diagnosis. However, the effectiveness of dialysis depends on whether the person is responding to chemotherapy, the severity of their kidney disease, and other co-morbidities. Survival can be anywhere from 6 months to 3 years with dialysis, but MM patients still have a 2.5 relative risk of dying compared to other dialysis patients (and remember, these other patients are vasculopaths, severe diabetics, people on the verge of needing a kidney transplant).