Myeloma kidney

Light chain casts surrounded by inflammatory cells in myeloma cast nephropathy

Stompor et al. reviewed renal involvement in multiple myeloma (MM). Renal abnormalities can be seen in 25-75% of patients with MM. The overall prognosis in these patients were poorer than those without renal lesions. Early detection and treatment of MM can improve long term renal outcome.

There are a number of factors determining the type and severity of renal involvement in MM: the amount and type of abnormal light chains (LCs), urine pH, calicinuria, amount of Tamm-Horsfall (TH) protein in distal nephron. The common renal diseases in MM are:

1. Myeloma cast nephropathy is most common form of renal involvement in MM and associated with poor renal and patient outcome. The interaction between the naturally-occurring Tamm-Horsfall protein and abnormal kappa LC is the basis of LC cast formation. Hypercalciuria and natriuresis enhance this process.
2. Amyloidosis of AL type is found in 15-35% of MM patients undergoing renal biopsy. Proteinuria is the leading renal abnormality. Lambda LC is found to be the precursor of amyloid protein in majority of the cases. Some of lambda LC amyloid cannot be identified by immunostaining due to change in immunologic fragments. Patients with AL amyloidosis have poor prognosis especially ones with extrarenal amyloid deposition.
3. Light chain deposition disease (LCDD) is found in 20-25% of MM patients undergoing renal biopsy. Abnormal light chain, mainly kappa, deposits in subendothelial space and mesangium causing proteinuria and extracellular matrix accumulation. Glomerular lesion is similar to diabetic nodular glomerulosclerosis.

Other rare form of renal diseases include proximal tubule disorder resembling Fanconi syndrome. These diseases can occur concurrently. Renal biopsy is advocated in most if not all patients with MM.