(See also Overview of Tubulointerstitial Diseases.)
Tubulointerstitial disease and glomerular damage are the most common types of renal damage. Glomerular damage is usually the predominant mechanism. The mechanisms by which light chains damage nephrons directly are unknown. Hypercalcemia contributes to renal insufficiency by decreasing renal blood flow.
Types of tubulointerstitial renal disorders in multiple myeloma include
Light chains saturate the reabsorptive capacity of the proximal tubule, reach the distal nephron, and combine with filtered proteins and Tamm-Horsfall mucoprotein (secreted by cells of the thick ascending limb of Henle) to form obstructive casts. The term myeloma kidney or myeloma cast nephropathy generally refers to renal insufficiency caused by the tubulointerstitial damage that results. Factors that predispose to cast formation include the following:
Types of glomerular renal disorders in multiple myeloma include
AL amyloidosis results in glomerular deposition of AL amyloid in the mesangial, subepithelial, or subendothelial areas or a combination. Amyloid deposition is with randomly oriented, nonbranching fibrils composed of the variable regions of lambda light chains. Light chain deposition disease, which also can occur with lymphoma and macroglobulinemia, is glomerular deposition of nonpolymerized light chains (ie, without fibrils), generally the constant regions of kappa chains.
Rarely, a nonproliferative, noninflammatory glomerulopathy that causes nephrotic-range proteinuria can develop in advanced myeloma-related renal disease. A proliferative glomerulonephritis occasionally develops as an early form of light chain deposition disease with progression to membranoproliferative glomerulonephritis and nodular glomerulopathy reminiscent of diabetic nephropathy; nephrotic-range proteinuria is common.
Diagnosis of myeloma-related kidney disease is suggested by the following combination of findings:
The diagnosis should be suspected even in patients without a history of or findings suggesting multiple myeloma, particularly if total urinary protein is elevated out of proportion to urinary albumin. Total urinary protein is measured over 24 hours (and is often elevated enough to suggest nephrotic syndrome) or as a spot measurement (eg, using the urine sulfosalicylic acid test); urinary albumin is measured by dipstick.
Diagnosis of light chain tubulointerstitial disease (myeloma kidney) is confirmed by a markedly positive urine sulfosalicylic acid test suggesting significant nonalbumin proteins, by urine protein electrophoresis (UPEP), or both.
Diagnosis of glomerulopathy is confirmed by renal biopsy. Renal biopsy may demonstrate light chain deposition in 30 to 50% of patients with myeloma despite the absence of detectable serum or urine paraproteins by immunoelectrophoresis.
Kidney disease is a major predictor of overall prognosis in multiple myeloma. Prognosis is good for patients with tubulointerstitial and glomerular light chain deposition disease who receive treatment. Prognosis is worse for patients with AL amyloidosis, in whom amyloid deposition continues and progresses to renal failure in most cases. In either form without treatment, virtually all renal lesions progress to renal failure.
Management of multiple myeloma and prevention of volume depletion (eg, using normal saline for volume expansion) to maintain a high urine flow rate are the primary treatments. In addition, factors that worsen renal function (eg, hypercalcemia, hyperuricemia, use of nephrotoxic drugs) should be avoided or treated.
Several measures are often recommended but are of unproved efficacy. Plasma exchange may be tried to remove light chains. Alkalinization of the urine to help change the net charge of the light chain and reduce charge interaction with Tamm-Horsfall mucoprotein may make the light chains more soluble. Colchicine may be given to decrease secretion of Tamm-Horsfall mucoprotein into the lumen and to decrease the interaction with light chains, thus decreasing toxicity. Loop diuretics may be avoided to prevent volume depletion and high distal sodium concentrations that can worsen myeloma-related kidney disease.
Patients with multiple myeloma can sustain tubulointerstitial and glomerular damage by various mechanisms.
Suspect myeloma-related kidney disease if patients have unexplained renal insufficiency, bland urinary sediment, and/or increased nonalbumin urinary proteins.
Treat myeloma and maintain euvolemia.