Percentage of urinary albumin excretion and serum-free light-chain reduction are important determinants of renal response in myeloma patients with moderate to severe renal impairment

Reversal of renal dysfunction significantly affects the prognosis of multiple myeloma (MM) with renal impairment (RI). There is no reliable test for predicting reversibility of RI in MM patients. We postulated that MM with high albuminuria may reflect glomerular disease that is difficult to reverse. Here, we examined the impact of urinary albumin excretion. We retrospectively analyzed 279 patients admitted to our hospital from April 2000 to December 2013. Clinical variables and laboratory data that may affect myeloma treatment response were extracted. The results were examined for relationship to renal response by univariate and multivariate analysis. RI (estimated glomerular filtration rate ≦50 ml/min per 1.73 m²) was observed in 116 patients (46%) and renal responses of renal complete response, renal partial response, renal minor response and no response were obtained in 46 (40%), 15 (13%), 13 (11%) and 42 (36%) patients, respectively. Although renal recovery was significantly associated with Durie–Salmon 1 or 2 (P=0.02), myeloma response better than very good partial response (P=0.03), involved free light-chain (iFLC) reduction from baseline 80% at day 12 (P=0.005), ≧95% at day 21 (P<0.001) and urinary albumin ≦25% on admission (P<0.001) on univariate analysis, only reduction of iFLC 95% at day 21 (P=0.015) and urinary albumin ≦25% (P=0.007) remained significant for any renal response. Our observation indicates that increased urinary albumin excretion >25% and reduction of iFLC ≦95% on day 21 were associated with favorable renal recovery in MM patients with RI, and were considered as negative predictors for renal response.Renal impairment (RI) is a major cause of morbidity and mortality in patients with multiple myeloma (MM) and approximately 50 and 20% of patients have RI and acute renal failure depending of its definition.^{1, 2, 3, 4} The presence of RI limits the use of antimyeloma agents and eligibility for stem cell transplantation, and, therefore, places these patients at higher risk for disease progression and myeloma-related complications. RI is also associated with an increased risk of early death,^5,6 although the recent introduction of effective novel agents, such as thalidomide, bortezomib and lenalidomide, has led to the improved survival even in patients with RI.^7,8The most common cause of RI in MM is cast nephropathy, which may be seen in up to 30% of patients;⁹ other causes of RI include monoclonal immunoglobulin (Ig) deposition disease and amyloidosis. It should be noted that non-paraprotein-associated renal lesions are also seen in 25% of patients. As most patients with MM are elderly, age-related comorbidities such as hypertension and diabetes may also be associated with the decline of renal function.As the reversibility of renal function may be dependent on the pathogenesis of renal disease,¹⁰ correct renal pathology is necessary for successful treatment. Use of bortezomib-based regimens in combination with or without plasma exchange has been reported to yield high rates of renal recovery in patients with cast nephropathy.^{11, 12, 13, 14} However, reversibility of renal function in cases other than cast nephropathy is largely unknown. Kidney biopsy cannot be performed in all patients with MM and RI because of its various limitations and possible complications. Recently, Nasr et al.⁹ reported the clinicopathologic correlations in MM patients with kidney biopsy; they reported the highest levels of albuminuria in patients with amyloidosis and lowest levels in those with cast nephropathy.Despite the heterogeneity of renal pathology, urine albuminuria is thought to reflect glomerular injury, and patients with cast nephropathy usually show tubulointerstitial injury and lack heavy albuminuria. Therefore, we postulated that renal response may be different according to urinary albumin excretion. In this study, we retrospectively analyzed the clinical variables that may affect renal response in 116 MM patients with RI at our hospital. We also examined the predictive capacity of urinary albumin and serum-free light-chain (FLC) reduction on renal recovery of RI patients with MM.