Prognostic value of kidney biopsy in myeloma cast nephropathy: a retrospective study of 70 patients

Background. Light chain myeloma cast nephropathy (MCN) is the major cause of renal failure in multiple myeloma and strongly impacts patient survival. The role of kidney biopsy in the management of MCN is unclear. Methods. Renal pathological findings were retrospectively studied in 70 patients with multiple myeloma and MCN. Patients were categorized according to the achievement or not of renal response, as defined by estimated glomerular filtration rate (eGFR) >= 30 mL/min/1.73 m(2) and/or dialysis independence at 3 months. Results. Thirty-two patients (46%) achieved a renal response. In the whole study population, the following parameters differed significantly between patients with and without renal response, respectively: baseline median eGFR (13.3 versus 9.3 mL/min/1.73 m(2), P = 0.017), Acute Kidney Injury Network Stage 3 (68.8 versus 92.1%, P = 0.019), haematological response rate (94 versus 34%, P < 0.0001), median percentage of free light chain (FLC) reduction at Day 21 (92 versus 24%, P = 0.006) and median number of casts/10 fields (14 versus 25, P = 0.005). The extent of interstitial fibrosis and tubular atrophy was similar. In multivariate analysis, only FLC reduction at Day 21 was significantly associated with renal response. However, when considering only the subgroup of haematological responders, both median number of casts [odds ratio (OR) = 0.93, 95% confidence interval (95% CI): 0.88-0.98, P = 0.01] and extent of tubular atrophy (OR = 0.03, 95% CI: 0.00-0.52, P = 0.02) were independent predictors of renal response. Conclusions. In MCN, the presence of numerous casts and diffuse tubular atrophy is associated with poor renal prognosis. These data suggest that additional strategies to reduce FLC burden should be considered in patients with extensive cast formation.