Crystalline appearance in light chain cast nephropathy is associated with higher early mortality in patients with newly diagnosed multiple myeloma.

Background: Light chain cast nephropathy (LCCN) is the most common kidney lesion in multiple myeloma patients. LCCN may exhibit a crystalline appearance. The frequency and clinical significance of crystalline LCCN are not well understood. Here, we report the first retrospective study of crystalline LCCN.

Methods: Twenty-six patients with LCCN were enrolled. We studied the clinicopathological features and outcomes of LCCN patients and compared ordinary LCCN patients (n = 18) with crystalline LCCN patients (n = 8).

Results: Crystalline LCCN was not rare (8/26, 30.8%) in our study. The median age of LCCN patients was 57.5 (range, 41-75) years. No patients presented with nephrotic syndrome. No significant differences in clinical features were observed between the two groups. All crystalline LCCN patients suffered from advanced multiple myeloma and acute kidney injury. There was a dominance of the λ isotype (7/8, 87.5%) in patients with crystalline LCCN. Patients with ordinary LCCN had significantly higher scores of tubular atrophy and acute tubular injury than those with crystalline LCCN. The crystalline casts of 5 crystalline LCCN patients stained negative with antihuman Tamm-Horsfall glycoprotein. There were no significant differences in the median overall survival between the crystalline LCCN group and the ordinary LCCN group (6.0 months vs. 35.0 months, p = 0.173). However, crystalline LCCN patients had higher early mortality than ordinary LCCN patients (50.0% vs 11.1%, p = 0.03).

Conclusion: Crystalline LCCN patients had higher early mortality than ordinary LCCN patients. Thus, for patients with LCCN, crystalline appearance should be screened carefully.