Association of kappa light chain restriction with peripheral neuropathy among patients with non-IgM monoclonal gammopathy of undetermined significance.

Abstract

e20040 Background: Monoclonal gammopathy of undetermined significance (MGUS) can be associated with significant neurologic morbidity. Of non-IgM MGUS, types IgG and IgA are most commonly associated with peripheral neuropathy (PN). Methods: With IRB approval, we conducted a retrospective cohort study of consecutive patients with non-IgM type MGUS treated at our institution from 2014-2021. Other conditions potentially causing PN were excluded. Statistical analysis: Descriptive statistics were calculated to characterize the study population, and Relative Risk (RR) of PN was evaluated for selected patient, and disease, related factors. P < 0.05 was defined as statistically significant. Results: During the study period, 94 patients with non-IgM type MGUS were seen and comprised the study population. Twenty-two (23.4%) had evidence of PN. Median age was 74; 82% (18/22 ) were Caucasian; 73% (16/22) were women. 82% (18/22) patients had MGUS type IgG kappa or IgA kappa. We identified only 2 patients with each MGUS kappa light chain (LC) and MGUS IgG lambda. Median M-protein size was 0.11 g/dL, and median free LC value was 6.84 mg/L. Incidence/severity of kidney disease was similar in non-IgM MGUS patients with and without PN (p > 0.05). RR of PN was not found to be significantly different based on race or gender, although there appeared to be a tendency for women to be at higher risk compared to men (RR = 1.98, 95% CI = 0.85 to 4.60, p = 0.114.) Kappa LC restriction was strongly associated with PN (RR = 4.31, 95% CI = 1.58 to 11.78; p = 0.004). Electromyographic (EMG) studies identified 14 patients (64%) with distal symmetric axonal neuropathy (DSAN) and 8 patients (36%) with chronic inflammatory demyelinating polyneuropathy (CIDP). Clinically severe PN was identified in 11 (50%) patients; all were subsequently treated with IVIg therapy. Only 5/11 (45%) patients responded to IVIg, and the responses were only partial and transient. Conclusions: This is the first report, to our knowledge, of a significant association of kappa (as opposed to lambda) LC restriction with PN among patients with non-IgM type MGUS. Further investigation is warranted to explain this finding, elucidate pathophysiology and aid in developing more effective therapeutic options. Pending mechanistic characterization of this association, trials of contemporary agents used to treat other plasma cell disorders may be in order. Final statistical analysis, comparison to published series and significance will be presented.