Monoclonal Gammopathy in Amyotrophic Lateral Sclerosis: No Impact on Clinical Progression and Immunotherapy Outcomes

Abstract

Background: The association between amyotrophic lateral sclerosis (ALS) and monoclonal gammopathy has been proposed, but evidence on its prevalence, clinical relevance, and treatment response remains limited, especially in Asian populations. This study aimed to investigate the prevalence of monoclonal gammopathy in Korean patients with ALS and evaluate the impact of immunotherapy. Methods: This registry-based study analyzed Korean patients with ALS at a tertiary referral hospital (2005–2023). All patients underwent electrophoresis and immunofixation electrophoresis to detect monoclonal gammopathy. Clinical progression was assessed using ALSFRS-R scores, disease progression rate (ΔFS), survival analysis, and electrophysiological evaluations. Results: Among 2400 patients with ALS, monoclonal gammopathy was identified in 1.0% (25/2400). Prevalence increased with age, 1.9% in patients aged ≥ 65 years and 0.7% (13/1755) aged < 65 years. Patients with ALS and monoclonal gammopathy were older (63.2 vs. 57.1; p = 0.01) and predominantly male (7.3:1 vs. 1.5:1; p < 0.01). Immunotherapy targeting monoclonal gammopathy did not significantly affect disease progression (pre-treatment ΔFS 1.00 ± 1.23 vs. post-treatment ΔFS 0.94 ± 0.86; p = 0.46) or survival outcomes (median survival 55.0 vs. 57.0 months; log-rank p = 0.93). Nerve conduction study did not correlate with clinical outcomes. IgM monoclonal gammopathy demonstrated later slower disease progression (initial ΔFS, overall ΔFS; p < 0.05) compared to IgA and IgG subtypes. Conclusion: Monoclonal gammopathy in Korean patients with ALS was not more prevalent than in the general population, and immunotherapy did not impact ALS progression or survival. Clinical features may vary by immunoglobulin subtype. This collectively suggests minimal clinical significance of monoclonal gammopathy in ALS.