Lambert-Eaton myasthenic syndrome in United States veterans with small cell lung carcinoma (SCLC).

e20148 Background: Lambert-Eaton Myasthenic Syndrome (LEMS) is a rare autoimmune disorder characterized by muscle weakness, fatigue, and autonomic dysfunction. 50-60% of LEMS cases present as paraneoplastic, mostly with SCLC. US Veterans have higher rates of SCLC incidence due to increased tobacco use and exposure to service-related carcinogens. The true prevalence, survival rate, and treatment of veterans with SCLC and LEMS remains uncertain, further research is necessary for improving clinical recognition of LEMS and to provide critical insights into the burden of this paraneoplastic condition in a high-risk population. Methods: Veterans with SCLC between October 1, 1999 and December 31, 2024 were retrospectively identified from the national Veterans Affairs (VA) Corporate Data Warehouse by ICD-O-3 codes. ICD-9 and ICD-10 codes for LEMS, Myasthenic Syndrome, or myoneural disorders were used to identify patients with a probable diagnosis of LEMS. The presence of LEMS was confirmed in patients via text matching in hematology, oncology, or neurology clinic notes. We used a binomial logistic regression to analyze the frequency of LEMS in SCLC patients over 5-year time periods. The overall survival of patients with SCLC compared to patients with SCLC and LEMS was analyzed using Cox proportional hazards ratio (HR) and Kaplan-Meier survival model. Results: We identified 25,953 distinct patients with SCLC for the period queried. Our screening method yielded TIU notes for 80 SCLC patients. We could confirm a diagnosis of LEMS in 71 cases, probable LEMS in 6 cases, and uncertain LEMS in 3 cases. The crude total count (confirmed plus probable cases) of LEMS was 2.97 per 1000 veterans with SCLC. Amifampridine (3,4-Diaminopyridine) was involved in the treatment for 7 of the 71 confirmed LEMS cases while 42 of these cases were treated with pyridostigmine. There was not a significant correlation between LEMS diagnosis and the 5-year time period frequency rate. The Cox HR for SCLC-LEMS to SCLC was 0.72 (95% CI: 0.55-0.93). Overall survival of patients in SCLC was significantly higher for the group with LEMS (p-value = 0.011). Conclusions: Among US veterans with SCLC, LEMS is a rare disorder consistently observed over the past 25 years with a slight negative, non-significant incidence trend. The majority of LEMS patients were treated with pyridostigmine rather than amifampridine. SCLC patients with LEMS exhibited improved survival compared to those with SCLC alone. LEMS 5-year time period frequency. Dates Number of SCLC Patients Number of confirmed LEMS cases (Percentage) 1999 - 2005 6397 21 (0.33%) 2006 - 2010 5563 19 (0.34%) 2011 - 2015 5583 13 (0.23%) 2016 - 2020 4980 14 (0.28%) 2021 - 2024 3435 4 (0.12%) Total 25953 71 (0.27%)