To evaluate the potential for missed diagnoses of Lambert-Eaton myasthenic syndrome (LEMS) and autonomic dysfunction among patients with myasthenia gravis (MG) in the United States (US). 

MG and LEMS are both characterized by muscle weakness, but autonomic dysfunction is more common with LEMS. LEMS patients may initially be diagnosed as MG. Autonomic dysfunction in patients diagnosed with MG may indicate a missed LEMS diagnosis. Delayed diagnosis of LEMS, an underrecognized syndrome, can worsen morbidity, including delayed recognition of associated small cell lung cancer (SCLC).

Healthcare claims from a large US de-identified dataset (Symphony Health's PatientSource®, 3/1/2014-6/30/2023) were used. Eligible patients had ≥2 claims ≥30 days apart for MG and/or LEMS. In patients with MG, subsequent diagnoses of LEMS, lung cancer, and the receipt of SCLC therapies (etoposide + platinum-based chemotherapy) were ascertained according to the presence of autonomic disorder claims.

Among 130,762 eligible patients with MG, 400 (0.3%) also had LEMS diagnoses. Claims related to autonomic dysfunction were observed in 5.0% (n=6,562) of patients with MG. LEMS diagnoses were more frequent in patients with MG and autonomic dysfunction (0.8%) than in patients with MG without autonomic dysfunction (0.3%). Among 6,508 patients with MG and autonomic dysfunction, without a LEMS diagnosis, 138 patients were diagnosed with non-thymoma lung cancer. Of those who received SCLC therapies (n=4/138), none had LEMS codes in their claims history. In a subset of patients with MG diagnoses 1/1/2022 or later, VGCC antibody testing claims were infrequent but more common when autonomic dysfunction was present (2.3% vs 1.5%).

LEMS should be suspected in patients diagnosed as MG with autonomic dysfunction, especially in those with SCLC. Based on our analyses, at least 2% of this MG population may actually have the diagnosis of LEMS and be appropriate for alternative treatments.