Objective: To improve the understanding of cinical manifestations, electromyographic (EMG)characteristics and treatments of Lambert-Eaton myasthenic syndrome(LEMS).

Methods: The clinical diagnosis and treatment process of one LEMS was reported. The clinical manifestations, subtypes, EMG characteristics, diagnosis, treatment and prognosis of LEMS were focused with literature review.

Results: One elderly female patient complained of recurrent and fluctuating systemic weakness for more than 6 years and worsening for half a year. She successively tested positive for anti Mal and anti lgLON5-lgG antibodies, and multiple negative screenings for tumors. EMG suggested neuromuscular junction disease, highlighting the possibility of anterior membrane disease, and LEMS was considered.

Conclusion: LEMS is a rare disease, which has often been reported to be associated with tumors, especially small cell lung cancer. The patient was negative for multiple tumor screenings, but positive for anti Ma1 and anti lgLON5-lgG antibodies, it suggested that the immune factors may contribute for the pathogeny. The amplitude change of repetitive nerve stimulation is the electrophysiological gold standard for diagnosing LEMS, early test and correct diagnosis, as well as active immunomodulatory therapy are the key to this disease.