Lambert-Eaton Myasthenic Syndrome (LEMS)

Signs and Symptoms

Lambert Eaton myasthenic syndrome (LEMS) is a rare neuromuscular disorder that weakens and fatigues the body's voluntary muscles (those we can move at will). Unlike myasthenia gravis (MG), it may also cause mild involvement of the autonomic nervous system, a part of the nervous system that is beyond the ability of the individual to control. Like MG, LEMS does not affect the heart or major organs unless there is an associated cancer which can influence the symptoms.

LEMS typically causes weakness in the upper legs and hips more than the upper arms and shoulders. In some cases, muscle fatigue and heaviness may be more prominent than actual weakness. Common difficulties include standing from a chair, climbing stairs, walking, or running. Arm tasks like lifting and pushing may also be affected. Like MG, LEMS can cause mild eyelid drooping (ptosis) and occasionally double vision (diplopia), as well as weakness in the face, and sometimes in muscles used for chewing, swallowing, or breathing. Autonomic symptoms, such as dry mouth and erectile dysfunction in men can also occur.

About half of those with LEMS have or will develop cancer, typically small cell lung cancer. Most of these individuals are smokers. The other half have LEMS without cancer, and this form can occur across a wide age range, though often in younger adults.

Disease course

The proximal weakness in LEMS is slowly progressive. Weakness and fatigue can fluctuate from day to day. Stress, heat and lack of sleep may make symptoms worse. Medications (see Medical Management) can help in the management of disease. Over the long term, people without cancer usually do well with treatment, but most continue to have some symptoms. Breathing or swallowing problems are relatively rare and tend to occur with advanced cases. When LEMS occurs with cancer, the overall course depends largely on how the cancer behaves.

Additional reading

• Kesner VG, Oh SJ, Dimachkie MM, Barohn RJ. Lambert-Eaton Myasthenic Syndrome. Neurol Clin. 2018 May;36(2):379-394. doi: 10.1016/j.ncl.2018.01.008. PMID: 29655456; PMCID: PMC6690495.
• Titulaer MJ, Lang B, Verschuuren JJ. Lambert-Eaton myasthenic syndrome: from clinical characteristics to therapeutic strategies. Lancet Neurol. 2011 Dec;10(12):1098-107. doi: 10.1016/S1474-4422(11)70245-9. PMID: 22094130.
• Varon MC, Dimachkie MM. Diagnosis and treatment of Lambert-Eaton myasthenic syndrome. Practical Neurology (US). 2024;23(3):26-28,47.

Last revised December 2025.