Lambert-Eaton myasthenic syndrome (LEMS)

Lambert-Eaton myasthenic syndrome also affects the neuromuscular junction, and the trouble sits on the nerve side of that connection. In most people, antibodies target voltage-gated calcium channels on the presynaptic nerve terminal, which reduces the release of acetylcholine, the chemical messenger that triggers muscle contraction. A large share of cases occur as a paraneoplastic syndrome linked to an underlying cancer, most often small-cell lung cancer, so a new diagnosis usually prompts cancer screening, and other cases arise as a primary autoimmune condition without a tumor. LEMS is considered a rare condition.

Research describes an annual incidence estimated between roughly 0.09 and 0.3 per million people and an overall prevalence around 1 per million, with a median age at diagnosis near 60 and a slight female predominance.

Common signs

Weakness that tends to start in the hips and thighs, making it hard to rise from a chair or climb stairs, along with autonomic symptoms such as dry mouth, constipation, and lightheadedness. Reflexes are often reduced, and unlike myasthenia gravis, strength may briefly improve with a short burst of activity before fatiguing again, a pattern called post-exercise facilitation.

This is a plain-language summary for orientation, not a diagnosis. Mechanisms are described as current understanding, not settled fact. Work with your own clinician for your care.