Lambert-Eaton myasthenic syndrome (LEMS)

Lambert-Eaton myasthenic syndrome (LEMS), also known as Lambert-Eaton syndrome (LES), is a rare autoimmune neuromuscular disorder in which the immune system mistakenly attacks voltage-gated calcium channels (VGCCs) at the neuromuscular junction, where nerves communicate with muscles. This reduces the release of acetylcholine, making it more difficult for muscles to contract, leading to muscle weakness, fatigue, and other symptoms.

Although both forms are caused by an autoimmune attack on the neuromuscular junction, identifying whether LEMS is associated with an underlying cancer is important because it affects treatment and prognosis.

Muscle weakness (especially affecting the hips and thighs), muscle fatigue that may temporarily improve after brief exercise, difficulty climbing stairs or rising from a chair, dry mouth, constipation, dry eyes, erectile dysfunction, reduced sweating, decreased or absent tendon reflexes, eyelid drooping (ptosis), double vision, difficulty speaking (dysarthria), difficulty swallowing (dysphagia), and tingling or numbness in the hands and feet. Symptoms usually develop gradually but may progress more rapidly in people whose LEMS is associated with small cell lung cancer.

Approximately 50–60% of people with LEMS have small cell lung cancer (SCLC). Less commonly, LEMS has been associated with other cancers such as thymoma and prostate cancer. People with non-paraneoplastic LEMS are also more likely than the general population to have other autoimmune diseases, including autoimmune thyroid disease, type 1 diabetes, vitiligo, rheumatoid arthritis, and pernicious anemia.

Risk factors vary depending on the type of LEMS:

Paraneoplastic LEMS

Small cell lung cancer

Cigarette smoking

Older age

Male sex

Non-paraneoplastic LEMS

Genetic susceptibility involving certain human leukocyte antigen (HLA) genes

Personal or family history of autoimmune disease

Lambert-Eaton myasthenic syndrome (LEMS) is a rare disease with an estimated prevalence of approximately 2–3 people per million people. Paraneoplastic LEMS most commonly develops in older adults and is more common in men, whereas non-paraneoplastic LEMS can occur at any age and is somewhat more common in women.