Eaton-Lambert syndrome is an autoimmune disorder that impairs communication between nerves and muscles, causing weakness.
Nerves communicate with muscles by releasing a chemical messenger (neurotransmitter), which interacts with receptors on muscles (at the neuromuscular junction—see Overview of Neuromuscular Junction Disorders) and stimulates muscles to contract. Eaton-Lambert syndrome is caused by antibodies that interfere with the release of the neurotransmitter acetylcholine rather than attack acetylcholine receptors (as occurs in myasthenia gravis—see Myasthenia Gravis). Eaton-Lambert syndrome usually precedes, occurs with, or develops after certain cancers. It most commonly occurs in men with tumors in their chest, especially lung cancer.
Eaton-Lambert syndrome causes muscle weakness that tends to affect the larger muscles in the arms and, particularly, the legs. Typically, people have difficulty getting up from a chair, climbing stairs, and walking. Muscles may become weaker or cramp after they are used repeatedly. People also tire easily.
The mouth is dry, the eyelid droops, and the upper arms and thighs are painful.
Men may have erectile dysfunction.
Symptoms suggest the diagnosis, but electromyography (stimulating muscles, then recording their electrical activity) is needed to confirm the diagnosis.
Treating cancer, if present, sometimes relieves symptoms due to Eaton-Lambert syndrome.
Guanidine, a drug that increases the release of acetylcholine, often lessens symptoms but may inhibit the bone marrow's production of blood cells and impair liver function.
Corticosteroids and plasma exchange (filtering of toxic substances, including abnormal antibodies, from the blood) help some people.
Last full review/revision December 2014 by Michael Rubin, MDCM