Lambert-Eaton syndrome, according to the authors who described the disease in 1966, is a myasthenic syndrome.
Clinically we observe intermittent muscular weakness (i.e. strength improvement after exercise) which predominantly affects proximal muscles from thighs or hips, more rarely ocular muscles (different from genuine myasthenia), reduction of reflexes, and autonomic dysfunction such as mouth dryness (often the initial presenting symptom). The respiratory muscles are rarely involved.
Most cases of Lambert-Eaton syndrome are seen as a paraneoplastic diseases (50% of cases, mainly associated with lung cancers) or in auto-immune diseases (rheumatoid arthritis, lupus).
In cancer, the syndrome is related to the release, by cancer cells, of various proteins (synaptotagmin, syntaxin) which are present at the neuromuscular synapse. Autoantibodies (mainly IgG) which alter the transmission of the nervous influx are then produced.
Sanders DB: Lambert-Eaton myasthenic syndrome: clinical diagnosis, immune-mediated mechanisms, and update on therapies. Ann Neurol 1995 May; 37 Suppl 1: S63-73
See also : Lambert-Eaton Myasthenic Syndrome in e-Medicine