C Lambert-eaton myasthenic syndrome
Incidence
Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disease that classically occurs in patients with malignant disease, particularly small cell carcinoma of the bronchi. One-third to half of patients, however, have no evidence of carcinoma. Most patients with myasthenic syndrome are men between the ages of 50 and 70 years.
Pathophysiology
The basic defect associated with LEMS appears to be an autoantibody-mediated derangement in presynaptic Ca2+ channels leading to a reduction in Ca2+-mediated exocytosis of acetylcholine (ACh) at neuromuscular and autonomic nerve terminals. The decreased release of ACh quanta from the cholinergic nerve endings produces a reduced postjunctional response. Unlike in myasthenia gravis, the number and the quality of postjunctional AChRs remain unaltered, and the end plate sensitivity is normal. The neuromuscular junction abnormality of LEMS is similar in location to that of Mg2+ intoxication or botulism poisoning, in which the release of presynaptic ACh is attenuated.
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