The Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune presynaptic disorder of neuromuscular transmission in which antibodies are directed against the voltage-gated calcium channel. The classic clinical features include proximal muscle weakness, depressed deep tendon reflexes, and prominent symptoms of autonomic dysfunction. The hallmark electrophysiological finding is a reduction in the size of the compound muscle action potential with facilitation (i.e., increased in amplitude) following brief sustained muscle contraction. In many patients, LEMS may occur in association with an underlying malignancy as a paraneoplastic disorder. How frequently are these clinical and electrophysiological features encountered in patients with LEMS? How specific is the finding of compound muscle action potential facilitation for the diagnosis? Is the presence of antibodies against voltage-gated calcium channels specific for LEMS? Should patients with LEMS be treated with immunosuppressive therapy notwithstanding the frequency with which underlying malignancies are detected? What is the long-term prognosis of LEMS, and does the presence of LEMS affect the prognosis for patients with small cell lung carcinoma? These and other questions are the subject of this chapter.
KeywordsAmyotrophic Lateral Sclerosis Maximal Voluntary Contraction Plasma Exchange Small Cell Lung Carcinoma Compound Muscle Action Potential
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