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Lambert-Eaton myasthenic syndrome and slow channel syndrome Masakatsu Motomura 1 1First Department of Internal Medicine, Graduate School of Biochemical Sciences, Nagasaki University Keyword: チャネロパチー , Lambert-Eaton筋無力症候群 , LEMS , P/Q型電位依存性カルシウムチャネル(P/Q型VGCC)抗体 , スローチャネル症候群 , SCS , 先天性筋無力症候群 pp.291-303
Published Date 2003/4/10
DOI https://doi.org/10.11477/mf.1431100310
  • Abstract
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 The Lambert-Eaton myasthenic syndrome(LEMS)and slow channel syndrome(SCS)are representative channelopathies of the neuromuscular junction. Both diseases are diagnosed by characteristic clinical signs and electrical findings and are amenable to treatment. LEMS is an autoimmune disorder in which IgG autoantibodies lead to presynaptic P/Q-type voltage-gated calcium channel(VGCC)loss. As a paraneoplastic disorder, 60%of patients with LEMS have samll cell lung carcinomas(SCLC)that express functional VGCCs. Recent results strongly suggest that the antibodies to P/Q-type VGCC are the principal pathogenic factors in LEMS. Here, we present pathophysiology and treatment of LEMS patients. Proximal weakness, depressed tendon reflexes, autonomic symptoms, and electrical posttetanic potentiation together are essential to accurately diagnose LEMS. The diagnosis is established immunologically by the presence of anti-P/Q-type VGCC antibodies, detected using the 125I-ω-conotoxin MVIIC radioimmunoassay, which will be present in 85%of LEMS patients. The remaining 15%of patients are classified as seronegative. Except for the indication that SCLC is less common in seronegative patients, no significant differences were found in the clinical characteristics of patients who had or did not have P/Q-type VGCC antibodies. At present, there is no report of a congenital LEMS patient whose P/Q-type VGCC gene has genetic mutations. On the other hand, the slow channel syndrome is a hereditary disease caused by mutations in the subunits of the acetylcholine receptor that prolong the opening time of the acetylcholine-induced ion channel. The clinical diagnosis of SCS is suggested by a positive family history, specific muscle weakness, the decremental response to repetitive nerve stimulation in clinically affected muscles, and the repetitive compound muscle action potential to a single nerve stimulus. Recently, a couple of studies reported a patient with clinical and electrophysiological features of SCS and positive AChR antibodies and suggested that AChR antibodies altered the function of AChR, and this new form of myasthenia gravis was termed acquired SCS.


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電子版ISSN 1882-1243 印刷版ISSN 0001-8724 医学書院

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