Lambert-Eaton myasthenic syndrome.
The Lambert-Eaton Myasthenic Syndrome (LEMS) is characterised by proximal muscle weakness initially affecting gait, autonomic symptoms (dry mouth, constipation, erectile failure), augmentation of strength during initial voluntary activation, and depressed tendon reflexes with post-tetanic potentiation. The disorder is paraneoplastic (small cell lung cancer) in about 60p. cent (P-LEMS); no cancer is associated in the remainder (NP-LEMS). LEMS affects all races. NP-LEMS can occur in childhood as well as adult life; P-LEMS is unusual at<30 Years. The weakness results from a reduction in the quantal release of acetylcholine from motor nerve terminals, caused by autoantibodies to P/Q-type voltage-gated calcium channels (VGCCs) that are provoked by tumour VGCCs in P-LEMS; the stimulus in NP-LEMS is not known. These antibodies may be implicated in the rarely associated cerebellar degeneration. The diagnosis can be confirmed by detecting the specific antibody in a radioimmunoprecipitation assay, and by finding a reduced compound muscle action potential amplitude that increases by>100p. cent following maximum voluntary activation. Most patients benefit from 3,4-diaminopyridine; pyridostigmine is less effective. Specific tumour therapy in P-LEMS will often ameliorate the neurological disorder. In those with severe weakness, IVIg or plasmapheresis confers short-term benefits. Prednisone alone or combined with azathioprine or cyclosporin can achieve long-term control of the disorder.
Newsom-Davis
J
J
Department of Clinical Neurology, University of Oxford, Grande-Bretagne. john.newsomdavis@btinternet.com
D015761:4-Aminopyridine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D000077770:Amifampridine; D001323:Autoantibodies / Q000276:immunology; D001324:Autoantigens / Q000276:immunology; D020274:Autoimmune Diseases of the Nervous System / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology / Q000628:therapy; D020865:Calcium Channels, P-Type / Q000276:immunology; D020907:Calcium Channels, Q-Type / Q000276:immunology; D018288:Carcinoma, Small Cell / Q000150:complications / Q000276:immunology; D002800:Cholinesterase Inhibitors / Q000627:therapeutic use; D006801:Humans; D016756:Immunoglobulins, Intravenous / Q000627:therapeutic use; D007166:Immunosuppressive Agents / Q000627:therapeutic use; D015624:Lambert-Eaton Myasthenic Syndrome / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology / Q000628:therapy; D008175:Lung Neoplasms / Q000150:complications / Q000276:immunology; D009363:Neoplasm Proteins / Q000276:immunology; D010956:Plasmapheresis; D026902:Potassium Channel Blockers / Q000627:therapeutic use; D011729:Pyridostigmine Bromide / Q000627:therapeutic use
D001323:Autoantibodies; D001324:Autoantigens; D020865:Calcium Channels, P-Type; D020907:Calcium Channels, Q-Type; D002800:Cholinesterase Inhibitors; D016756:Immunoglobulins, Intravenous; D007166:Immunosuppressive Agents; D009363:Neoplasm Proteins; D026902:Potassium Channel Blockers; D015761:4-Aminopyridine; D011729:Pyridostigmine Bromide; D000077770:Amifampridine