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This chapter describes the disorders of neuromuscular transmission (DNMT) other than myasthenia gravis (MG) (Table 26-1). The neuromuscular junction (NMJ) is a physiologically complex structure. Its ability to function optimally requires the integration of a large number of proteins including ion channels that are correctly configured and distributed. As a result of numerous potential sites of vulnerability, DNMTs may occur as a consequence of multiple, albeit infrequent disorders. Autoimmune, genetic, or toxic mechanisms may disrupt the ultrastructure or physiology of the NMJ, thus interfering with effective NMT.
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LAMBERT–EATON MYASTHENIC SYNDROME
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The Lambert–Eaton myasthenic syndrome (LEMS) can be conceptualized as an acquired presynaptic DNMT typically presenting with symptoms of proximal lower extremity weakness and fatigue. The first single case description of LEMS was provided by Anderson in 1953. Its eponym however is credited to Edward Lambert and Lee Eaton who along with Edward Rooke described in 1956 the electrophysiological as well as clinical characteristics of the disorder in six cases.1,2 LEMS is a rare disorder with an estimated incidence of 1 and prevalence of 3.5 per million people.1–10 LEMS is largely a disease of adults although rare pediatric cases have been described [both acquired autoimmune condition and as a congenital myasthenic syndrome (CMS)].11 LEMS is paraneoplastic disorder in many cases, but can be seen as a primary autoimmune disorder without an underlying cancer. The epidemiology between those cases of LEMS associated with a malignancy differs from those cases without an underlying neoplasm. Nonneoplastic LEMS appears to have two peaks, 35 and 60 years of ...