Clinical, Pathophysiological and Electrodiagnostic Aspects of Lambert-Eaton Myasthenic Syndrome

Abstract

Lambert-Eaton myasthenic syndrome (LEMS) is characterized by an autoimmune disorder of the neuromuscular junction, which, through a reduction in nerve terminal acetylcholine release mediated by antibodies against functional voltage-gated calcium channels (VGCCs) of the P/Q in presynaptic nerve terminals, leads to proximal muscle weakness, in addition to autonomic dysfunction and areflexia, constituting the classic triad of symptoms. The syndrome presents itself in two forms: the paraneoplastic form—resulting mainly from small cell lung carcinoma—and the underlying autoimmune form. With clinical suspicion of the disease, the diagnosis can be made through serological and electrophysiological tests, which present typical findings and reflect the existence of a presynaptic transmission defect. Treatment is based on early screening and removal of the etiological agent, which in the most common case is the treatment of the underlying cancer. In patients whose symptoms affect their daily activities, some medications can intervene in the search for a better quality of life, such as amifampridine, pyridostigmine and 3,4-diaminopyridine (3,4-DAP). It must be remembered, however, that LEMS has a significant impact on the patient’s quality of life and ability to perform daily activities and therefore warrants timely diagnosis and adequate treatment in itself.