Lambert-Eaton myasthenic syndrome (LEMS)

Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular disorder in which autoantibodies inhibit the presynaptic release of acetylcholine. Autoantibodies against P/Q-type voltage-gated calcium channels (VGCC) are detected in 85% of patients with LEMS. In addition, autoantibodies to synaptotagmin, an M1-type muscarinic acetylcholine receptor and SOX1 are also found in the sera of patients with LEMS. LEMS is closely associated with small cell lung cancer (SCLC) in 50-60% of patients. Patients with SCLC who have anti-VGCC antibodies have been reported to have a favorable prognosis. In contrast to paraneoplatic LEMS, other forms of LEMS may have an autoimmune aspect because of the established association between human leukocyte antigen and a family history of other autoimmune disorders in this condition. The clinical features of LEMS include proximal weakness, areflexia, ptosis, cerebellar ataxia and autonomic dysfunction. The findings of electrophysiological examination show that LEMS is characterized by compound muscle action potential potentials with a low amplitude and increment upon repetitive nerve stimulation at a high rate. Tumor removal is the primary treatment of LEMS. The efficacy of 3,4-diaminopyridine for the treatment of LEMS has also been established. Patients with LEMS require the immunotherapies such as plasma exchange and the administration of high doses of immunoglobulin and prednisolone.