The Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease of neuromuscular transmission in which autoantibodies against the P/Q-type voltage-gated calcium channel (VGCC) at the presynaptic nerve terminal play a major role in decreasing quantal release of acetylcholine (ACh). Clinically, LEMS patients suffer from characteristic muscle weakness and autonomic symptoms. The underlying cause of LEMS in slightly more than half of all patients is small cell lung carcinoma (SCLC) [DS:H00013]. The nerve terminal and carcinoma cells apparently share a common antigen (VGCC), suggesting an immunological cross-reactivity that may lead to the neurological abnormality. Cancer therapy is the priority for these patients. As for the remaining cases, no antibodies to P/Q-type VGCCs have been found in 10-15% of patients with LEMS. The fact that these seronegative patients positively respond to immunotherapy leads to the presumption that antibodies to other proteins might play a role in LEMS. Diagnosis of LEMS is ascertained on the basis of clinical symptoms and is further supported by electrophysiological and serological tests. The clinical triad in LEMS consists of weakness predominantly affecting proximal muscle groups, autonomic dysfunctions, and areflexia. Besides oncological treatment in case of SCLC-LEMS, treatment is based on symptomatic and semi-specific immunosuppressive therapy.
Lambert-Eaton myasthenic syndrome: search for alternative autoimmune targets and possible compensatory mechanisms based on presynaptic calcium homeostasis.
