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Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder which affects calcium channels of the nerve-muscle (neuromuscular) junction. The etiology of LEMS may resemble myasthenia gravis, but there are substantial differences between the clinical presentation and pathogenetic features of the two disorders.
While children and young adults may be affected, the disease is usually observed in middle aged and older individuals. The incidence of the disease is difficult to determine due to its low frequency.
Anderson was the first person to mention a case with possible clinical findings of LEMS in 1953, but Lambert, Eaton and Rooke were the first physicians to substantially describe the clinical and electrophysiological findings of the disease in 1966.[1][2]
It is usually associated with auto-immune self antibodies to the pre-synaptic voltage gated calcium channels,[3] which leads to neuromuscular block.
While LEMS may be found as a solitary disease, 50% of cases have an associated malignancy. Malignancies that may be found with LEMS may include small-cell lung cancer, lymphoma, non-Hodgkin’s lymphoma, T-cell leukemia, non-small cell lung cancer, prostate cancer, and transitional cell carcinoma of the bladder. The myasthenic syndrome associated with thymoma is actually true myasthenia gravis, where weakness worsens with repeated activity (as opposed to LEMS, where weakness improves with repeated activity).[4]
Whether solitary or cancer-associated, the disease is believed to be of autoimmune origin. In 1989, the previously anticipated antibodies were demonstrated to be directed against presynaptic calcium channels, which are located in neuromuscular junction (see synapse) and are responsible for the presynaptic release of acetylcholine. The calcium channel antibodies prevent the opening of calcium channels and thus prevent the release of acetylcholine.
There are some patients that do not carry these antibodies in their serum samples and the exact cause of disease in these cases still remains to be determined.[citation needed] In cases with both LEMS and lung cancer (usually small cell type), the antibodies are suggested to be aimed at cancer cells and to bind and affect the antigens in neuromuscular junction accidentally.
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