For patients with Lambert-Eaton myasthenic syndrome (LEMS) or myasthenia gravis, getting a diagnosis can be challenging. The symptoms of both autoimmune diseases are similar, so blood tests for specific antibodies may be necessary to confirm a diagnosis.
What is myasthenia gravis?
Myasthenia gravis is an autoimmune disease in which the immune system produces antibodies against components of the neuromuscular junction — the junction between nerve cells and muscles. These autoantibodies damage the connections, causing progressive muscle weakness.
In order to send nerve signals to muscles, the nerve depolarizes — shuttling ions inside and out of the cell to change its overall electrical charge and send an electrical signal down the nerve. At the neuromuscular junction, the electrical charge tells the end of the nerve to release a chemical called acetylcholine, which binds to the acetylcholine receptor situated on the other side of the junction and signals the muscle to contract through a series of chemical reactions which are propagated by a receptor-associated protein called muscle-specific tyrosine kinase (MuSK).
Myasthenia gravis develops as a result of the body producing antibodies against either MuSK or the acetylcholine receptor.
What is LEMS?
LEMS is an autoimmune disease in which the body produces autoantibodies against a calcium channel in the nerve cells which controls the release of acetylcholine.
Without the calcium channels, the nerve cells cannot release enough acetylcholine, which causes muscle weakness.
Other disease differences
About 3% to 8% of myasthenia gravis patients develop a thyroid condition, which they should be tested for as soon as their doctor suspects myasthenia gravis.
About 50% to 60% of LEMS patients have small-cell lung cancer, which should be tested for as soon as LEMS is suspected.
No cure is available for either disease, but treatments can help manage symptoms.
For LEMS patients, chemotherapy for small-cell lung cancer (if present) comes ahead of treating muscle weakness.
For both LEMS and myasthenia gravis, the treatments are targeted at suppressing the immune response (to reduce autoantibody production) and increase acetylcholine production to create a stronger muscle response to nerve signals.
Last updated: Oct. 20, 2019
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