Lambert-Eaton myasthenic syndrome (LEMS) is a rare disease in which the immune system mistakenly attacks the nerve cell endings that convey messages to muscles. This results in progressive muscle weakness in the legs, arms, hips, and shoulders, which can limit mobility.
How are nerve signals sent?
Normally, when the brain sends a nerve signal from the brain to the muscles, it is sent as an electrochemical signal. At the end of the nerve cell where it interacts with muscle (the neuromuscular junction), the electrical signal is converted into a chemical message. The nerve cell ending releases a neurotransmitter or signaling molecule called acetylcholine into the neuromuscular junction. Acetylcholine binds to receptors found on the other side of the junction, i.e. on the muscle cell carrying the message across and signaling the muscle to contract.
After the nerve signal has been sent, enzymes called cholinesterases break down excess acetylcholine in the neuromuscular junction, resetting the junction so that it is ready to receive the next message.
In LEMS, the immune system attacks the nerve cell endings, meaning that nerve signals are weaker. Without stimulation from the nervous system, muscles weaken and atrophy as the disease progresses.
What are cholinesterase inhibitors?
Cholinesterase inhibitors are chemicals that block the enzyme that breaks down acetylcholine. When cholinesterase inhibitors are present, acetylcholine lingers in the neuromuscular junction instead of being cleared immediately. This means that a stronger, longer-lasting nerve signal can be sent.
Cholinesterase inhibitors for LEMS
Cholinesterase inhibitors have not been approved to treat LEMS specifically, but may be prescribed off-label. They are usually only mildly effective in treating LEMS, but for some patients, this is sufficient to manage the symptoms of the disease.
Pyridostigmine is the most commonly used cholinesterase inhibitor for LEMS.
Other cholinesterase inhibitors include:
Cholinesterase inhibitors can cause side effects such as diarrhea, abdominal cramps, and excessive saliva production.
Last updated: Oct. 16, 2019
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