Charcot-Marie-Tooth disease (CMT) is a group of disorders characterized by progressive damage to the peripheral nervous system. Peripheral nerves are those that carry electrical signals from the brain to the muscles to control movement and sensory information — like feeling cold or heat — from the body to the brain.
What are muscle relaxants?
Muscle relaxants are therapies that can reduce the frequency and severity of muscle cramps. In a study in 110 people with CMT, 23 percent reported having daily muscle cramps, and 22 percent indicated that these cramps had a negative effect on their quality of life.
For muscles to move, a nerve signal is sent from the brain via nerve cells called motor neurons and received by muscle cells. The point at which a nerve cell meets a muscle cell is called the neuromuscular junction. At this junction, a chemical signal such as acetylcholine is released by the nerve cell and binds to receptors found on the muscle cell, allowing it to contract and initiate movement. Once the message has been sent, acetylcholine is cleared and the muscle relaxes.
There are two types of muscle relaxants: depolarizing and non-depolarizing. Depolarizing muscle relaxants act on the acetylcholine receptors, activating them artificially. However, because they cannot be cleared by the mechanisms that normally clear acetylcholine, they cause the muscle cell to become unresponsive and relax.
Non-depolarizing muscle relaxants bind to and inhibit the acetylcholine receptor without activating it. They prevent acetylcholine from binding to its receptor because these receptors are already bound to the inhibitor and not available to bind acetylcholine. In this way, muscles stay relaxed.
CMT patients are advised to avoid depolarizing muscle relaxants since they can have a very prolonged effect.
Muscle relaxants for CMT
Baclofen and dantrolene are muscle relaxants that may be prescribed for CMT patients. Benzodiazepines such as diazepam may also be prescribed, though there is a risk of developing a dependence on this type of medication. Moreover, benzodiazepines can cause dizziness, which may increase patients’ risk of falling.
Mexiletine, a medication used to treat heart arrhythmias is also being investigated as a muscle relaxant in patients with CMT.
Muscle relaxants are used during surgery in combination with anesthesia to prevent patients from feeling pain. It is important that CMT patients inform their surgical team of their disease, as they may respond differently to anesthesia than others do.
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