If you or someone you know has myasthenia gravis (MG), you may be familiar with how muscle weakness can fluctuate. The muscles tend to tire easily with use, but often improve after rest. Learning why this cycle occurs can help make a complex disease a little easier to understand.
Acetylcholine: Nerve messengers without a catcher
The reason why muscle weakness fluctuates in MG (as opposed to being static) has everything to do with how nerves communicate with the muscles and how MG interrupts that normal flow of information.
Nerves communicate with muscles via a transmitter known as acetylcholine. For the muscles to receive signals from the nerves, they need to have specialized proteins called acetylcholine receptors. When everything is working correctly, these receptors capture the acetylcholine signal sent from the nerves, which starts a process that causes the muscles to contract.
In MG, however, the body produces antibodies that destroy these acetylcholine receptors. This in effect means that there are fewer “catchers” to receive the signals sent from the nerves to the muscles.
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From muscle activity to muscle weakness
Since acetylcholine receptors are destroyed by antibodies in MG, acetylcholine levels are the determining factor for how much communication goes on between the nerves and the muscles.
When the muscles are repeatedly used, the nerves release less and less acetylcholine to the muscles each time. This creates a scenario in which there are not only insufficient acetylcholine receptors, but insufficient acetylcholine, as well. Less acetylcholine means it’s even less likely the remaining acetylcholine receptors will capture any.
When this happens, the muscles cannot respond as well to the nerves. The body interprets this as muscle weakness. This explains why repetitive muscle activity, such as climbing a flight of stairs, can become more and more tiring as time progresses.
With rest, acetylcholine levels can be partially replenished. When these levels go back up, muscle weakness improves. This is why muscle strength can be partially restored after rest, and patients feel their energy and strength levels go up and down.
Understanding your body
Every patient has different experiences with fluctuations in muscle weakness. Some patients find that they recover more quickly, while others require a longer period of rest after physical exertion. This is why it’s important to understand your own body and adjust to its rhythms.
Medication, lifestyle changes and physical therapy can all help improve fluctuating muscle weakness, so speak to your doctor if you find that you’re not coping well with how these changes affect your daily life.
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