Myasthenia gravis (MG) is a rare neuromuscular disease. The medical term is translated as “severe muscle weakness”. In the United States, an estimated 30,000 to 60,000 people suffer from this disease, which affects people of all ages, genders, and races.Recently updated Consensus guidelines We have increased our understanding of the different forms of myasthenia gravis and improved treatment methods.
What are the symptoms of myasthenia gravis?
Myasthenia gravis In a location called the neuromuscular junction (NMJ), the transmission of signals from the nerve to the muscle is impaired, where the nerve contacts the muscle. This can cause temporary weakness of the muscles in use. When the affected muscle or muscle group rests, it can regain strength.
Throughout the day, your body uses many muscle groups repeatedly. Even if you are not particularly active, this is correct. Because myasthenia gravis is characterized by use-related weakness in a specific muscle group, repeated activity of the affected muscle can exacerbate the weakness. Rest can improve weakness, and can only recover after resuming activity.
The affected muscle groups may vary from person to person. Usually, the muscles around the eyes are affected. Drooping eyelids and diplopia are common symptoms. People may complain that they are fine when they wake up, but over time, their eyelids droop. After a nap, their eyes opened wide. They may see a good driving experience at first, but when they continue to drive, they will have a double vision. They cannot eat whole bagels because their jaws will get tired after a while, even though they can eat pasta without problems. They feel tired when their hair is blown dry, and they must stop, put their arms down for a while, and then continue.
What causes myasthenia gravis?
Several diseases and even certain drugs can affect neuromuscular connections. I will focus here on a type of myasthenia gravis called autoimmune myasthenia gravis. If you have autoimmune MG, your immune system will produce antibodies that can inappropriately attack certain proteins at the junction. One such protein is the acetylcholine receptor (AchR), located on the muscle membrane at the junction.
This specific protein binds to a chemical messenger called acetylcholine (Ach). When the electrical signal reaches the nerve ending, Ach is released, causing the muscle to contract. But AchR antibody destroys AchR and reduces the amount of AchR, which weakens the transmission of impulses from nerves to muscles and causes muscle weakness.
Antibodies may also target other important proteins at the neuromuscular junction, which usually help maintain the AchR protein, leading to the same end result. Two such proteins that antibodies may target are muscle-specific kinase (MuSK) and lipoprotein-related protein 4 (LRP-4).
How is myasthenia gravis treated?
Treatment is first aimed at improving symptoms. The most commonly used drug is pyridostigmine. Pyridoxine prolongs the time that Ach stays in the neuromuscular junction, thus giving it more opportunities to bind to the reduced number of AchR receptors.
In addition, people with autoimmune MG will receive treatment to suppress the abnormal immune response behind the disease. Many methods are used to achieve this.
In 2016, the Myasthenia Gravis Foundation (MGFA) convened an international task force composed of neuromuscular experts to develop guidelines for treatment.The team updated the guide in 2020, adding New suggestion Used in a surgical procedure called thymectomy; treatment of eye MG (only MG in the muscles around the eye); and use of three drugs to deal with abnormal immune responses: methotrexate, rituximab and ecu Lizumab.
- Thymectomy The thymus is located in the upper middle chest between the lungs and is believed to play a role in the autoimmune response of MG. In thymectomy, the glands are removed surgically.A kind Randomized controlled trial The results show that thymectomy can effectively reduce the dose of prednisone (an immunosuppressive drug) required by specific MG patients.
- Methotrexate Did not reduce the need for prednisone Randomized controlled trial MG population with AchR antibody.
- Rituximab According to the consensus report, it is helpful for patients with MuSK MG, but not for patients with AchR MG.
- Eculizumab Is a new drug with a novel mechanism of action, Improve physical function People whose MG has not responded to previous treatments. Meningococcus (a group of bacteria that cause meningitis) must be immunized before treatment. Eculizumab is injected intravenously once a week for five weeks, and then every two weeks after this initial period.
Many people with autoimmune MG require long-term immunosuppressive treatment to help them control the disease. The best treatment options are determined by monitoring the course of the disease and response to treatment.
The treatment of MG is complicated. Your neurology team will consider multiple factors, including age, gender, pregnancy and breastfeeding, and other medical conditions (such as high blood pressure, diabetes, or liver disease). They will also consider the existence and type of MG antibodies, the type of MG you encounter (eye MG or generalized MG, its scope of influence is not limited to the eyes), but also your preferences and values.
When you get new information about treatment, discuss possible treatment changes with your neurologist, who can help ensure that the treatment choices you make are consistent with your improvement goals and your personal values and preferences.