Myasthenia gravis (MG) – a medical term translated as “severe muscle weakness” – is a rare neuromuscular disease. An estimated 30,000 to 60,000 people in the United States have this disorder, which affects people of all ages, genders, and ethnicities. Recently updated consensus guidelines have expanded our knowledge of various forms of myasthenia gravis and improved treatment approaches.
Living with Myasthenia Gravis.
Myasthenia gravis affects the transmission of signals from nerves to muscles in a location called the neuromuscular junction (NMJ), where nerves make contact with muscles. This leads to temporary muscle weakness. When the affected muscle or muscle group is rested, it regains strength.
Your body uses many muscle groups repeatedly throughout the day. This also applies if you are not particularly active. Because myasthenia gravis is characterized by weakness in certain muscle groups due to use, repeated activity of the affected muscle makes the weakness worse. The weakness improves with rest and occurs again when activity is resumed.
Which muscle groups are affected can vary from person to person. Often the muscles around the eyes are affected. Drooping eyelids and double vision are common symptoms. People may complain that they are fine when they wake up, but their eyelids droop as the day progresses. After a nap, her eyes are wide open. You might start to see well while driving, but as you keep driving you develop double vision. You can’t eat a whole bagel because your jaw gets tired after a while, although you can eat pasta without any problems. Their arms get tired after blow drying their hair and they need to stop, put their arms down for a while and then move on.
What causes myasthenia gravis?
Various disorders and even some drugs can affect the neuromuscular junction. I’m going to focus here on a form of myasthenia gravis called autoimmune MG. When you have autoimmune MG, your immune system produces antibodies that inappropriately attack certain proteins at the junction. One such protein is the acetylcholine receptor (AchR), which is located at the junction on the muscle membrane.
This special protein binds to a chemical messenger called acetylcholine (Ach). Ach is released from the nerve ending when an electrical signal reaches it, causing a muscle to contract. However, AchR antibodies destroy and reduce the number of AchR, so that the transmission of impulses from the nerve to the muscle is impaired and muscle weakness occurs.
Antibodies can also be directed against other important proteins at the neuromuscular junction that would normally help preserve AchR proteins, causing the same end result. Two such proteins that antibodies can target are muscle specific kinase (MuSK) and lipoprotein-related protein 4 (LRP-4).
How is myasthenia gravis treated?
Treatment is initially aimed at improving symptoms. The most commonly used drug is pyridostigmine. Pyridostigmine increases the time Ach remains in the neuromuscular junction, giving it a greater chance of binding to the reduced number of AchR receptors.
In addition, people with autoimmune MG are given treatment to suppress the abnormal immune response underlying the disease. Many approaches are used to achieve this.
In 2016, the Myasthenia Gravis Foundation of America (MGFA) convened an international task force of neuromuscular specialists to develop guidelines for treatment. This panel updated these guidelines in 2020, adding new recommendations for a surgical procedure called thymectomy. Treatment of eye MG (MG limited to the muscles around the eyes); and the use of three drugs to treat an abnormal immune response: methotrexate, rituximab, and eculizumab.
- Thymectomy The thymus is thought to be located in the upper middle chest between the lungs and is thought to play a role in the autoimmune response in MG. During a thymectomy, the gland is surgically removed. A randomized controlled trial showed that thymectomy was effective in reducing the dose of prednisone (an immunosuppressive drug) needed by a specific subset of people with MG.
- Methotrexate did not reduce the need for prednisone in a randomized controlled trial in people with MG with AchR antibodies.
- Rituximab According to the consensus report, it is helpful for people with MuSK MG, less so for people with AchR MG.
- Eculizumab is a new drug with a novel mechanism of action to improve physical function in people with MG who have not responded to previous treatments. Immunization against meningococci (a group of bacteria that cause meningitis) is required before treatment. Eculizumab is given by injection into a vein once a week for five weeks and then every two weeks after this first period.
Many people with autoimmune MG need long-term immunosuppressive treatment to manage their disorder. The best treatment options are determined by monitoring disease progression and response to treatments over time.
Treatment for MG is complex. Your neurology team will consider various factors, including age, gender, pregnancy, and breastfeeding, as well as other diseases (such as high blood pressure, diabetes, or liver disease). They also take into account the presence and type of MG antibodies, the type of MG (eye MG or generalized MG, which affects more than just the eyes), and your preferences and values.
As new treatment information becomes available, discuss possible treatment changes with your neurologist. They can help you ensure that the treatment decisions you have made are in line with your improvement goals and your personal values and preferences.