How is treatment for myasthenia gravis evolving?

Myasthenia gravis (MG) – a medical term that translates to “severe muscle weakness” – is a rare neuromuscular disease. It is estimated that 30,000 to 60,000 people in the United States suffer from this disorder, which affects people of all ages, genders and ethnicities. Recently updated consensus guidelines have enriched our knowledge of the different forms of myasthenia gravis and improved treatment approaches.

What are the symptoms of myasthenia gravis?

Myasthenia gravis affects the transmission of signals from nerves to muscles at a site called the neuromuscular junction (NMJ), where nerves come into contact with muscles. This causes temporary weakness in the muscles during use. When the affected muscle or muscle group is at rest, it regains strength.

Throughout the day, your body uses many muscle groups repeatedly; this is true even if you are not particularly active. Since myasthenia gravis is characterized by use-related weakness in certain muscle groups, repeated activity of the affected muscle worsens the weakness. The weakness improves with rest, only to recur as activity resumes.

The muscle groups 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 as the day goes on, their eyelids sag. After a nap, their eyes are wide open. They can start to see very well when they are driving, but when they are driving they develop double vision. They can’t eat a whole bagel because their jaw gets tired after a while, although they can eat pasta without a problem. Their arms get tired halfway through drying their hair and they have to stop, lower their arms for a while, then continue.

What are the causes of myasthenia gravis?

Several disorders and even certain drugs can affect the neuromuscular junction. I will focus here on a form of myasthenia gravis called autoimmune MG. If you have autoimmune MG, your immune system makes antibodies that inappropriately attack certain proteins at the junction. One of these proteins is the acetylcholine receptor (AchR), located on the muscle membrane at the junction.

This particular protein binds to a chemical messenger called acetylcholine (Ach). Ach is released by the nerve ending when an electrical signal reaches it, causing a muscle to contract. But AchR antibodies destroy and reduce the number of AchR, so the transmission of impulses from the nerve to the muscle is impaired, resulting in muscle weakness.

Antibodies can also be raised against other important proteins at the neuromuscular junction that would normally help maintain AchR proteins, causing the same end result. Two of these proteins that can be targeted by antibodies are specific muscle kinase (MuSK) and lipoprotein-bound protein 4 (LRP-4).

How is myasthenia gravis treated?

Treatment is primarily aimed at improving symptoms. The most commonly used drug is pyridostigmine. Pyridostigmine prolongs the time Ach remains in the neuromuscular junction, thus giving it a better chance to bind to the reduced number of AchR receptors.

Additionally, 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) assembled an international working group of neuromuscular specialists to develop treatment advice. This group updated these guidelines in 2020, adding new recommendations for a surgery called thymectomy; treat ocular MG (MG confined to the muscles around the eyes); and the use of three drugs to treat an abnormal immune response: methotrexate, rituximab, and eculizumab.

  • Thymectomy Located in the middle of the chest, between the lungs, the thymus gland is thought to play a role in the autoimmune response to MG. During a thymectomy, the gland is surgically removed. A randomized controlled trial has shown that thymectomy is effective in reducing the dose of prednisone (an immunosuppressive drug) needed by a specific subgroup 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 is useful for people with MuSK MG, according to the consensus report, but less useful for those with AchR MG.
  • Eculizumab is a new medicine with a new mechanism of action that improves physical function in people with MG who have not responded to previous treatments. Vaccination against meningococcus (a group of bacteria that causes meningitis) is necessary before treatment. Eculizumab is given by injection into a vein once a week for five weeks and then every two weeks after this initial period.

Many people with autoimmune MG need long-term immunosuppressive therapy to help them manage their disorder. The best treatment options are decided by monitoring the course of the disease and the response to treatments over time.

The treatment of MG is complex. Your neurology team will consider several factors, including age, gender, pregnancy and breastfeeding, and other conditions (such as high blood pressure, diabetes, or liver disease). They will also take into account the presence and type of MG antibodies, the type of MG you are having (ocular MG or generalized MG, which affects more than the eyes alone), and your preferences and values.

As new treatment information becomes available, discuss possible treatment changes with your neurologist, who can help you make sure that the treatment choices you make match your goals for improvement, as well as your goals. personal values ​​and preferences.

The post How is the treatment of myasthenia gravis progressing? first appeared on the Harvard Health Blog.

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Jothi Venkat

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