Myasthenia gravis (my-us-THEE-nee-uh GRAY-vis) is a disease in which any of the muscles you can control voluntarily become weak and tired quickly. It happens when nerves and muscles can’t talk to each other as they should.
Myasthenia gravis has no cure, but treatment can help ease its signs and symptoms, such as muscle weakness in the arms or legs, double vision, drooping eyelids, and trouble speaking, chewing, swallowing, and breathing.
This disease can happen to people of any age, but it’s more likely to happen to women under 40 and men over 60.
Symptoms
When you use a muscle that is weak from myasthenia gravis, the weakness gets worse. Muscle weakness can come and go because most symptoms get better when you rest. But the symptoms usually get worse over time and are usually at their worst a few years after the disease starts.
Even though myasthenia gravis can affect any muscle you can control on your own, it affects some muscle groups more often than others.
Eye muscles
In more than half of people who develop myasthenia gravis, their first signs and symptoms involve eye problems, such as:
- Drooping of one or both eyelids (ptosis)
- Double vision (diplopia), which may be horizontal or vertical, improves or resolves when one eye is closed
Face and Throat Muscles
About 15% of people with myasthenia gravis experience the first symptoms in their face and throat muscles. These symptoms can include:
- Impair speaking. Depending on which muscles are affected, your speech might sound soft or nasal.
- Make it hard to swallow. You might find it hard to breathe, which makes it hard to eat, drink, or take pills. When you try to swallow liquids, sometimes they come out of your nose.
- affect how you chew. During the middle of a meal, your chewing muscles might get tired, especially if you’ve been eating something hard to chew, like steak.
- Change the way you look. Your smile might look like a snarl, for example.
Neck and limb Muscles
Myasthenia gravis can also make your arms, legs, and neck weak. If your legs are weak, it can change the way you walk. If the muscles in your neck are weak, it’s hard to hold your head up.
When to see a doctor
Talk to your doctor if you have difficulty:
- Breathing
- Seeing
- Swallowing
- Chewing
- Walking
- Using your arms or hands
- Holding up your head
Causes
Antibodies
At the nerve-muscle junction, your nerves send messages to your muscles by releasing chemicals called neurotransmitters. These chemicals fit exactly into receptor sites on the muscle cells.
In myasthenia gravis, your immune system makes antibodies that block or destroy many of the receptor sites in your muscles for acetylcholine, a neurotransmitter (as-uh-teel-KOH-leen). Since there are fewer receptor sites, your muscles get fewer nerve signals, which makes them weak.
Antibodies can also stop a protein from working. This protein is called muscle-specific receptor tyrosine kinase, or MuSK for short. This protein helps make the connection between nerves and muscles. Myasthenia gravis can happen if your body makes antibodies against this protein. Antibodies against a different protein called lipoprotein-related protein 4 (LRP4) can make this condition worse.
Researchers have found other antibodies, and the number of antibodies involved will likely grow over time. Some people with myasthenia gravis don’t have antibodies that stop acetylcholine, MuSK, or LRP4 from working. Seronegative myasthenia gravis, also called antibody-negative myasthenia gravis, is this type of disease. In general, researchers think that these types of myasthenia gravis are still caused by an autoimmune disease, but they can’t find the antibodies involved yet.
Thymus gland
The thymus gland is part of your immune system. It is in the upper chest, just below your breastbone. Researchers think that the thymus gland starts or keeps making antibodies that stop acetylcholine from working.
The thymus gland is big when a child is young, but it is small in healthy adults. Some adults with myasthenia gravis, though, have an abnormally large thymus gland. Some people who have myasthenia gravis also have thymus gland tumours (thymomas). Most of the time, thymomas are not cancerous, but they can turn into cancer.
Other causes
Mothers with myasthenia gravis rarely have babies who also have the disease (neonatal myasthenia gravis). If they get help right away, most children get better within two months of being born.
Some children are born with the congenital myasthenic syndrome, a rare form of myasthenia gravis that is passed down from parent to child.
Factors that can worsen myasthenia gravis
- Fatigue
- Illness or infection
- Surgery
- Stress
- Some medications — such as beta-blockers, quinidine gluconate, quinidine sulfate, quinine (Qualaquin), phenytoin, certain anaesthetics and some antibiotics
- Pregnancy
- Menstrual periods
Complications
Complications of myasthenia gravis are treatable, but some can be life-threatening.
Myasthenic crisis
A life-threatening condition called myasthenic crisis happens when the muscles that control breathing get too weak to work. We need emergency care and help with breathing from a machine. People can breathe on their own again with the help of medicines and therapies that filter the blood.
Thymus gland tumours
The thymus gland, which sits just below the breastbone and plays a role in immunological function, can become tumorous in certain persons with myasthenia gravis. Thymomas are a type of tumour that typically does not progress to malignancy (malignant).
Other disorders
People with myasthenia gravis are more likely to have the following conditions:
- Thyroid dysfunction, either underactive or hyperactive. Hormones secreted by the thyroid gland in the neck control metabolic rate. Thyroid underactivity has been linked to troubles with temperature regulation, excess body fat, and fatigue. Challenges with temperature regulation, rapid weight loss, and other symptoms are associated with an overactive thyroid.
- Inflammatory and auto-reactive disorders. Myasthenia gravis has been linked to an increased risk of developing autoimmune diseases like rheumatoid arthritis and lupus.
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