Myasthenia Gravis (MG)
What is myasthenia gravis?
Myasthenia gravis (MG) is an autoimmune disease, meaning the body’s immune system mistakenly attacks its own parts. MG affects the communication between nerves and muscles (the neuromuscular junction).
People with MG lose the ability to control muscles voluntarily. They experience muscle weakness and fatigue of various severity. They may not be able to move muscles in the eyes, face, neck and limbs. MG is a lifelong neuromuscular disease. There isn’t a cure, but treatments can help and some patients may achieve remission.
How common is myasthenia gravis?
MG affects about 20 out of every 100,000 people. Experts estimate that 36,000 to 60,000 Americans have this neuromuscular disease. The actual number of people affected may be higher, as some people with mild cases may not know they have the disease.
Who might get myasthenia gravis?
MG mostly affects women aged 20 to 40 and men aged 50 to 80. About one in 10 cases of MG occur in teenagers (juvenile MG). The illness can affect people of all ages but is rare in children.
These factors increase risk:
- History of other autoimmune diseases, such as rheumatoid arthritis and lupus.
- Medications for malaria, heart arrhythmias and cancer.
- Surgical procedures.
- Thyroid disease.
What are the types of myasthenia gravis?
Autoimmune MG is the most common form of this neuromuscular disease. Autoimmune MG may be:
- Ocular: The muscles that move the eyes and eyelids weaken. Your eyelids may droop, or you may not be able to keep your eyes open. Some people have double vision. Eye weakness is often the first sign of MG. Nearly half of people with ocular MG evolve into the generalized form within two years of the first symptom.
- Generalized: Muscle weakness affects the eye and other body parts such as the face, neck, arms, legs and throat. You may find it difficult to speak or swallow, lift your arms over your head, stand up from a seated position, walk long distances and climb stairs.
How does myasthenia gravis affect pregnancy?
In rare instances, pregnancy brings on MG symptoms for the first time. If you already have MG, symptoms may worsen during the first trimester or immediately after childbirth. In some patients, MG symptoms improve during pregnancy.
Certain MG treatments are not safe during pregnancy or breastfeeding. Your healthcare provider can guide you through this time, ensuring a healthy pregnancy.
Is myasthenia gravis inherited?
In general, autoimmune MG isn’t inherited. It’s rare for more than one member of the same family to receive a diagnosis of autoimmune MG. The non-autoimmune form of MG (also called congenital myasthenic syndrome) can affect more than one member of the same family.
A pregnant woman cannot pass MG to her infant. However, about one in 10 babies born to women with MG develop a temporary condition called neonatal myasthenia. These infants may have weak cries or sucking reflexes at birth. These symptoms go away in a few weeks. This condition doesn’t increase a child’s risk of developing MG in the future.
Symptoms and Causes
What causes myasthenia gravis?
MG is an autoimmune disease. For unknown reasons, the body’s immune system attacks itself.
In someone with a healthy immune system, nerves and muscles communicate a bit like a tiny baseball game:
- Nerves (the pitcher) send signals to muscles (the catcher) across a synapse (connection) called the neuromuscular junction. To communicate, nerves release a molecule called acetylcholine (the baseball).
- Muscles have sites called acetylcholine receptors (the catcher’s glove). The acetylcholine binds to the receptors in the muscle tissue, like a ball landing in a glove.
- When the acetylcholine binds to the receptor, it triggers the muscle fiber to contract.
In a healthy person, nerves signal muscles work effortlessly, like one ballplayer catching a ball and throwing it to a teammate.
But people with MG have antibodies that destroy the receptor sites, blocking nerve-muscle communication. The “catcher” can’t catch the ball, and communication becomes sluggish or doesn’t work at all.
What is the connection between thymus gland problems and MG?
Many people with MG have thymus gland conditions that may bring on MG. The thymus is a small organ in the upper chest that is part of the lymphatic system. It makes white blood cells that fight infections. Two-thirds of young people with MG have overactive thymic cells (thymic hyperplasia). About one in 10 people with MG have thymus gland tumors called thymomas, which may be benign (not cancer) or cancerous.
What are the symptoms of myasthenia gravis?
Initial symptoms of MG often come on suddenly. The neuromuscular disease causes your muscles to get weaker when you’re active. Muscle strength returns when you rest.
The intensity of muscle weakness often changes from day to day. Most people feel strongest at the start of the day and weakest at the end of the day.
Symptoms of MG include:
- Double vision.
- Drooping eyelids (ptosis).
- Difficulty speaking, chewing or swallowing.
- Difficulty moving their neck up or holding up their head.
- Limb weakness.
- Trouble walking.
Diagnosis and Tests
How is myasthenia gravis diagnosed?
Your healthcare provider will perform a physical exam and assess your symptoms. You may undergo these tests:
- Ice pack test: If you have severely drooping eyelids, your provider may place ice packs on your eyes or have you rest with your eyes shut in a dark room for a few minutes. If the drooping improves after the ice application or rest, you may have MG.
- Antibody tests: About 85% of people with MG have unusually high levels of acetylcholine receptor antibodies in their blood. Approximately 6% patients have muscle-specific kinase (MuSK) antibodies. Antibodies may not be detected in less than 10% of MG patients.
- Imaging scans: An MRI or CT scan can check for thymus gland problems like tumors.
- Electromyogram (EMG): An EMG measures the electrical activity of muscles and nerves. This test detects communication problems between nerves and muscles.
Management and Treatment
What are the complications of myasthenia gravis?
Up to one in five people with MG experience a myasthenic crisis or severe respiratory muscle weakness. They may need a respirator or other treatments to help them breathe. This is a life-threatening medical emergency. Weak muscles, infections, fevers and reactions to medications can cause a crisis.
How is myasthenia gravis treated?
Myasthenia gravis is a treatable disease and most patients will live a relatively normal life with treatment.
Treatments for MG focus on improving symptoms. Treatments include:
- Medications: Cholinesterase inhibitors (anticholinesterase) boost signals between nerves and muscles to improve muscle strength. Immunosuppressants, including corticosteroids, decrease inflammation and reduce your body’s production of abnormal antibodies.
- Monoclonal antibodies: You receive intravenous (IV) infusions of biologically engineered proteins. These proteins suppress an overactive immune system.
- IV immunoglobulin (IVIG): You receive IV infusions of donor antibodies over a period of two to five days. IVIG can treat myasthenia crisis as well as generalized MG.
- Plasma exchange (plasmapheresis): An IV line removes abnormal antibodies from your blood.
- Surgery: A thymectomy is surgery to remove the thymus gland. Even if tests don’t show a problem with your thymus gland, surgical removal sometimes improves symptoms.
How can I prevent myasthenia gravis?
Healthcare providers don’t know what triggers autoimmune diseases like MG. There isn’t anything you can do to prevent it.
How can I alleviate myasthenia gravis symptoms?
If you have MG, these steps can ease fatigue and boost muscle strength:
- Avoid going outside in the middle of a hot day. Apply cold compresses to your neck and forehead when you feel overheated. (Heat can make MG symptoms worse.)
- Exercise regularly to strengthen muscles, boost mood and have more energy.
- Get plenty of protein and carbohydrates in your diet for energy.
- Tackle your most exhausting tasks earlier in the day when you feel your best.
- Take naps or rest breaks throughout the day.
Outlook / Prognosis
What is the prognosis (outlook) for people who have myasthenia gravis?
With treatment, most people with MG lead full, active lives. Symptoms tend to reach their peak in severity within one to three years of initial diagnosis. For 15% of people with MG, the disease only affects the eyes and face (ocular MG).
When should I contact my healthcare provider?
You should call your healthcare provider if you experience:
- Blurred or double vision.
- Difficulty walking, talking or eating.
- Extreme muscle fatigue or weakness.
- Shortness of breath or difficulty breathing.
What questions should I ask my healthcare provider?
You may want to ask your healthcare provider:
- Why did I get MG?
- What is the best treatment for me?
- What are the treatment side effects?
- What lifestyle changes should I make?
- Should I look out for signs of complications?
A note from Cleveland Clinic
It’s challenging to live with a chronic illness like MG. Although there isn’t a cure, most people with MG lead productive, active lives. Severe disabilities from MG are extremely rare. Treatments and lifestyle changes can ease symptoms. Your healthcare provider can suggest ways to manage symptoms so you can continue to enjoy life.