Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune disease which results in progressive weakness and tiring of the muscles that people can consciously control.  Abnormal antibodies produced by the immune system disrupt communication from the nerves to the muscles.

MG can affect any muscle, but the muscles that control eye and eyelid movement, facial expression, and swallowing are most often affected. Common first symptoms are weakness of the eye muscles, difficulty swallowing, talking, and breathing. Different people have different levels of muscle weakness. The onset of the disorder may be sudden.

Normally, the body releases a molecule called a neurotransmitters (acetylcholine) which binds to the muscle tissue at the nerve-muscle junction, causing the muscle to contract. In MG, the body's own immune system makes antibodies that block the binding of acetylcholine to the muscle.  The thymus gland, part of the immune system, is abnormal in most MG cases.

Most people with MG have good results from treatment. In some people, MG may go into remission for a while and muscle weakness may go away completely. In rare cases, people go into remission or improve without treatment. Treatment for MG may include cholinesterase inhibitors, such as pyridostigmine. These drugs help improve nerve signals to muscles and increase muscle strength. Immunosuppressive drugs frequently are used to suppress the production of abnormal antibodies. Surgical removal of the thymus gland may improve symptoms.

MG can affect any muscle, but the muscles that control eye and eyelid movement, facial expression, and swallowing are most often affected. In some people, the first symptom is weakness of the eye muscles. In others, having a hard time swallowing, talking, and breathing can be the first signs. Different people have different levels of muscle weakness.

Symptoms may include:

• Drooping of one or both eyelids
• Blurred or double vision
• Problems walking
• Weakness in arms, hands, fingers, legs, and neck
• Change in facial expression
• Having a hard time swallowing
• Trouble talking
• Shortness of breath (feeling like you can’t get enough air)

The onset of the disorder may be sudden. And the symptoms often are not immediately recognized as MG.

Some drugs can trigger or worsen MG symptoms.

With MG, normal communication between the nerve and muscle is stopped at the place where nerve endings connect with the muscles they control — the nerve-muscle junction. Normally, the nerve endings release a substance called acetylcholine, which binds to the muscle tissue at the nerve-muscle junction, causing the muscle to contract (move). In someone with MG, the body's own immune system makes antibodies that block the binding of acetylcholine to the muscle.

The thymus gland, part of the immune system, is abnormal in most MG cases. Some people with MG have benign tumors of the thymus gland called thymomas. Doctors do not fully understand the relationship between the thymus gland and MG.

MG is hard to diagnose because weakness is a common symptom of many disorders and it often starts very gradually and can be mild at first.

Your doctor will ask you about your symptoms, take a medical history, and perform a physical exam. If your doctor thinks you may have MG, she or he may run some tests:

• Antibody blood tests. Blood tests can detect the presence of high levels of abnormal antibodies that prevent normal nerve-to-muscle transmission. Most people with MG have abnormally high levels of acetylcholine receptor antibodies. But some people with MG test negative for these antibodies. Recently, another type of antibody, called MuSK antibodies, has been found in some MG patients who test negative for acetylcholine receptor antibodies. For these patients, a blood test that detects MuSK antibodies can be a useful diagnostic tool. Just how MuSK antibodies alter or damage nerve-muscle transmission isn't clear. But patients who test positive for MuSK antibodies often have symptoms involving face muscles, swallowing, speech, and breathing. Abnormal antibodies may not be found if only eye muscles are affected by MG.
• Edrophonium test. When this drug is injected into someone with MG, his or her normally weak eye muscles will get stronger for a few minutes.
• Nerve conduction test/repetitive stimulation. With this test, a nerve linked with a specific muscle is stimulated to see if the muscle action is weakened.
• Single fiber electromyography (EMG). In this test, single muscle fibers are stimulated by electrical impulses. Muscle fibers of people with MG do not respond to repeated electrical stimulation as well as muscles that function normally. With this test, the EMG can detect problems with nerve-to-muscle transmission.
• Computed tomography (CT) or magnetic resonance imaging (MRI). This test can show if you have an abnormal thymus gland or a thymus gland tumor.

To help ease fatigue:

• Get plenty of rest.
• Budget your energy.
• Rest your eyes or lie down briefly a few times a day.
• Work with your neurologist.
• Work with your doctor to limit medication side effects and keep your general health good.
• Eat healthy foods from all the major food groups.

There are several therapies that can help strengthen the muscles of someone with MG. Most people with MG have good results from treatment. In some people, MG may go into remission for a while and muscle weakness may go away completely. In rare cases, people go into remission or improve without treatment.

Treatment for MG may include:

• Medications. Drugs used include cholinesterase inhibitors, such as pyridostigmine. These drugs help improve nerve signals to muscles and increase muscle strength. Immunosuppressive drugs frequently are used to suppress the production of abnormal antibodies. They must be used with careful medical supervision because they can cause major side effects.
• Thymectomy. This is the surgical removal of the thymus gland, which is abnormal in most persons with MG. This surgery is done for people with MG who have tumors, as well as for some who don't have tumors. The surgery improves symptoms in most MG patients who receive it.

Other therapies sometimes used to treat MG when weakness is very acute include:

• Plasmapheresis or plasma exchange. This procedure removes abnormal antibodies from the blood. This provides relief from MG symptoms in many patients for a few weeks.
• High-dose intravenous immune globulin. This treatment keeps the immune system from damaging the nerve-muscle junction for a short time. This provides relief from MG symptoms in many patients for weeks to months.

Your doctor will decide which treatment is best for you depending on the severity of the weakness, which muscles are affected, and your age and other medical problems. With treatment, many people with MG can expect to lead normal lives.

A myasthenic crisis occurs when weakness affects the muscles that control breathing. This can create a medical emergency requiring either a respirator to help the person breathe or measures to prevent a person from taking too much air into their lungs. Weak respiratory muscles, infection, fever, or a bad reaction to medication can also trigger a crisis. The treatments described above — in particular, intravenous immune globulin and plasma exchange — can reverse the severe weakness of a myasthenic crisis.