Myasthenia gravis is a relatively rare neuromuscular disease in which the voluntary muscles easily become tired and weak because there is a problem with how the nerves stimulate the contraction of muscles. It is an autoimmune disorder.
"Myasthenia gravis" literally means "grave muscle weakness," but many cases are mild, and life expectancy is normal.
The muscles around the eyes tend to be affected first, causing the eyelids to droop. Patients may experience double vision, weakness in the arms and legs, and difficulties chewing, swallowing, speaking, and breathing. Involuntary muscles, such as the heart muscles, are not affected.
Symptoms often worsen with physical activity and improve after resting or a good night's sleep. There is no cure, but treatment can relieve and even remove symptoms.
The condition affects 14 to 20 people in every 100,000 in the United States, or between 36,000 and 60,000 people. It can happen at any age, but it is more likely to affect women before the age of 40 years, and men after the age of 60 years.
There is no cure for myasthenia gravis, but treatment with immunosuppressants or cholinesterase inhibitors can help control symptoms.
Many patients find that with treatment, and adequate sleep and rest, they can carry on with their normal routine.
- Cholinesterase inhibitors: These improve communication between nerves and muscles, and are effective in patients with mild symptoms of MG.
- Steroids, such as prednisolone, or immunosuppressants, such as azathioprine, may alter the body's immune system so that it produces fewer of the antibodies that cause MG.
It usually takes about 4 weeks for steroids to take effect. Azathioprine may take from 3 to 6 months, but it brings about a significant reduction or complete removal of symptoms.
In the case of a tumor, the thymus gland may be surgically removed in a thymectomy.
For patients with severe or life-threatening symptoms, plasmapheresis and immunoglobulin therapy can be administered in the hospital.
Plasmapheresis involves depleting the body of blood plasma without depleting the body of its blood cells, in order to remove the unwanted antibodies.
Intravenous immunoglobulin therapy involves injecting the patient with normal antibodies that change the way the immune system acts.
These treatments are effective, and they work quickly, but the benefits last only a few weeks, so this is a short-term treatment.
Symptoms of myasthenia gravis (MG) vary widely. In some people, only the eye muscles will be affected, while in others, it can impact many muscles, including those that control breathing.
The most prevalent symptom is fatigue.
Drooping in one or both eyelids, double vision, or both are an early sign in 2 out of every 3 patients. This can cause eyesight problems, and it is known as ocular myasthenia gravis.
In 1 in 6 patients, the throat and face muscles are the first to be affected.
They may have problems with:
- Speaking: Speech may become soft or nasal.
- Swallowing: The person may choke easily, and eating, drinking, and swallowing pills becomes harder. When the person drinks, liquid may come out of the nose.
- Chewing: The muscles used for chewing may weaken during a meal, especially if the food is hard or chewy, such as a steak.
- Facial expressions: A different or unusual smile may develop if certain facial muscles are affected.
Limb weakness is the first sign in 10 percent of patients. The arm and leg muscles may weaken, affecting activities such as lifting or walking.
When limb muscles are involved, other muscles also tend to be affected, such as the throat, eyes, or face.
Symptoms often become progressively worse during periods of activity, but they improve after resting.
What is a myasthenic crisis?
A myasthenic crisis is when the respiratory muscles become paralyzed.
The patient needs assisted ventilation to stay alive.
In a myasthenic crisis, the respiratory muscles become so weak that the patient cannot breathe properly.
This potentially life-threatening complication requires emergency treatment with mechanical breathing assistance. Plasmapheresis and immunoglobulin therapies can help.
People with one autoimmune disease are often susceptible to another. A person with MG may have a second autoimmune condition.
Other conditions include:
- Thyroid problems: These include overactive or underactive thyroid. The thyroid gland is a small gland in the front of the neck that secretes hormones that regulate metabolism.
- Lupus: This is an autoimmune disease that can lead to inflammation, swelling, and damage to joints, skin, kidneys, blood, the heart, and lungs.
- Rheumatoid arthritis: This is a chronic progressive and disabling condition that causes inflammation and pain in the joints, the tissue around the joints, and other organs in the human body.
Symptoms are generally more severe in the 2 to 3 years following diagnosis. However, people with MG can live a life without regular flareups as long as they stick to a regular treatment plan.
The condition spreads across the body in most people. However, 20 percent of people only see the effects of MG in the eyes.
Some people can experience a fatal case of MG, but these are rare. Most individuals with MG do not see a change in life expectancy.
MG is an autoimmune disorder. An autoimmune disorder develops when a person's immune system attacks their own body tissues.
The immune system is designed to find and destroy any unwanted invaders, such as bacteria, toxins, or viruses. In a person with an autoimmune disease, antibodies circulate in the blood and attack healthy cells and tissues by mistake.
In the case of MG, the antibodies block or destroy muscle receptor cells, resulting in fewer available muscle fibers. As a result, the muscles cannot contract properly, and they easily become tired and weak.
Exactly why this happens is unknown, but the thymus gland, located in the upper chest beneath the breastbone, appears to play a key role.
The thymus gland is large during infancy and continues to grow until puberty. After this, it gets smaller and eventually is replaced with fat. A significant number of adult patients with MG have an abnormally large thymus gland, and about 1 in 10 patients with MG have a benign tumor in the thymus gland.
Some medications or viruses may trigger the onset of MG. Drugs that may cause a worsening of symptoms in susceptible patients include beta blockers, calcium channel blockers, quinine, and some antibiotics.
Genetic factors may play a role.
Symptoms may also worsen with emotional or mental stress, illness, tiredness, or a high fever.
Neonatal myasthenia affects newborns if they acquire antibodies from a mother who has MG. The symptoms usually disappear in 2 to 3 months, and MG in infants and children is rare.
A physician may suspect MG if a patient has drooping eyelids but no problem feeling things, and if they are prone to muscle weakness that improves after rest.
Diagnosis can be difficult, however, because MG shares symptoms with other conditions. A neurologist may need to confirm the diagnosis.
People whose muscles are weak because of MG respond well when ice is applied to the affected area. Some doctors try this initially as they gather data to help them make a diagnosis.
A number of diagnostic tests will probably be ordered.
An edrophonium test involves injecting a substance into a vein and monitoring the reaction of the patient. The muscle weakness may be temporarily relieved.
Blood tests can identify certain antibodies.
Repetitive nerve stimulation involves attaching electrodes to the skin over the affected muscles and sending small electrical pulses through the electrodes to measure how well the nerves transmit the signal to the muscle. If a person has MG, the signals will get weaker as the muscle tires.
Single-fiber electromyography (EMG) measures the electrical activity that flows between the brain and the muscle. It involves inserting a very fine wire electrode through the skin, into the muscle.
A pulmonary function test, or spirometry, assesses how well the patient can breathe by measuring the maximum amount of air a person can expel from the lungs after breathing in deeply.
Performed regularly, this test can help to monitor any gradual worsening of muscular weakness in the lungs. This is especially important for patients with severe symptoms, to avoid severe breathing problems.
Muscle biopsy can be done to eliminate another muscular condition.
MG cannot be prevented. However, a person can take steps to stop a flare-up of symptoms or prevent them from developing complications.
These include practicing careful hygiene to avoid infections, and treating them promptly if they do occur.
It is also advisable to avoid extreme temperatures and overexertion. Effective stress management can also reduce the frequency and severity of symptoms.