Myasthenia gravis is an autoimmune disease that affects the transmission of signals from nerves to muscles. The name myasthenia gravis comes from Greek and Latin words meaning "grave muscle weakness." Today, however, most cases of MG are not as "grave" as the name implies. In fact, most people with MG can expect to live normal or nearly normal lives.
The hallmark of MG is muscle weakness that increases during activity and improves after rest. MG often involves muscles that control eye and eyelid movement, facial expression, chewing, talking, and swallowing. The muscles that control breathing and neck and limb movements may also be affected.
The thymus gland, part of the immune system, is abnormal in most MG cases. Some people with MG have benign (noncancerous) tumors of the thymus gland called thymomas.
Some drugs can trigger or worsen MG symptoms.
Estimates of the number of people affected by MG vary, ranging from five to 14 people per 100,000.
MG occurs in all ethnic groups and both genders. It most commonly affects young adult women (under 40) and older men (over 60), but it can occur at any age. Children sometimes develop MG.
MG is not directly inherited nor is it contagious. Sometimes the disease may occur in more than one member of the same family. If a woman with MG becomes pregnant, sometimes the baby acquires antibodies from the mother and has MG symptoms for a few weeks or months after birth. This is called neonatal myasthenia, and the symptoms can be treated.
In rare cases, myasthenia is caused by a defective gene and appears in infants born to non-myasthenic mothers. This type is called congenital myasthenia.
MG is caused by a defect in the transmission of nerve signals to muscles. Normally, nerve endings release a substance called acetylcholine that binds or attaches to receptors on the muscle. This leads to muscle contractions. In MG, the body's own immune system produces antibodies that block this transmission.
The thymus gland, found in the upper chest area beneath the breastbone, is a part of the body's normal immune system. In most adults with MG, the thymus gland is abnormal. Some people with MG develop thymomas or tumors on the thymus gland. Generally thymomas are benign, but they can become malignant (cancerous). The relationship between the thymus gland and MG is not yet fully understood.
A myasthenic crisis occurs when weakness affects the muscles that control breathing. This can create a medical emergency requiring a respirator to help the person breathe or measures to prevent a person from taking in, or aspirating, too much air into their lungs. In individuals whose respiratory muscles are weak, infection, fever, a reaction to medication, or emotional stress can trigger a crisis.
You can follow a few simple steps to help cope with the condition in your daily life. Plenty of rest and a well balanced, potassium-rich diet can help ease fatigue. Good sources of potassium include oranges, orange juice, and bananas. It is important to avoid overexertion, and if necessary, to rest the eyes or to lie down briefly a few times a day.
Since it is an autoimmune disease, it may occur in combination with other autoimmune conditions such as rheumatoid arthritis, Sjorgrens syndrome, lupus, pernicious anemia, orautoimmune thyroiditis.