Myasthenia Gravis

Myasthenia gravis is an autoimmune neuromuscular disorder. Usually, the body's immune system makes antibodies to attack germs that invade the body. "Autoimmune" means that a person's immune system malfunctions and it creates antibodies that attack the person's own cells. In myasthenia gravis, the antibodies interfere with the transmission of nerve signals to the muscles. In other words, the muscles don't receive the signal from the nerves to move.

Who Is at Risk?

Myasthenia gravis is not inherited, and it is not contagious. It is not clear why people develop the disorder, although some researchers believe it could be from a genetic problem. In the United States, about 14 out of every 100,000 people develop myasthenia gravis, although researchers believe the numbers are probably higher since the disorder is often not diagnosed correctly. For women, the disorder usually starts in their 20s and 30s; for men, usually after age 50.

Symptoms

Often, a person will have specific muscle weakness and not overall tiredness or fatigue. The muscles most commonly affected are:

• drooping eyelids (first symptom in 2/3 of all patients)
• mouth weakness, leading to trouble chewing, swallowing, or talking (first symptom in 1/6 of patients)
• arm or leg weakness (less common as a first symptom)

One clue is that the weakness varies throughout the day, generally being mild when the person wakes up but getting worse as the day goes on, especially if the person is using the affected muscles a lot. This weakness is different than, for example, the tiredness someone might feel in his legs after standing or working all day. "Weakness" means not being able to move, or only barely being able to move, a particular muscle.

Other factors that make the muscle weakness worse are being emotionally upset, being sick (especially viral respiratory infections), thyroid problems, increased body temperature, menstruation and pregnancy.

Diagnosis

If a person has symptoms that suggest he might have myasthenia gravis, there are tests that can be done to confirm it. The most specific test is to check the blood for the presence of abnormal antibodies using the acetylcholine receptor antibody test. Presence of the antibodies confirms the diagnosis.

Another reliable test is the edrophonium chloride test (Tensilon test). This chemical is injected into a vein, and if muscle strength improves after it is given, it is strong support for the diagnosis. However, sometimes one or both of these tests are negative or not clear in someone who seems as if he has myasthenia gravis.

Treatment

Common treatments for myasthenia gravis include:

• medications such as Mestinon (pyridostigmine bromide) and Prostigmin (neostigmine bromide)
• corticosteroid medications such as prednisone
• medications that suppress the immune system, such as Imuran (azathioprine) and cyclosporine
• removal of the thymus gland (thymectomy), the main gland in the immune system
• plasma exchange (plasmapheresis), in which the person's blood plasma containing the abnormal antibodies is removed and fresh plasma is put back

The Long-Term Outlook

People with myasthenia gravis can in most cases lead full lives. Sometimes the muscle weakness resolves to the point of not being a problem (called spontaneous remission). For some people, the weakness is only in the eyelids. For others, the weakness progresses to a point and stays at that level. Rarely, and usually in the first two years of the disorder, the weakness might extend to the muscles that control breathing, and the person will have to be hospitalized. There is no cure for myasthenia gravis, but the treatments are usually effective in minimizing its problems.

Researchers looking at a cure for the disorder are focusing on correcting the problem in the immune system that creates the abnormal antibodies. Researchers are also examining the whole chain of events in the body that occurs with the release of the antibodies, to see if they can interrupt the process along the way and stop antibodies from causing problems.

_Sources:

"What is Myasthenia Gravis?." About Myasthenia Gravis. 15 Feb 2007. Myasthenia Gravis Foundation of America. 17 Jun 2008