Myasthenia gravis

Myasthenia gravis (mi-uhs-THEE-ne-uh GRA-vis) is characterized by weakness and rapid fatigue of any of the muscles under your voluntary control. The cause of myasthenia gravis is a breakdown in the normal communication between nerves and muscles.
There is no cure for myasthenia gravis, but treatment can help relieve signs and symptoms —
such as are
weakness of arm or leg muscles,
double vision,
drooping eyelids,
difficulties in
 speech,
 chewing,
 swallowing
 and breathing.
While myasthenia gravis can affect people of any age, it's more common in women younger than 40 and in men older than 60.


Symptoms

Muscle weakness caused by myasthenia gravis worsens as the affected muscle is used repeatedly. Since symptoms typically improve with rest, your muscle weakness may come and go. However, the symptoms of myasthenia gravis tend to progress over time, usually reaching their worst within a few years after the onset of the disease.
Although myasthenia gravis can affect any of the muscles that you control voluntarily, certain muscle groups are more commonly affected than others.


Eye muscles
In more than half the people who develop myasthenia gravis, their first signs and symptoms involve eye problems, such as:
• Drooping of one or both eyelids (ptosis)
• Double vision (diplopia), which may be horizontal or vertical
Face and throat muscles
In about 15 percent of people with myasthenia gravis, the first symptoms involve face and throat muscles, which can cause difficulties with:
• Altered speaking. Your speech may be very soft or may sound nasal, depending upon which muscles have been affected.
• Difficulty swallowing. You may choke very easily, which makes it difficult to eat, drink or take pills. In some cases, liquids you're trying to swallow may come out your nose.
• Problems chewing. The muscles used for chewing may wear out halfway through a meal, particularly if you've been eating something hard to chew, such as steak.
• Limited facial expressions. Family members may note that you've "lost your smile" if the muscles that control your facial expressions are affected.


Neck and limb muscles
Myasthenia gravis can cause weakness in your neck, arms and legs, but this usually happens in conjunction with muscle weakness in other parts of your body — such as your eyes, face or throat. The disorder usually affects arms more often than legs. However, if it affects your legs, you may waddle when you walk. If your neck is weak, it may be hard to hold your head erect.


Causes

Your nerves communicate with your muscles by releasing chemicals, called neurotransmitters, which fit precisely into receptor sites on the muscle cells. In myasthenia gravis, your immune system produces antibodies that block or destroy many of your muscles' receptor sites for a neurotransmitter called acetylcholine. With fewer receptor sites available, your muscles receive fewer nerve signals, resulting in weakness.
It's believed that the thymus gland — a part of your immune system situated in the upper chest beneath the breastbone — may trigger or maintain the production of these antibodies. Large in infancy, the thymus is small in healthy adults. But, in some adults with myasthenia gravis, the thymus is abnormally large. Some people also have tumors of the thymus. Usually, thymus gland tumors are noncancerous.
Factors that can worsen myasthenia gravis
• Fatigue
• Illness
• Stress
• Extreme heat
• Some medications — such as beta blockers, calcium channel blockers, quinine and some antibiotics