Myasthenia gravis is a rare, chronic autoimmune neuromuscular disease that causes weakness of voluntary muscles. People of any age can be affected by this disease, but it is most commonly seen in women aged between 20 and 40. Men above the age of 50 are at higher risk of myasthenia gravis.
Causes of Myasthenia Gravis
Myasthenia gravis occurs due to interrupted communication between skeletal muscles and the nerves that control them. Normally, muscle movement depends on chemical signals from nerves. When these signals reach the nerve endings it triggers the release of a chemical called acetylcholine in the space called the neuromuscular junction where nerve cells connect with muscles. Acetylcholine binds with acetylcholine receptors causing the muscles to contract.
Myasthenia gravis is an autoimmune disorder. It occurs when the immune system produces antibodies to attack and destroy the acethylcholine receptors. Because of that, muscles do not receive nerve signals and cannot contract properly leading to muscle weakness. Myasthenia gravis can affect up to 80% of the receptors.
Exact cause of autoimmune disorder is unknown. However, the thymus gland, an organ of the immune system located above the heart, is believed to play an important role in development of myasthenia gravis. Precise role of the thymus is not understood but it has been observed that most people affected by myasthenia gravis have abnormally large thymus gland and some of them have tumors of the thymus.
Symptoms of Myasthenia Gravis
Myasthenia gravis affects muscles that are controlled voluntarily. The facial muscles are usually affected first especially the muscles controlling the eyelids. This causes eye problems such as eyelid drooping and double vision. Facial weakness can also cause difficulty chewing, swallowing, talking and making facial expressions.
The disease eventually spreads to other areas and may cause weakness of the neck resulting in drooping head. Limb muscles are usually also affected by myasthenia gravis leading to difficulty walking and lifting objects. Weakness of the chest wall muscles may result in breathing difficulty.
In general, muscle weakness caused by myasthenia gravis is aggravated by physical activity and improves with rest. With repetitive use, muscles become progressively weaker. Sometimes, severe weakness may occur suddenly (myasthenic crisis) due to an infection or stress.
Prevention of Myasthenia Gravis
It is impossible to prevent myasthenia gravis as the cause of disease is unexplained. However, individuals affected by it can prevent flare-ups by avoiding stress, strenuous activities and temperature extremes. People with myasthenia gravis should rest as much as possible and try to avoid exposure to infections such as flu and common cold.