The term “Myasthenia Gravis” comes from Greek and Latin words. In English, this translates to “grave muscle weakness.
MG is a disease that is caused by your body’s own immune system attacking itself. People with MG typically experience many symptoms, which can include muscle weakness in the arms, legs, or neck, double vision, drooping eyelids, difficulty with speech, chewing, swallowing, or breathing as well as mental and physical fatigue.
MG is not inherited or contagious.
Thymus involvement: Although the cause is not known, about 75% of people living with MG have a problem with their thymus gland but the role of the thymus in MG is not currently understood. The thymus is a small organ that sits behind the breast bone which produces cells that are essential for the body’s immune system to work properly.
Autoantibodies: In healthy individuals, the immune system produces antibodies to protect the body from infections and diseases. However, in the case of MG, this process malfunctions and leads to the production of antibodies that block receptors in the muscles. Antibodies that target the body’s own tissues are called autoantibodies.
When muscle receptors are blocked, as they are by autoantibodies in MG, the muscles themselves receive fewer nerve signals and are unable to contract properly, which leads to muscle weakness and fatigue.
Normally, nerves signal our muscles to contract using a chemical messenger molecule called acetylcholine, which binds to the acetylcholine receptor (AchR). In the most common form of MG, autoantibodies prevent the binding of acetylcholine to AchR, which means the muscles are unable to contract properly, resulting in muscle weakness.
In MG, when autoantibodies target different muscle groups in the body, that is when the symptoms of the disease start to appear. So, for example, receptors in muscles of the arms and legs when targeted cause limb weakening, receptors in muscles of the mouth, throat, and neck when targeted cause difficulty in speaking, chewing or swallowing.
Because of its rarity and different symptoms, many patients with MG may struggle to receive an accurate diagnosis for months or even years. MG disease can affect anyone, but it is more commonly diagnosed in women aged under 40 years and in men aged over 60.
Tests that can diagnose MG include physical and neurological examinations, tests that stimulate the nervous system and measure muscle response, and blood tests:
In some cases, an injection of a medicine called edrophonium chloride is given. Edrophonium chloride is a drug that temporarily inhibits the breakdown of acetylcholine, a neurotransmitter that is essential for muscle contraction. If a sudden but temporary improvement in muscle strength is seen after the injection, an MG diagnosis is likely.