Myasthenia gravis (MG) is a disorder that affects the interaction between nerves and muscles. Patients with MG experience muscle weakness, rapid fatigue and can sometimes experience difficulty breathing. MG can be a serious condition. However, many affected patients are able to live normal lives with treatment and can expect a normal life span.

MG is an uncommon condition. According to the Myasthenia Gravis Foundation of America, it occurs in approximately 20 out of every 100,000 people in the United States. The condition is slightly more prevalent in women than in men. Symptoms and signs often develop at different ages based on gender. MG may occur at any age. In women, it typically presents before the age of 40 and in men it often appears after age 60.

The symptoms of MG result from the body’s immune system attacking the communication between nerves and muscles. Normally, neurons (nerve cells) release chemicals called neurotransmitters that signal muscles to contract. In patients with MG, the immune system produces antibodies (proteins that ward off substances considered "foreign" to the body) that work against these neurotransmitters or their receptors in the muscles. This prevents or limits the muscle contraction and patients feel weak with motion or exertion.

MG can affect any muscle in the body, but most often affects muscles that control voluntary movement and breathing. The eyes are frequently affected and patients may experience drooping eyelids, blurry vision or double vision. When the muscles of the head and neck are weakened, patients may have difficulty talking, chewing or swallowing. When muscles in the extremities are affected, patients may feel weakness in the arms, hands, fingers or legs.

The symptoms of MG often worsen after activity and improve with rest. They can also become more severe due to fatigue, illness or stress. These changes in symptoms help differentiate MG from other neuromuscular diseases such as muscular dystrophy and amyotrophic lateral sclerosis (Lou Gehrig’s disease) in which weakness does not improve after rest.

A physician may suspect a patient has MG based on the presenting symptoms, but will use a variety of tests to confirm the diagnosis. These are likely to include blood tests, nerve conduction velocity studies, electromyograms and computed axial tomography scans.

MG may be treated to limit the frequency and severity of symptoms. Long-term treatment may be accomplished with medications. Another alternative is thymectomy - surgery to remove the thymus gland that is involved in the immune response and may be abnormally active and enlarged in patients with MG. With thymectomy, the disease sometimes regresses to the point that patients require no further medication. Other treatments, such as plasmapheresis and high dose intravenous immune globulin, may provide temporary relief from severe periods of active symptoms.