Myasthenia Gravis

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Overview

Source: In partnership with Genetic and Rare Diseases Information Center, funded by the National Center for Advancing Translational Sciences, and the National Human Genome Research Institute https://rarediseases.info.nih.gov/gard.

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Myasthenia gravis

overview Question

What is myasthenia gravis?

Myasthenia gravis is a chronic autoimmune neuromuscular disease. It is characterized by varying degrees of weakness of the skeletal muscles of the body. Common symptoms include weakness of the muscles that control the eye and eyelid; facial expressions; chewing; talking; and swallowing. Weakness tends to increase during periods of activity and improves after periods of rest. The exact cause of myasthenia gravis is unknown. Some cases have been linked to tumors in the thymus gland. Researchers believe that variations in certain genes may increase a person's risk to develop this condition, but it is likely that other factors also play a role. There is no cure for myasthenia gravis, but lifestyle changes and some medicines may allow for periods without symptoms (remission).

Date Modified: 2016-06-07T00:00:00

basic Questions

What are the signs and symptoms of myasthenia gravis?

Myasthenia gravis can affect any voluntary muscle. Voluntary muscles are the muscles that we directly control to make our body do things like walk, run, write, throw, lift, smile, and chew. In myasthenia gravis the most commonly affected muscles are the muscles that control eye and eyelid movement, facial expression, and swallowing. The degree of muscle weakness varies from person to person. People with more severe disease may have many muscles affected, including the muscles that control breathing. People with mild disease may have only one muscle group involved, such as the eye muscles.

In general, signs and symptoms of myasthenia gravis may include a drooping of one or both eyelids (ptosis); blurred or double vision (diplopia); unstable or waddling gait; weakness in the arms, hands, fingers, legs, and neck; a change in facial expression; difficulty in swallowing and shortness of breath; and impaired speech (dysarthria).

People can develop myasthenia gravis at any age. For unknown reasons, it is most commonly diagnosed in women younger than age 40 and men older than age 60. It is uncommon in children, but some infants born to women with myasthenia gravis have signs and symptoms of the condition for the first few days or weeks of life. This temporary occurrence of symptoms is called transient neonatal myasthenia gravis.

Date Modified: 2016-06-07T00:00:00

What causes myasthenia gravis?

The exact cause of myasthenia gravis is unknown, but it is likely that many factors contribute to the risk of developing this disorder.

Myasthenia gravis is a type of autoimmune disorder. Autoimmune disorders occur when the immune system mistakenly attacks healthy tissue. In myasthenia gravis, the body produces antibodies that block the muscle cells that receive messages (neurotransmitters) from the nerve cells.

Normally when impulses travel down the nerve, the nerve endings release a neurotransmitter substance called acetylcholine. Acetylcholine travels from the neuromuscular junction - the place where nerve cells connect with the muscles they control -  and binds to acetylcholine receptors which are activated and generate a muscle contraction. In myasthenia gravis, antibodies block, alter, or destroy the receptors for acetylcholine at the neuromuscular junction,which prevents the muscle contraction from occurring. These antibodies are produced by the body's own immune system. 

In some cases, myasthenia gravis it is linked to tumors or other abnormalities of the thymus (a gland the plays an important role in the immune system). Researchers also believe that variations in particular unidentified genes may increase the risk to develop myasthenia gravis. Ultimately, many factors likely contribute to the risk of developing this complex disorder.

Date Modified: 2016-02-09T00:00:00

Is myasthenia gravis inherited?

Myasthenia gravis is not directly inherited, nor is it contagious. However, a genetic predisposition to autoimmune disease can run in families. Occasionally, myasthenia gravis may occur in more than one member of the same family.

Date Modified: 2016-06-07T00:00:00

How rare is myasthenia gravis?

In the US, the estimated annual incidence of myasthenia gravis (number of newly diagnosed cases) has been reported as 1 in 500,000 people. To our knowledge, estimates of prevalence (total number of cases that exist at a given time) in the US range considerably from 1 in 2,500 to 1 in 200,000 people. The prevalence appears to have risen over the past 2 decades, mostly due to earlier diagnosis and increased lifespan of affected people.

While myasthenia gravis can occur at any age, the female incidence is highest in the third decade of life, and the male incidence is highest in the sixth or seventh decade. The average age of onset is 28 years in females and 42 years in males.

Date Modified: 2016-03-09T12:03:00

Presentation(s)

Autoimmunity

Diplopia

Dysarthria

Dysphagia

Facial palsy

Fatigable weakness

Limb muscle weakness

Nasal speech

Proximal muscle weakness

Ptosis

Thymoma