Summary
Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disease characterized by weakness of the skeletal muscles. 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 improve after periods of rest. The condition results from a defect in the transmission of nerve impulses to muscles, which is due to the presence of antibodies against acetylcholine.[1] The exact reason this occurs is not known. Some cases have been linked to tumors in the thymus gland.[2] Researchers believe that variations in certain genes may increase a person’s risk to develop MG, but other factors likely also play a role.[3] There is no cure for MG at this time, but treatment can significantly improve muscle weakness. Some cases may go into remission temporarily, and muscle weakness may disappear so that medications can be discontinued.[1][2]
Last updated: 4/3/2018
Symptoms
Myasthenia gravis (MG) causes muscle weakness and 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 MG, the most commonly affected muscles are the muscles that control eye and eyelid movement, facial expressions, 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.[1]
In general, signs and symptoms of MG may include:[1]
- Drooping of one or both eyelids (ptosis)
- Blurred or double vision (diplopia)
- Unstable or waddling gait (manner of walking)
- Weakness in the arms, hands, fingers, legs, and neck
- Change in facial expression
- Difficulty swallowing and shortness of breath
- Impaired speech (dysarthria)
People can develop MG 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 MG 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.[3]
Last updated: 4/3/2018
Cause
The exact cause of myasthenia gravis (MG) is unknown, but it is likely that a number of factors contribute to the risk of developing this disorder.[3]
MG is a type of autoimmune disorder. Autoimmune disorders occur when the immune system mistakenly attacks healthy tissue.[2] In MG, the body produces antibodies that block the muscle cells that receive messages (neurotransmitters) from the nerve cells.[2][1][3]
Normally when impulses travel down a 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 a muscle contraction from occurring. These antibodies are produced by the body’s own immune system.[1]
In some cases, MG is linked to tumors or other abnormalities of the thymus (a gland the plays an important role in the immune system).[2][1][3] Researchers also believe that variations in certain unidentified genes may increase the risk to develop MG.[3]
Last updated: 4/3/2018
Inheritance
Myasthenia gravis is not directly inherited, nor is it contagious.[4][5] However, a genetic predisposition to autoimmune disease can run in families.[5][3] Occasionally, myasthenia gravis may occur in more than one member of the same family.[4][3]
Last updated: 4/3/2018
Treatment
FDA-Approved Treatments
The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition.
- Eculizumab (Brand name: Soliris) – Manufactured by Alexion Pharmaceuticals, Inc.
FDA-approved indication: For the treatment of adult patients with generalized Myasthenia Gravis (gMG) who are anti-acetylcholine receptor (AchR) antibody positive.
Statistics
In the US, the estimated annual incidence of myasthenia gravis (number of newly diagnosed cases) has been reported as 1 in 500,000 people.[6] 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.[6][7][8] 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.[6]
Last updated: 3/9/2016
Source:
https://rarediseases.info.nih.gov/diseases/7122/myasthenia-gravis
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