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Myasthenia gravis (MG) is a chronic, complex, autoimmune disorder in which antibodies destroy neuromuscular connections. This causes problems with communication between nerves and muscle, resulting in weakness of the skeletal muscles. MG affects the voluntary muscles of the body, especially the eyes, mouth, throat, and limbs.
In the US, MG affects about 20 people in 100,000. Women affected by MG generally see onset of the condition by age 20 to 30; the onset of MG in men most commonly occurs after the age of 50. However, MG can occur at any age. Males are more often affected than females.
Myasthenia gravis is not inherited, nor is contagious. A temporary form may develop in the fetus acquired through antibodies passes to the fetus from mothers with MG. Generally, neonatal forms of MG resolve in 2 to 3 months. The disorder generally develops spontaneously later in life as a result of antibodies made in the persons body which attack normal receptors on muscle, to which nerves send impulses. This blocks the chemical released by the nerve endings (acetycholine) from stimulating muscle contraction.
MG occurs rarely in children. However, there are three types of MG in children, including the following:
- Congenital MG - this is a very rare, non-immune form of MG that is inherited as an autosomal recessive disease. This means that both males and females are equally affected and that two copies of the gene, one inherited from each parent, are necessary to have the condition. Symptoms of congenital MG usually begin in the baby's first year and are life-long.
- Transient neonatal MG - between 12 percent and 20 percent of babies born to mothers with MG may have a temporary form of MG. This occurs when antibodies common in MG cross the placenta to the developing fetus. Neonatal MG usually lasts only a few weeks, and babies are not at greater risk for developing MG later in life.
- Juvenile MG - this auto-immune disorder develops typically in female adolescents - especially Caucasian females. It is a life-long condition that may go in and out of remission. About 10 percent of MG cases are juvenile-onset.
In adults, MG may occur at any age, although symptoms begin to appear more often between the ages of 20 to 30 in women and between the ages of 50 to 60 in men.
The following are the most common symptoms of myasthenia gravis. However, each individual may experience symptoms differently. Symptoms may include:
- Visual problems, including drooping eyelids (ptosis) and double vision (diplopia) - about two-thirds of persons with MG have symptoms such as these at first.
- Severe muscle weakness and fatigue that may vary rapidly in intensity over days or even hours and worsen as muscles are used (early fatigue)
- Facial muscle involvement causing a mask-like appearance; a smile may appear more like a snarl
- Difficulty in swallowing and/or pronouncing words
- Weakness of the neck and/or limbs
The symptoms of myasthenia gravis may resemble other conditions. Always consult your physician for a diagnosis.
Exacerbations (worsening of symptoms) and remissions (easing of symptoms) may occur periodically during the course of MG. Remissions, however, are only rarely permanent or complete.
The diagnosis of myasthenia gravis is made after the sudden or gradual onset of specific symptoms and after diagnostic testing. During the physical examination, the physician obtains a complete medical history, and may also ask if there is a family history of any medical problems.
A primary characteristic of MG results in the response of an affected person to certain medications. When given an anticholinesterase medication, such as neostigmine (Prostigmin) or edrophonium (Tensilon), muscle weakness often dramatically improves for a brief time. This provides strong support for the diagnosis of MG.
Other diagnostic tests that may be performed to help confirm the diagnosis of myasthenia gravis include:
- Blood tests - these tests look for antibodies that may be present in people with mayasthenia gravis: anti-acetylcholine receptor antibodies are present in the blood of over 85 percent of affected persons; anti-MuSK antibodies have been found in about 30 to 40 percent of people with MG who do not have acetlcholine receptor antibodies.
- Genetic tests - diagnostic tests that evaluate for conditions that have a tendency to run in families.
- Electromyogram (EMG) - a test that measures the electrical activity of a muscle or a group of muscles. An EMG can detect abnormal electrical muscle activity due to diseases and neuromuscular conditions.
Specific treatment for myasthenia gravis will be determined by your physician based on:
- Your age, overall health, and medical history
- Extent of the condition
- Your tolerance for specific medications, procedures, or therapies
- Expectations for the course of the condition
- Your opinion or preference
There is no cure for MG, but the symptoms can generally be controlled. Myasthenia gravis is a life-long medical condition and the key to medically managing MG is early detection.
The goal of treatment is to increase general muscle function and prevent secondary respiratory and nutritional problems since the swallowing and breathing muscles are affected by this condition. Most persons with MG can improve their muscle strength and lead normal or near normal lives. In more severe cases, respiratory or nutritional support may be required due to breathing or swallowing difficulty.
Treatment may include:
- Medications - anticholinesterase medications, such as Prostigmin or Tensilon; steroids; and/or immunosuppressive (suppress the immune system’s response) medications may be used.
- Thymectomy - surgical removal of the thymus gland. The role of the thymus gland in MG is not fully understood, and the thymectomy may or may not improve symptoms. However, thymectomy reduces symptoms in more than 70 percent of patients who do not have cancer of the thymus, possibly by altering the immune system response, according to the National Institute of Neurologic Disorders.
- Plasmapheresis - a procedure that removes abnormal antibodies from the blood and replaces the blood with normal antibodies through donated blood.
- Immunoglobulin - a blood product that helps to decrease the immune system’s attack on the nervous system, given intravenously (IV).
The extent of the problems is dependent on the severity of the condition and the presence of other problems that could affect the individual. In severe cases, a breathing machine may be required to help the person breathe easier.
The healthcare team educates the family after hospitalization on how to best care for the person at home and outlines specific clinical problems that require immediate medical attention by their physician. A person with MG requires frequent medical evaluations throughout his/her life.
It is important to allow as much independent function and self care as possible and to promote appropriate activities to ensure a sense of normalcy.
Myasthenia crisis is a condition of extreme muscle weakness, particularly of the diaphragm and chest muscles that support breathing. Myasthenia crisis may be caused by a lack of MG medication or by other factors, such as a respiratory infection, emotional stress, surgery, or some other type of stressor. In severe crisis, a person may have to be placed on a ventilator to assist breathing until muscle strength returns with treatment.
Precautions, which may help to prevent or minimize the occurrence of myasthenia crisis, include, but are not limited to, the following:
- Taking anticholinesterase medications 30 to 45 minutes prior to meals to reduce the risk of aspiration (food entering the lung passages)
- Taking anticholinesterase medications precisely as ordered by the physician to help maintain the strength of the breathing muscles
- Avoiding crowds and contact with people with respiratory infections, such as a cold or the flu
- Taking in proper nutrition to maintain optimal weight and muscle strength
- Alternate performance of physical activities with periods of rest
- Using stress-reduction techniques and avoiding emotional extremes
- Notify any healthcare provider of your condition when any medications are being prescribed, as certain medications may interfere either with the disease or the action of the medications you take for MG
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