What is myasthenia gravis?
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 U.S., 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.
What causes myasthenia gravis?
Myasthenia gravis is not inherited, nor is contagious. A temporary form may develop in the fetus acquired through antibodies passed to the fetus from mothers with MG. Generally, neonatal forms of MG resolve in two to three 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 (acetylcholine) from stimulating muscle contraction.
What are the types of myasthenia gravis?
MG occurs rarely in children. However, there are three types of MG in children, including the following:
Congenital MG - this is a very rare, nonimmune 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 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 autoimmune 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.
What are the symptoms of myasthenia gravis?
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.
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.
How is myasthenia gravis diagnosed?
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: