The distinctive feature of myasthenia gravis is muscle weakness that increases during periods of activity and improves after rest. Muscles that control eye and eyelid movements, facial expression, chewing, talking, and swallowing are often, but not always, involved. The muscles that control breathing and neck and limb movements may also be affected. These muscles are called voluntary or striated muscles. Involuntary heart muscle and smooth muscles of the gut, blood vessels, and uterus are not involved in MG.
The onset of MG may be sudden and often not immediately recognized. In most cases, the first noticeable symptom is weakness of the eye muscles. In others, difficulty in swallowing and slurred speech may be the first signs.
Muscle weakness may develop over a few days or weeks, or remain at the same level for long periods of time. The degree of muscle weakness involved in myasthenia gravis varies greatly among patients; it may be limited to eye muscles but may take a more generalised form in which many muscles - sometimes including those that control breathing - are affected. Symptoms may include a drooping of one or both eyelids, blurred or double vision due to weakness of the muscles that control eye movements, unstable or waddling gait, weakness in arms, hands, fingers, legs, and neck, a change in facial expression, difficulty in swallowing and shortness of breath, and impaired speech.
A myasthenic crisis, usually triggered by infection, fever, emotional stress or adverse reaction to medication, may occur when weakness affects the muscles that control breathing. The patient requires a respirator for assisted ventilation.
MG is an autoimmune disease – a disease where the immune system, which normally protects the body from foreign organisms, mistakenly attacks itself. In MG antibodies produced by the body’s own system interrupt the transmission of nerve impulses to muscles, preventing normal muscle contractions from occurring.
Myasthenia gravis occurs in all ethnic groups and both genders but most commonly affects young adult women (under 40) and older men (over 60). It can however occur at any age.
Unfortunately, a delay in diagnosis of one or two years is not unusual in cases of myasthenia gravis. Because weakness is a common symptom of many other disorders, the diagnosis is often missed in people who experience only mild weakness or in those whose weakness is restricted to only a few muscles. The signs the physician looks for are impairment of eye movements or muscle weakness without any changes in the individual's ability to feel things. If the doctor suspects myasthenia gravis, several tests are available to confirm the diagnosis.
In neonatal myasthenia, the foetus may acquire immune proteins (antibodies) from a mother affected with myasthenia gravis. Generally, cases of neonatal myasthenia gravis are temporary and the child's symptoms usually disappear within few weeks after birth. Other children develop myasthenia gravis indistinguishable from adults. Myasthenia gravis in juveniles is common.
Myasthenia gravis is not directly inherited nor is it contagious. Occasionally, the disease may occur in more than one member of the same family.
To-day myasthenia can be controlled by the use of two types of medication to reduce muscle weakness. One type improves the transmission of nerve impulses to muscles, the other suppresses the production of abnormal antibodies. The use of these medications must be carefully supervised as they may have major side effects.
The surgical removal of the thymus gland (which lies in the upper chest area beneath the breastbone and plays an important part in the early development of the immune system) improves symptoms in more than 50% of patients and may cure some by rebalancing the immune system.
Another therapy used to treat MG is a procedure which temporarily removes abnormal antibodies from the blood and provides the body with normal antibodies from donated blood.
A neurologist will determine the appropriate treatment for each patient depending on the severity of the weakness, which muscles are affected, the individual’s age and other medical problems.
The name myasthenia gravis, which is Latin and Greek in origin, literally means ‘grave muscle weakness.’ With current treatment, however, most cases of myasthenia gravis are not as ‘grave’ as the name implies. In fact, for the majority of individuals with myasthenia gravis, life expectancy is not decreased by the disorder.
With treatment, the outlook for most patients is bright. They will have significant improvement of their muscle weakness and can expect to lead normal or nearly normal lives. Some cases of myasthenia gravis may go into remission temporarily and muscle weakness may disappear completely so that medications can be discontinued. Stable, long-lasting complete remissions are the goal of surgery.
Further Information and Support
The Australian Myasthenic Association in NSW
Myasthenia Gravis Association of Queensland
National Institute of Neurological Diseases and Stroke
Myasthenia Gravis Foundation of America
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Reviewed by Dr Dominic Rowe, Neurologist, Royal North Shore Hospital, Australia