Natural Myasthenia course
The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest. Certain muscles such as those that control eye and eyelid movement, facial expression, chewing, talking, and swallowing are often, but not always, involved in the disorder. The muscles that control breathing and neck and limb movements may also be affected.
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. Thus, myasthenia gravis is an autoimmune disease because the immune system - which normally protects the body from foreign organisms - mistakenly attacks itself.
Schematic Drawing of the normal neuromuscular junction (A) and its simplification in myasthenia gravis (B). The antibodies bind to the acetylcholine (Ach) receptor preventing binding of the neurotransmitter (Ach). From Damjanov, 2000.
What is the role of the thymus gland in myasthenia gravis?
The relationship between the thymus gland and myasthenia gravis is not yet fully understood.
What are the symptoms of myasthenia gravis?
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. The degree of muscle weakness involved in myasthenia gravis varies greatly among patients, ranging from a localized form, limited to eye muscles (ocular myasthenia), to a severe or generalized form in which many muscles - sometimes including those that control breathing - are affected. Symptoms, which vary in type and severity, may include a drooping of one or both eyelids (ptosis), blurred or double vision (diplopia) 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 (dysarthria).
Who gets myasthenia gravis?
In neonatal myasthenia, the fetus may acquire immune proteins (antibodies) from a mother affected with myasthenia gravis. Generally, cases of neonatal myasthenia gravis are transient (temporary) and the child's symptoms usually disappear within 2-3 months 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.
Rarely, children may show signs of congenital myasthenia or congenital myasthenic syndrome. These are not autoimmune disorders, but are caused by defective genes that produce proteins in the acetylcholine receptor or in acetylcholinesterase.
How is myasthenia gravis diagnosed?
The first steps of diagnosing myasthenia gravis include a review of the individual's medical history, and physical and neurological examinations. The signs a physician must look 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.
A special blood test can detect the presence of immune molecules or acetylcholine receptor antibodies. Most patients with myasthenia gravis have abnormally elevated levels of these antibodies. However, antibodies may not be detected in patients with only ocular forms of the disease.
Another test is called the edrophonium test. This approach requires the intravenous administration of edrophonium chloride or Tensilon(r), a drug that blocks the degradation (breakdown) of acetylcholine and temporarily increases the levels of acetylcholine at the neuromuscular junction. In people with myasthenia gravis involving the eye muscles, edrophonium chloride will briefly relieve weakness.
A different test called single fiber electromyography (EMG), in which single muscle fibers are stimulated by electrical impulses, can also detect impaired nerve-to-muscle transmission. EMG measures the electrical potential of muscle cells. Muscle fibers in myasthenia gravis, as well as other neuromuscular disorders, do not respond as well to repeated electrical stimulation compared to muscles from normal individuals. Computed tomography (CT) may be used to identify an abnormal thymus gland or the presence of a thymoma.
A special examination called pulmonary function testing - which measures breathing strength - helps to predict whether respiration may fail and lead to a myasthenic crisis.
How is myasthenia gravis treated?
Thymectomy, the surgical removal of the thymus gland (which often is abnormal in myasthenia gravis patients), reduces symptoms in more than 70 percent of patients without thymoma and may cure some individuals, possibly by re-balancing the immune system. Other therapies used to treat myasthenia gravis include plasmapheresis, a procedure in which abnormal antibodies are removed from the blood, and high-dose intravenous immune globulin,
What are myasthenic crises?
What is the prognosis?