A rare disorder in which the muscles become weak and tire easily. The muscles of the eyes, face, throat, and limbs are most commonly affected.
Myasthenia gravis is an autoimmune disorder. In many cases, abnormalities in the thymus gland are present, and in some cases a thymoma is found. Women are affected more often than men.
The disease is extremely variable in its effects. In most cases, it causes drooping eyelids, double vision, a blank facial expression, and a weak, hoarse, nasal voice that is hesitant and becomes slurred during extended conversation. The arm and leg muscles may also be affected. In severe cases, the respiratory muscles may become weakened, causing breathing difficulty.
Diagnosis of the condition is often made by injecting the drug edrophonium into a vein. This temporarily restores power to the weak muscles. Blood tests and EMG are also sometimes used. CT scanning or MRI may also be performed to look for a thymoma.Treatment with drugs that facilitate transmission of nerve impulses often restores the patient’s condition to near normal.
In some cases, the condition often improves, and is sometimes cured by thymectomy (removal of the thymus gland).
Regular exchanges of the patient’s plasma for fresh plasma may be carried out in severe cases.
Corticosteroid drugs may be given.
In a minority of patients, paralysis of the throat and respiratory muscles may lead to death.
A serious disorder in which the chief symptoms are muscular weakness and a special tendency for fatigue to come on rapidly when e?orts are made. The prevalence is around 1 in 30,000. Two-thirds of the patients are women, in whom it develops in early adult life. In men it tends to develop later in life.
It is a classical example of an autoimmune disease (see AUTOIMMUNITY). The body develops ANTIBODIES which interfere with the working of the nerve endings in muscle that are acted on by ACETYLCHOLINE. It is acetylcholine that transmits the nerve impulses to muscles: if this transmission cannot be e?ected, as in myasthenia gravis, then the muscles are unable to contract. Not only the voluntary muscles, but those connected with the acts of swallowing, breathing, and the like, become progressively weaker. Rest and avoidance of undue exertion are necessary, and regular doses of neostigmine bromide, or pyridostigmine, at intervals enable the muscles to be used and in some cases have a curative e?ect. These drugs act by inhibiting the action of cholinesterase – an ENZYME produced in the body which destroys any excess of acetylcholine. In this way they increase the amount of available acetylcholine which compensates for the deleterious e?ect of antibodies on the nerve endings.
The THYMUS GLAND plays the major part in the cause of myasthenia gravis, possibly by being the source of the original acetylcholine receptors to which the antibodies are being formed. Thymectomy (removal of the thymus) is often used in the management of patients with myasthenia gravis. The incidence of remission following thymectomy increases with the number of years after the operation. Complete remission or substantial improvement can be expected in 80 per cent of patients.
The other important aspect in the management of patients with myasthenia gravis is IMMUNOSUPPRESSION. Drugs are now available that suppress antibody production and so reduce the concentration of antibodies to the acetylcholine receptor. The problem is that they not only suppress abnormal antibody production, but also suppress normal antibody production. The main groups of immunosuppressive drugs used in myasthenia gravis are the CORTICOSTEROIDS and AZATHIOPRINE. Improvement following steroids may take several weeks and an initial deterioration is often found during the ?rst week or ten days of treatment. Azathioprine is also e?ective in producing clinical improvement and reducing the antibodies to acetylcholine receptors. These effects occur more slowly than with steroids, and the mean time for an azathioprine remission is nine months.
The Myasthenia Gravis Association, which provides advice and help to sufferers, was created and is supported by myasthenics, their families and friends.
a chronic disease marked by abnormal fatigability and weakness of selected muscles, which is relieved by rest. The degree of fatigue is so extreme that these muscles are temporarily paralysed. The muscles initially affected are those around the eyes, mouth, and throat, resulting in drooping of the upper eyelids (*ptosis), double vision, *dysarthria, and *dysphagia. Myasthenia gravis is an *autoimmune disease in which acetylcholine-receptor autoantibodies bind to cholinergic receptors on muscle cells, which impairs the ability of the neurotransmitter acetylcholine to induce muscular contraction. Treatment with *anticholinesterase drugs and surgical removal of the thymus in younger patients (under the age of 45 years) lessen the severity of the symptoms. Steroid therapy, intravenous immunoglobulin treatment, and plasma exchange may be used to treat the more severely affected patients.
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