|
Myasthenia Gravis - The Resource
|
|||||
|
|
What is myasthenia gravis? Myasthenia Gravis is a disease which appears to the sufferer to weaken the muscles. It is a disorder of the junction between the nerve and the muscle, caused by the body's immune system attacking a vital part of this junction - this impairs the ability of the nerve to cause muscle contraction, and hence produces the apparent weakness. IntroductionThe defining feature of myasthenia gravis is painless muscle weakness that fatigues - in other words the muscles weaken more rapidly on use than is normal. In addition, the symptoms typically worsen towards the end of the day and after exercise. Myasthenia gravis affects about one person in every 10,000. The disorder can start at any age from childhood onwards and the chance of developing it increases with age. In the younger age group, women are affected about twice as often as men are. However, in later life it is commoner in men than women. The prognosis of myasthenia gravis is good. Using the array of therapies that are now available, more than 90 percent of patients return to near-normal function. SymptomsBetween patients, the disease varies widely in severity and pattern of progression. In the early stages, the weakness can be intermittent. Often the first sign is drooping of the eyelids or double vision. About 15 percent of patients only ever have eye muscle weakness – this is called ocular myasthenia. The others also have more widespread weakness - generalized myasthenia. These patients can develop weakness of the face, swallowing, and chewing muscles, slurring of speech, and weakness of the limbs and neck. In severe cases, weakness of the breathing muscles can occur. Problems with swallowing or coughing can cause choking. Chronic fatigue without weakness is not a feature of myasthenia. CausesMyasthenia gravis is an autoimmune disease caused by abnormal antibodies carried in the blood stream. Nerves release a chemical called acetylcholine that activates receptors on muscles to trigger contraction. The myasthenia antibodies interfere with this process by binding to specific sites on the surface of the muscles. The commonest antibodies are directed against the muscle acetylcholine receptor. In 75 per cent of patients, the abnormal antibody production is associated with abnormalities of a gland in the chest called the thymus, which is part of the immune system. About 10 per cent of patients have a tumor of the thymus (a thymoma) that is usually benign. There are very rare genetic abnormalities that cause problems similar to myasthenia gravis. These diseases are called congenital or inherited myasthenias and usually present in infants. DiagnosisIn most patients, blood tests can detect the antibodies that cause myasthenia gravis. Electromyography (EMG) is a very sensitive method to assess the changes in muscle electrical activity caused by myasthenia. Sometimes an injection of the drug edrophonium hydrochloride is given (the Tensilon test), which causes a swift but brief improvement in most patients’ muscle weakness. Many patients have a chest CT scan to assess the size and shape of the thymus gland. TreatmentAcetylcholine is broken down in the body by enzymes called cholinesterases. This action can be blocked by anticholinesterase drugs such as pyridostigmine. These drugs can control myasthenia in some patients but many others need additional treatment. Surgical removal of the thymus gland (thymectomy) is performed in patients with a thymoma and can also help some other patients, especially those who develop myasthenia before the age of about 45. Drugs such as prednisolone (a steroid) and azathioprine that suppress the immune system are often used in patients with disabling weakness, especially those who do not have, or fail to respond to, thymectomy. When rapid improvement is needed, for example severe weakness causing breathing or swallowing problems, patients can be admitted to hospital for plasma exchange, which removes antibodies from the blood. Another option is an infusion of intravenous immunoglobulin. The benefits of these emergency treatments last only for about six weeks. Please also see "Research vs. Reality" on this website for more information and terms related to the disease.
Additional links
|
||||
