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Myasthenia gravis (MG) is a chronic disease that weakens the voluntary muscles — the ones you control — in a telltale way: the weakness gets worse with activity and better with rest. It is an autoimmune disease: the immune system attacks the body's own healthy tissue by mistake.
What goes wrong
Normally, a signal travels down a nerve to a muscle, and the nerve endings release a chemical called acetylcholine, which binds to the muscle at the nerve-muscle junction and makes it contract. In myasthenia gravis, the immune system makes antibodies that block acetylcholine from binding, so the signal does not get through and the muscle is weaker.
The thymus gland may play a part. Part of the immune system, it is active and growing in childhood, making white blood cells; after puberty it shrinks and is replaced by fat. But in many adults with MG the thymus stays large, and some develop thymomas — thymus tumors that are usually benign but can become cancerous.
Who gets it
- It can occur at any age, but is most common in young adult women (under 40) and older men (over 60).
- It is usually not inherited.
- It normally doesn't affect infants — but a pregnant woman with MG can pass the antibodies to her fetus, and the baby may be born with neonatal myasthenia, which is usually temporary; symptoms typically go away within two to three months.
Symptoms
Which symptoms appear depends on which muscles are affected, and how weak they are varies from person to person and from day to day:
- weak eye muscles, drooping eyelids, and blurred or double vision
- changes in facial expression
- trouble swallowing, speech problems, shortness of breath
- weakness in the arms, hands, fingers, legs and neck
A myasthenic crisis — severe weakness of the muscles that control breathing — is a life-threatening emergency.
Diagnosis
Because many conditions cause muscle weakness, MG can be hard to diagnose. A provider takes a history, does a physical and neurological exam, and will likely order blood tests, imaging, and electromyography (EMG) with nerve conduction studies.
Treatment
There is no cure, but treatment can improve weakness and symptoms.
| Treatment | What it does |
|---|---|
| Anticholinesterase medicines | Improve nerve-to-muscle messages and strengthen muscles |
| Immunosuppressive medicines | Damp the immune response and the production of abnormal antibodies |
| Monoclonal antibodies | Also damp the immune response |
| Plasmapheresis (plasma exchange) and intravenous immunoglobulin | Remove abnormal antibodies from the blood; usually for severe cases, and help for weeks or months |
| Thymectomy | Surgery to remove the thymus; can reduce symptoms, possibly by rebalancing the immune system |
Regular gentle exercise, enough rest and healthy food may help some people. Some go into remission, free of symptoms — usually temporarily, sometimes for good.
Sources
Based on "Myasthenia Gravis," MedlinePlus, National Library of Medicine, drawing on the National Institute of Neurological Disorders and Stroke; a work of the United States government in the public domain.
Лицензия: CC0 1.0 (общественное достояние) · По материалам medlineplus.gov
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