Definition Myasthenia gravis is a disease in which the body's immune system attacks the muscles and causes weakness. This disorder occurs more frequently in women than men and usually begins between the ages of 20 and 40.
What is going on in the body? Myasthenia gravis is known as an autoimmune disorder. An autoimmune disorder is one in which a person's immune system attacks the body for unknown reasons. In myasthenia gravis, antibodies are produced that attack the muscles in the body.
What are the signs and symptoms of the disease? Symptoms tend to be worse toward the end of the day or after prolonged muscle use. These include:
What are the causes and risks of the disease? The reason the body produces antibodies against the muscles is not well understood. The antibodies destroy the part of the muscle that receives signals from the nerves. When the muscle is less able to receive nerve signals, the muscle doesn't work properly and the person becomes weak. One of the risks of myasthenia is difficulty breathing because of chest muscle weakness. Severe weakness may require the person to be put on a ventilator, or artificial breathing machine, temporarily. In addition, someone with myasthenia gravis has a high risk of developing a tumour in the thymus gland.
What can be done to prevent the disease? There are no known ways to prevent myasthenia gravis.
How is the disease diagnosed? A Tensilon test can be done to diagnose myasthenia gravis. A medication called Tensilon is given to the person intravenously, or into a vein. If the person has myasthenia gravis, the Tensilon will temporarily strengthen the person's muscles.
Electromyography, or EMG, can be done to measure the way the muscles respond to electrical stimulation. When myasthenia is present, an abnormal response to electrical shocks occurs in the muscles. A blood test, known as antibody titre, can often detect the antibodies that attack the muscles.
What are the long-term effects of the disease? Myasthenia gravis often has an unpredictable course and may get better or worse over time. The primary long-term effects are the risk of tumours in the thymus gland, breathing problems, and the side effects of treatment.
What are the risks to others? There are no risks to others, as myasthenia gravis is not contagious.
What are the treatments for the disease? Treatment often involves medication and surgery. Surgery to remove the thymus gland eliminates the risk of tumours and often improves symptoms. This surgery is recommended in a person who is otherwise healthy. Medications are given to improve the strength of the muscles. One muscle-strengthening medication used in myasthenia is pyridostigmine. Since myasthenia gravis is an autoimmune disorder, powerful medications to suppress the immune system are required if initial treatment fails.
What are the side effects of the treatments? Surgery has a risk of bleeding, infection, and even death. Medications can cause allergic reactions, stomach upset, diarrhoea and other side effects. Medications used to suppress the immune system can increase the person's risk of infections.
What happens after treatment for the disease? If the person improves, he or she can resume normal daily activities. Some people require intense treatment for long periods of time.
How is the disease monitored? Any new or worsening symptoms should be reported to the doctor. Medications may need to be monitored with blood tests.
Author: Adam Brochert, MD Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
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