Myasthenia gravis (MG) is an autoimmune disease. It affects the connection between the nerves and skeletal muscles. This can cause progressive muscle weakness.
The root cause of MG is unknown. It occurs when the body’s immune system attacks receptors in muscle. Normally, these receptors respond to the chemical acetylcholine (ACh). This chemical allows nerve signals to prompt the muscles to move. When the immune system prevents these receptors from working well, the muscles cannot respond to nerve signals.
The thymus is thought to play a role in some cases of MG. The thymus is an organ behind the breastbone. Immune proteins called antibodies are produced there. It is these antibodies that may target the ACh receptors. It is still not clear why the thymus begins to produce these.
The Thymus Gland
Infants of mothers with MG are more likely to develop a temporary form. It is called neonatal MG. The mother’s abnormal antibodies enter the baby’s bloodstream. When the baby is born, there may be muscle weakness. The abnormal antibodies are often cleared from the baby in about 2 months. This will end the baby’s symptoms.
MG is most common in women less than 40 years old and in men over 60 years old.
Symptoms may grow more severe over time. MG may cause the following:
- Muscle weakness that increases with muscle use/exercise, and improves after resting those muscles
- Drooping eyelids
- Double and/or blurred vision
- Difficulty swallowing
- Difficulty speaking
- Difficulty walking
- Weakness of the hand muscles
- Difficulty breathing
Your doctor will ask about your symptoms and medical history. A physical exam will be done. You will likely need to see a neurologist. This type of doctor is an expert in diseases of the nervous system. Tests may include:
- Blood tests
- Electromyography (EMG) tests—to reveal abnormalities in muscle functioning
- Repetitive nerve stimulation (a component of EMG)—may show progressively increasing muscle weakness over the course of the test
- Tensilon test—a dose of a medication called edrophonium chloride is given, which will briefly improve muscle weakness
- Pulmonary function testing to evaluate breathing an lung function
Imaging tests to see internal bodily structures may be done with:
- CT scan
- MRI scan
Treatment is focused on managing MG symptoms. Talk with your doctor about the best treatment plan for you. Options may include one or more of the following:
Your doctor may prescribe the following:
- Acetylcholinesterase inhibitors
- Immunosuppressive drugs
- IV immunoglobulin therapy
Plasmapheresis is a procedure that cleans the blood of the abnormal antibodies. This process may need to be repeated at certain intervals.
Thymectomy is a surgical procedure to remove the thymus gland. Surgery may improve symptoms or bring remission in some people.
This may only be needed if breathing is severely impaired. This can happen during an episode of myasthenic crisis.
Physical and Occupational Therapy
Therapy does not generally alter the course of the disease. It may be needed to help the person cope with changes in muscle strength. It may also help with learning alternative ways to approach daily activities.
There are no current guidelines to prevent MG.
Myasthenia Gravis Foundation of America
National Institute of Neurological Disorders and Stroke
Myasthenia Gravis Association of BC
Public Health Agency of Canada
Gronseth GS, Barohn RJ. Practice parameter: Thymectomy for autoimmune myasthenia gravis (an evidence-based review): Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2000;55(1):7-15.
Myasthenia gravis. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated June 27, 2014. Accessed August 21, 2014.
Myasthenia gravis fact sheet. National Institute of Neurological Disorders and Stroke website. Available at: http://www.ninds.nih.gov/disorders/myasthenia_gravis/detail_myasthenia_gravis.htm. Updated April 16, 2014. Accessed August 21, 2014.
What is myasthenia gravis (MG)? Myasthenia Gravis Foundation of America website. Available at: http://www.myasthenia.org/WhatisMG.aspx. Accessed August 21, 2014.
Last reviewed August 2015 by Rimas Lukas, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.