Myasthenia gravis is a neuromuscular disorder. Neuromuscular disorders involve the muscles and the nerves that control them.
Causes, incidence, and risk factors
Myasthenia gravis is a type of autoimmune disorders . An autoimmune disorder occurs when the immune system mistakenly attacks healthy tissue. In people with myasthemia gravis, the body produces antibodies that block the muscle cells from receiving messages (neurotransmitters) from the nerve cell.
The exact cause of myasthenia gravis is unknown. In some cases, it may be associated with tumors of the thymus (an organ of the immune system).
Myasthenia gravis can affect people at any age. It is most common in young women and older men.
Myasthenia gravis causes weakness of the voluntary (skeletal) muscles. Voluntary muscles are those that are under your control. In other words, you think about moving your arm, and it moves. The muscle weakness of myasthenia gravis worsens with activity and improves with rest.
The muscle weakness can lead to a variety of symptoms, including:
Signs and tests
The health care provider performs a physical exam, including a detailed nervous system (neurological) examination. This may show:
- Muscle weakness - eye muscles are usually affected first
- Reflexes and feeling (sensation) are normal.
Tests that may be done may include:
There is no known cure for myasthenia gravis. However, treatment may allow you to have prolonged periods without any symptoms (remission).
Lifestyle changes often help you continue your daily activities. The following may be recommended:
- Scheduling rest periods
- An eye patch if double vision is bothersome
- Avoiding stress and heat exposure, which can make symptoms worse
Medications that may be prescribed include:
- Neostigmine or pyridostigmine to improve the communication between the nerves and the muscles
- Prednisone and other medications (such as azathioprine, cyclosporine, or mycophenolate mofetil) if to suppress the immune system response, if you have severe symptoms and other medicines have not worked well
Several medications may make symptoms worse and should be avoided. Therefore, it is always important to check with your doctor about the safety of a medication before taking it.
Crisis situations, where muscle weakness involves the breathing muscles, may occur without warning with under- or overuse of medications. These attacks seldom last longer than a few weeks. Hospitalization and assistance with breathing may be required during these attacks. Often procedure called plasmapheresis is used to help end the crisis. In this technique, the clear part of the blood (plasma) containing the antibodies is removed from the body and replaced with donated, antibody-free plasma or with other fluids.
Plasmapheresis may also help reduce symptoms for 4 - 6 weeks and is often used before surgery. Intravenous immunoglobulin infusions may work as well as plasmapheresis. In this technique, a large amount of helpful antibodies are given directly into the bloodstream.
Surgery to remove the thymus (thymectomy) may result in permanent remission or less need for medicines, especially when there is a tumor present.
Patients with eye problems may try lens prisms to improve vision. Surgery may also be performed on the eye muscles.
The stress of illness can often be helped by joining support groups where members share common experiences and problems. See: Myasthenia gravis - support group
There is no cure, but long-term remission is possible. You may have to restrict some daily activities. People who have only eye symptoms (ocular myasthenia gravis), may develop generalized myasthenia over time.
Pregnancy is possible for a woman with myasthenia gravis but should be closely supervised. The baby may be temporarily weak and require medications for a few weeks after birth but usually does not develop the disorder.
The condition may cause life-threatening breathing problems. This is called a myasthetnic crisis.
Patients with myasthenia gravis have a higher risk of having other autoimmune disorders, such as thyrotoxicosis , rheumatoid arthritis , and systemic lupus erythematosus (lupus).
Calling your health care provider
Call your health care provider if you develop symptoms of myasthenia gravis.
Go to the emergency room or call the local emergency number (such as 911) if you have breathing difficulty or swallowing problems.
Benatar M, Kaminski HJ. Evidence report: the medical treatment of ocular myasthenia (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology. . 2007;68(24):2144-9.
Vincent A, Newsom-Davis J. Disorders of neuromuscular transmission. In: Goldman L, Ausiello D, eds. . 23rd ed. Philadelphia, Pa: Saunders Elsevier. 2007: chap 448.
Zinman L, Ng E, Bril V. IV immunoglobulin in patients with myasthenia gravis: a randomized controlled trial. . 2007;68(11):837-41.