Myasthenia gravis

Causes and Risks:
Myasthenia gravis involves fluctuating levels of weakness of commonly used muscles. Weakness occurs when the nerve impulse does not adequately reach the muscle cells; this is caused by blockage of the action of transmitters (the chemicals that transmit signals from nerve cell to muscle cell). This is thought to be the result of an immune response of the body against itself (an autoimmune response). High levels of antibodies block the action of specific chemicals that are used to transmit messages from the nerve cell to the muscle cell (neurotransmitters).

The cause of autoimmune disorders such as myasthenia gravis is unknown. In some cases, it may be associated with tumors of the thymus (a tissue of the immune system). It also may be associated with thyrotoxicosis , rheumatoid arthritis , systemic lupus erythematosus , and other immune system disorders. In many cases, no other disorder is identified.

Myasthenia gravis affects about 3 out of 10,000 people. Except when the disorder is associated with thymus tumor (which is most common in elderly men), myasthenia gravis is most common in adult women. Symptoms may worsen with pregnancy or menstrual periods.

Pediatric myasthenia gravis can be distributed into 3 groups:
  • neonatal myasthenia (develops in a newborn)
  • congenital myasthenia (already present at birth)
  • onset any time after birth, although before 1 year of age is rare



Prevention:
There is no known way to prevent this disorder.

Symptoms:

Additional symptoms that may be associated with this disease:



Signs and Tests:
Examination may be normal or may show muscle weakness that progressively worsens as the muscle is used. Reflexes and sensation are normal. Weakness may affect the arms; legs; the muscles for breathing, swallowing, talking, or any muscle group. Facial involvement is usually early. Eyelids may droop.

  • EMG results vary.
  • Repetitive stimulation nerve conduction studies are more productive (studies of nerve impulse conduction, performed as the nerve supplying the muscles is repeatedly stimulated).
  • Acetylcholine receptor antibodies may be present in the blood.
  • A Tensilon test is positive in most cases. A baseline muscle strength evaluation is performed. After Tensilon (edrophonium; a medication that blocks the action of the enzyme that breaks down the transmitter acetylcholine) is given, muscle function improves noticeably.

This disease may also alter the results of the following tests:



Treatment:
There is no known cure for myasthenia gravis. However, treatment may result in prolonged periods of remission, without symptoms.

Medications, including anticholinesterase medications such as Neostigmine or Pyridostigmine, should be given 30 minutes before meals to maximize the ability to eat and swallow. Prednisone or other medications that suppress the immune response may be used if symptoms are severe and there is inadequate response to other medications. Some medications (such as the aminoglycosides) may make symptoms worse and should be avoided.

Lifestyle adjustments may enable continuation of many activities. Activity should be planned to allow scheduled rest periods. An eye patch may be recommended if double vision is bothersome. Stress should be avoided, because it worsens symptoms.

Plasmapheresis, a technique in which blood plasma containing antibodies against the body is removed from the body and replaced with fluids (donated antibody-free plasma or other intravenous fluids), may reduce symptoms in some cases.

Surgical removal of the thymus (thymectomy) results in permanent remission for many people.

Crisis situations, where muscle weakness involves the breathing muscles, may occur. These attacks seldom last longer than a few weeks. Hospitalization and assistance with breathing may be required during these attacks.

The stress of illness can often be helped by joining support groups where members share common experiences and problems. See myasthenia gravis - support group .

Prognosis:
There is no cure, but long-term remission is possible. There may be minimal restriction on activity in many cases. Pregnancy is possible but should be closely supervised; the baby may require medications for a few weeks after birth but usually does not develop the disorder.

Complications:

  • restrictions on lifestyle (possible)
  • side effects of medications (See the specific medication.)
  • complications of surgery
  • myasthenic crisis ( breathing difficulty ), may be life threatening



Call Your Healthcare Provider:
Call your health care provider if the symptoms indicate myasthenia gravis may be present.

Go to the emergency room or call the local emergency number (such as 911) if myasthenia gravis has been diagnosed and breathing difficulty occurs (emergency situation).