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Myasthenia gravis

Definition

Myasthenia gravis is a neuromuscular disorder. Neuromuscular disorders involve the muscles and the nerves that control them.

Alternative Names

Neuromusclar disorder - myasthenia gravis

Causes

Myasthenia gravis causes weakness of the voluntary (skeletal) muscles. These are the muscles that create movement and are normally under your conscious control. The involuntary muscles, on the other hand, are not under conscious control (such as the muscles of your heart and many other internal organs).

In myasthenia gravis, weakness occurs because the nerve that activates a particular muscle does a poor job of stimulating that muscle. This problem occurs because immune cells (which normally attack foreign invaders) target and attack the body's own healthy cells. This is known as an autoimmune response. This autoimmune response produces antibodies that block the muscle cells from receiving messages (neurotransmitters) from the nerve cell.

The cause of autoimmune disorders such as myasthenia gravis is unknown. In some cases, myasthenia gravis may be associated with tumors of the thymus (an organ of the immune system). Patients with myasthenia gravis have a higher risk of having other autoimmune disorders, such as thyrotoxicosis, rheumatoid arthritis, and systemic lupus erythematosus (lupus).

Myasthenia gravis can affect people at any age. It is most common in young women and older men.

Symptoms

The muscle weakness of myasthenia gravis worsens with activity and improves with rest. Weakness in affected muscles may cause:

Exams and Tests

A neurological examination may be normal or may show muscle weakness that progressively worsens as the muscle is used. In many people with myasthenia gravis, the eye muscles are affected first. Reflexes and feeling (sensation) are normal. Weakness may affect the arms, legs, breathing or swallowing muscles, and any other muscle group.

Tests that may be performed:

Treatment

There is no known cure for myasthenia gravis. However, treatment may result in prolonged periods without any symptoms (remission).

Lifestyle adjustments usually enables 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 and excessive heat exposure should be avoided because they can worsen symptoms.

Some medications, such as neostigmine or pyridostigmine, improve the communication between the nerve and the muscle. Prednisone and other medications (such as azathioprine, cyclosporine, or mycophenolate mofetil) that suppress the autoimmune response responsible for the weakness may be used if symptoms are severe and other medications don't work well enough.

Plasmapheresis may reduce symptoms for 4 - 6 weeks and is often used before surgery. In this technique, the person's blood plasma (the clear part of the blood) containing the antibodies is removed from the body and replaced with donated, antibody-free plasma or with other intravenous fluids.

Intravenous immunoglobulin infusions may be as effective as plasmapheresis. In this technique, a large volume of a mixture of helpful antibodies is given directly into the bloodstream to blunt the effect of the autoimmune antibodies.

Surgical removal of 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.

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 plasmapheresis is used to help end the crisis.

Support Groups

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

Outlook (Prognosis)

There is no cure, but long-term remission is possible. There may be minimal restriction on activity in many cases. 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.

Possible Complications

  • Complications of surgery
  • Myasthenic crisis (breathing difficulty), may be life threatening
  • Restrictions on lifestyle (possible)
  • Side effects of medications (see the specific medication)

When to Contact a Medical Professional

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.

References

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. Neurology. 2007;68(24):2144-9.

Vincent A, Newsom-Davis J. Disorders of neuromuscular transmission. In: Goldman L, Ausiello D, eds. Cecil Medicine. 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. Neurology. 2007;68(11):837-41.


Review Date: 12/21/2009
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; Daniel B. Hoch, PhD, MD, Assistant Professor of Neurology, Harvard Medical School, Department of Neurology, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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