Myasthenia gravis

Definition

Myasthenia gravis is a neuromuscular disorder characterized by variable weakness of voluntary muscles, which often improves with rest and worsens with activity. The condition is caused by an abnormal immune response.

Causes

In myasthenia gravis, weakness occurs when the nerve impulse to initiate or sustain movement does not adequately reach the muscle cells. This is caused when immune cells target and attack the body's own cells (an autoimmune response). This immune response produces antibodies that attach to affected areas, preventing muscle cells from receiving chemical 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 like thyrotoxicosis, rheumatoid arthritis, and systemic lupus erythematosus

Myasthenia gravis affects about 3 of every 10,000 people and can affect people at any age. It is most common in young women and older men.

Symptoms

• Vision changes:
  • Double vision
  • Difficulty maintaining steady gaze
  • Eyelid drooping
• Patients with generalized disease may also have:
  • Swallowing difficulty, frequent gagging or choking
  • Weakness or paralysis (may worsen with exertion later in the day)
  • Muscles that function best after rest
  • Drooping head
  • Difficulty climbing stairs
  • Difficulty lifting objects
  • Need to use hands to rise from sitting positions
  • Difficulty talking
  • Difficulty chewing

• Hoarseness or changing voice
• Fatigue
• Facial paralysis
• Drooling
• Breathing difficulty

Exams and Tests

Examination may be normal or may show muscle weakness that progressively worsens as the muscle is used. In many patients the eye muscles are affected first. Reflexes and sensation are normal. Weakness may affect the arms, legs, breathing or swallowing muscles and any other muscle group.

• Standard EMG results are usually normal.
• Repetitive stimulation (type of nerve conduction study) is more sensitive.
• Single-fiber EMG is even more sensitive.
• Acetylcholine receptor antibodies may be present in the blood.
• A Tensilon test is positive in some cases but must be interpreted carefully by an experienced doctor. Baseline muscle strength is evaluated. After Tensilon (edrophonium, a medication that blocks the action of the enzyme that breaks down the transmitter acetylcholine) is given, muscle function may improve.

Treatment

There is no known cure for myasthenia gravis. However, treatment may result in prolonged periods of remission.

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 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 that suppress the immune response (such as azathioprine, cyclosporine, or mycophenolate mofetil) may be used if symptoms are severe and there is inadequate response to other medications.

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 temporarily and is often used to optimize conditions before surgery.

Surgical removal of the thymus (thymectomy) may result in permanent remission or less need for medicines.

There are several medications that 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. 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. Patients that only have eye symptoms (ocular myasthenia gravis), may progress to have 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

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

When to Contact a Medical Professional

Call your health care provider if symptoms suggesting myasthenia gravis occur.

Go to the emergency room or call the local emergency number (such as 911) if breathing difficulty or swallowing problems occur.