Myasthenia gravis

MG, Pseudoparalytica Gravis

What is Myasthenia gravis?

Myasthenia gravis is a disorder in which normal communication between nerve and muscle is interrupted, producing weakness of muscles in the face, throat, and limbs. An affected individual characteristically has drooping eyelids, a blank facial expression, and weak, hesitant speech. Myasthenia gravis comes from Latin and Greek words meaning "grave muscle weakness.

"Myasthenia gravis is a chronic autoimmune disease in which the body's immune system mistakenly attacks and gradually destroys receptors in the muscles that are responsible for picking up nerve impulses. These receptor sites are destroyed more rapidly than can be replaced by the body. Consequently, affected muscles fail to respond, or respond only weakly, to nerve impulses. Certain muscles are most often involved and include those that control eye and mouth movements. Muscles that control breathing, and those that control movements of the arms and legs may also be affected. The muscle weakness of myasthenia gravis increases with continued activity and improves after periods of rest. Stress, infection, menstruation, and certain medications can exacerbate the conditions, making symptoms more severe. Symptoms of myasthenia gravis vary greatly from one individual to the next. The thymus gland, part of the body's immune system, is abnormally enlarged in about 75% of individuals with myasthenia gravis. In ten to fifteen percent of these cases, a tumor of the thymus gland (thymoma) is found.

Approximately only two to five new cases per 100,000 are diagnosed each year. Myasthenia gravis occurs in all races, both sexes, and at any age. It affects women more often than men (ratio of 3:2), and is most common in young adult women between the ages of 20 and 30, or in older men between the ages of 50 and 70. Myasthenia gravis is not directly inherited, nor is it contagious.

How is it diagnosed?

Myasthenia gravis signs and symptoms

Symptoms of myasthenia gravis vary greatly, not only in the way it affects different people, but also in how it affects the same person from day to day. The disease may develop suddenly or gradually.

  • Eye muscles are affected most often, resulting in drooping eyelids and double vision.
  • Weakness in the muscles of the face, throat, voice box (larynx), and neck make speaking difficult.
  • The voice becomes weak and hoarse, and may slur toward the end of the conversation.
  • The ability to chew and swallow becomes increasingly difficult as a meal progresses, increasing the risk of choking. In some cases, the jaw must be supported to keep it from hanging.
  • Arm and leg muscles may also be affected.
  • Weakness or fatigue worsens later in the day after muscles have been repetitively used.
  • In severe cases, respiratory muscles may be weakened, causing breathing difficulty.
  • Myasthenia gravis does not affect bowel and bladder function or the individual's mental capacity.

Physical exam: Muscle weakness and an abnormally enlarged thymus gland may be present. This gland, part of the immune system, is located in front of the wind pipe (trachea).

Tests: The most commonly used diagnostic test is the edrophonium test. In myasthenia gravis, when the drug (edrophonium) is injected into a vein, strength is temporarily restored to the weak muscles. Other diagnostic tests may include (records the electrical activity of muscles, showing changes in response to nerve stimulation), and a blood test for antibodies to acetylcholine (the chemical which transmits messages between nerve and muscle cells). A CT scan may be done to rule out thymoma (tumor of the thymus gland), especially in individuals over 40 years of age.

How is myasthenia gravis treated?

In mild cases, individuals may be treated with cholinergic drugs that facilitate the transmission of nerve impulses to the muscles. Also known as anticholinesterase, these drugs increase the level of acetylcholine, the substance needed to transmit nerve impulses. Often this medication is enough to restore the individual to a near normal functioning level. In severe cases, surgical removal of the thymus gland (thymectomy) reduces the production of antibodies against the acetylcholine. This often improves, and sometimes cures, the condition. Otherwise, regular plasma exchange procedures (plasmapheresis) remove abnormal antibody-containing plasma from the blood, replacing it with antibody-free plasma. High doses of anti-inflammatory drugs (corticosteroids) may be given to block the immune process.

Medications

Information Brand Generic Label Rating
Prednisone Deltasone Prednisone
Imuran Azathioprine

Activity

  • Plan activities to make the most of energy peaks. Frequent rest periods are important. Day-to-day fluctuations in symptoms are common.
  • Avoid strenuous activities and needless exposure to the sun or to cold weather.

What might complicate it?

Excessive physical or emotional stress may trigger a "myasthenic crisis." This crisis is a serious condition in which the individual rapidly develops widespread weakness, including weakness of the respiratory muscles. The individual may temporarily require the use of mechanical ventilation.

Predicted outcome

Although there is no known cure for myasthenia gravis, medical treatment usually reduces the symptoms. Some individuals may achieve complete remission (absence of symptoms). Most individuals can expect to lead normal or near-normal lives. In a minority of individuals, progression of the disease cannot be halted. Paralysis of the throat and respiratory muscles may lead to death.

Alternatives

Eaton-Lambert syndrome, botulism, barium poisoning, diptheria, and Guillain-Barr' have similar presentations.

Appropriate specialists

Neurologist and rheumatologist.

Notify your physician if

  • You or a family member has symptoms of myasthenia gravis.
  • You develop swallowing or breathing difficulty. You should have emergency medications (anticholinesterase drugs) available at all times to use if symptoms develop.

Last updated 6 October 2011


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