Myasthenia gravis is a chronic autoimmune neuromuscular disease characterized by an abnormal fatigability of muscles due to malfunctioning of the myoneural junction.

The name myasthenia gravis is derived from Latin and Greek words that literally means “grave muscle weakness.” It is caused by a defect in the transmission of nerve impulses to muscles. It occurs when normal communication between the nerve and muscle is interrupted at the neuromuscular junction. Auto antibodies produced against acetyl choline receptors block, alter, or destroy the acetylcholine receptors of striated muscles at the neuromuscular junction.

In the absence of acetyl choline receptors nerve impulses fails to reach the muscle ensuing failure of muscle contraction followed by weakness and rapid fatigue in the affected muscles. It occurs in all ethnic groups and both genders.

Most commonly it affects young adult women (under 40) and older men (over 60), but it can occur at any age.

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Certain muscles such as those that control eye and eyelid movement, facial expression, chewing, talking, and swallowing are often, but not always, involved in the disorder. The muscles that control breathing, movements of neck and limb may also be affected.

In neonatal myasthenia the auto antibody is passively acquired from the mother.

A special blood test can detect the presence of immune molecules or acetylcholine receptor antibodies.

Most patients with myasthenia gravis have abnormally elevated levels of these antibodies.

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Another test is called the edrophonium test. This approach requires the intravenous administration of edrophonium chloride or Tensilon(r), a drug that blocks the degradation (breakdown) of acetylcholine and temporarily increases the levels of acetylcholine at the neuromuscular junction.

In people with myasthenia gravis involving the eye muscles, edrophonium chloride will briefly relieve weakness.

A different test called single fiber electromyography (EMG), in which single muscle fibers are stimulated by electrical impulses, can also detect impaired nerve- to-muscle transmission. EMG measures the electrical potential of muscle cells.

Muscle fibers in myasthenia gravis, as well as other neuromuscular disorders, do not respond as well to repeated electrical stimulation compared to muscles from normal individuals.

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There are several therapies available to help, reduce and improve muscle weakness. Medications used to treat the disorder include anticholinesterase agents such as neostigmine and pyridostigmine, which help improve neuromuscular transmission and increase muscle strength.

Immunosuppressive drugs such as prednisone, cyclosporine, and azathioprine may also be used. These medications improve muscle strength by suppressing the production of abnormal antibodies. Thymectomy, the surgical removal of the thymus gland (which often is abnormal in myasthenia gravis patients), reduces symptoms in more than 70 percent of patients without thymoma and may cure some individuals, possibly by re­balancing the immune system.

Other therapies used to treat myasthenia gravis include plasmapheresis, a procedure in which abnormal antibodies are removed from the blood, and high-dose intravenous immune globulin, which temporarily modifies the immune system and provides the body with normal antibodies from donated blood. These therapies may be used to help individuals during especially difficult periods of weakness.