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By Mayo Clinic staff
Myasthenia gravis (mi-uhs-THEE-ne-uh GRA-vis) is characterized by weakness and rapid fatigue of any of the muscles under your voluntary control. The cause of myasthenia gravis is a breakdown in the normal communication between nerves and muscles.
There is no cure for myasthenia gravis, but treatment can help relieve signs and symptoms — such as weakness of arm or leg muscles, double vision, drooping eyelids, and difficulties with speech, chewing, swallowing and breathing.
While myasthenia gravis can affect people of any age, it's more common in women younger than 40 and in men older than 60.
# For more info on Myasthenia gravis from the Mayo Clinic, visit: http://www.mayoclinic.com/health/myasthenia-gravis/DS00375
below as posted by The Muscular Dystrophy Association
In recognition of June being National Myasthenia Gravis Awareness Month, Quest News Online is examining the disease from several perspectives. This article offers an overview of signs, symptoms, diagnosis and treatments for myasthenia gravis (MG), as well as some drugs for people with MG to avoid.
As one of the 43 diseases in MDA's program, MG is also the focus of more than a dozen current MDA-funded research projects. These projects, described below, range from identification of genetic causes and molecular underpinnings to development of potential new treatments.
MG is part of a large class of diseases known as "autoimmune," or "self-immune," disorders, in which the body's immune system deploys antibodies (proteins that identify and attack bacteria and other foreign substances) to attack its own tissues.
In MG, the attack occurs at the neuromuscular junction (NMJ) — the connection between muscle and nerve.
In most cases of MG, the immune system targets the acetylcholine receptor, the part of a muscle cell that receives signals from a nerve cell. The receptors are destroyed faster than the body can replace them. Another form of the disease is characterized by an attack on muscle-specific kinase, a protein that helps organize acetylcholine receptors on the muscle cell.
It remains unclear what triggers the disease, but the list of possibilities includes autoimmune responses to viruses or bacteria, and tumors or hyperactivity in the thymus gland, located in the upper chest.
Signs and symptoms
Some 10 to 15 out of every 100,000 Americans have MG, which most commonly affects women between the ages of 30 and 40, and men in their 50s or 60s. In some cases, it affects children. Symptoms vary in type and severity, but generally involve weakness and fatigue of the body's voluntary muscles.
Early symptoms often include weakness in the muscles that control movement of the eyes and eyelids, sometimes leading to partial paralysis of eye movements, double vision and droopy eyelids.
Weakness in the neck and jaw, called "bulbar" weakness, also can occur early in MG. Such weakness can make it difficult to talk, chew, swallow and hold up the head. It also may affect speech, cause choking, and make eating unpleasant or difficult.
Typically, as the disease progresses, weakness spreads from the face and neck to the upper limbs, the hands and then the lower limbs. People with MG may find it difficult to raise their arms over their head or stand up from a sitting position. They may lose the ability to walk long distances and climb stairs, and weakness in the arms and hands often leads to an inability to grip or hold on to heavy objects.
In severe cases, weakness may spread to the muscles in the chest that control breathing. This can lead to respiratory distress or failure ("myasthenic crisis"), and the need for assisted ventilation.
Diagnosis of the disease is made via review of the individual's medical history, and physical and neurological examinations. Confirmatory tests may include:
- a blood test that detects the presence of immune system molecules or antibodies that target the acetylcholine receptors;
- the edrophonium test, in which the individual is administered a drug that blocks the breakdown of acetylcholine, temporarily increasing the levels of the protein at the NMJ. In people with MG involving the eye muscles, the drug will temporarily relieve weakness;
- nerve conduction studies, which evaluate muscle fatigue in response to repeated nerve stimulation;
- single fiber electromyography (EMG), in which single muscle fibers are stimulated by electrical impulses to detect impaired nerve-to-muscle transmission;
- computed tomography (CT), which can identify abnormalities in the thymus gland; and
- pulmonary function testing, which measures breathing strength; this exam may help predict respiratory failure that could lead to myasthenic crisis.
There are a number of medications designed to help control MG, and with treatment many experience significant improvement of their muscle weakness. In some cases, MG may go into temporary remission and muscle weakness may disappear, allowing for the discontinuation of medication.
- immune system suppression with drugs such as corticosteroids (prednisone and prednisolone); azathioprine (Imuran); mycophenylate mofetil (CellCept); cyclosporine (Neoral, Sandimmune); and cyclophosphamide (Cytoxan, Neosar);
- medications designed to block the activity of the protein that normally breaks down acetylcholine (an enzyme called acetylcholinesterase) such as pyridostigmine (Mestinon);
- removal of harmful antibodies through plasma exchange, in which an intravenous line removes the antibodies from the blood;
- intravenous immnoglobulin (IVIg) therapy, which involves the injection of nonspecific antibodies as a means to decrease the immune system's own antibody production; and
- removal of the thymus gland ("thymectomy"), which has been shown to produce complete remission in some people with the disease.
People with MG also should be aware that many prescription drugs can worsen their disease. Those with MG should avoid:
- muscle relaxants used during surgery
- aminoglycoside and quinolone antibiotics
- cardiac anti-arrhythmics
- local anesthetics
- magnesium salts (including milk of magnesia)