Myasthenia gravis (MG) is either an autoimmune or congenital neuromuscular disease that leads to fluctuating muscle weakness and fatigue. The name myasthenia gravis, which is Latin and Greek in origin, literally means "grave muscle weakness." With current therapies, however, most cases of myasthenia gravis are not as "grave" as the name implies. In fact, most individuals with myasthenia gravis have a normal life expectancy.
"Additional forms of treatment for Myasthenia Gravis may include, 'Plasmapheresis,' - the exchange of plasma, to modify the person's immune system malfunction."
Myasthenia Gravis Definition
Myasthenia Gravis is a form of chronic autoimmune disorder resulting in progressive skeletal muscle weakness. Myasthenia Gravis affects persons from all ethnic groups and both genders, although it commonly affects young adult women under the age of forty years, and men over the age of sixty. Myasthenia Gravis can affect persons of any age as well. On occasion, the disease can occur in members of the same family, although the disease is not contagious or directly inherited.
Myasthenia Gravis causes rapid fatigue and loss of strength in persons affected which improves once they have rested. In the early stages of the disease, the person's muscles which control their eye movement, chewing, facial expressions, and swallowing may be affected. Left untreated, the disease can affect the muscles the person uses to breath, resulting in acute respiratory failure. Muscles that control the person's limb movements may also be affected.
Children with Neonatal Myasthenia may have acquired immune proteins from their mother who is affected with Myasthenia Gravis. Infants with Neonatal Myasthenia Gravis experience temporary symptoms that commonly disappear within about two or three months after they have been born. Other infants develop Myasthenia Gravis that is indistinguishable from that adults experience; the disease is common in juveniles. On rare occasion, children can show signs of either congenital myasthenic syndrome or congenital myasthenia. Neither of these are autoimmune disorders; they are caused by defective genes which produce proteins in either acetylcholinesterase, or the acetylcholine receptor.
Myasthenia Gravis affects about two out of every one-hundred thousand people. Around eighty-five to ninety-percent of those affected by this disease experience generalized Myasthenia Gravis; characterized by weakness in the legs, trunk and arms. Approximately ten to fifteen-percent experience weakness that only affects the control of their eye movements - referred to as, 'Ocular Myasthenia Gravis.' Other forms of Myasthenia Gravis include Congenital Myasthenia Gravis and Transient Neonatal Myasthenia Gravis. The majority of persons with Myasthenia Gravis do not experience a shorter life expectancy because of the disease.
Myasthenia Gravis Causes
Myasthenia Gravis is caused by a malfunction of the person's immune system, although the causative factor remains unknown. The disease may have a genetic link. Potential causes include a form of genetic defect, resulting in congenital Myasthenia Gravis, and the circulation of maternal antibodies through the placenta, resulting in transient neonatal Myasthenia Gravis. There is a neurotransmitter, referred to as, 'Acetylcholine (ACh),' which is involved in the transmission of information to the person's muscle tissue. In this disease, cells that bind other cells to either neutralize or destroy them destroy acetylcholine receptor sites in areas of the person's muscle tissue that receive nerve impulses, preventing the nerve impulses from reaching the person's muscles. The result is an experience of weakness and rapid fatigue in the muscles affected.
A person's thymus is an organ which produces cells that are involved in immune responses. The thymus is located below the larynx and above the heart. About fifteen-percent of persons with Myasthenia Gravis have a tumor in their thymus, known as a, 'Thymoma,' while sixty to eighty-percent experience an enlargement of the thymus referred to as, 'Hyperplasia.' Persons with Myasthenia Gravis have antibodies that block, alter, or destroy their receptors for acetylcholine at the neuromuscular junction, preventing their muscles from contracting. Persons with Seronegative Myasthenia Gravis have no antibodies at all to receptors for acetylcholine and muscle-specific kinase, something that is involved in cell signaling and information of the neuromuscular junction. A person's immune system usually produces these antibodies; person's with Myasthenia Gravis have an immune system that is attacking itself. Persons with other autoimmune diseases are also at an increased risk of Myasthenia Gravis.
Myasthenia Gravis Symptoms
Among the first symptoms that persons affected by this disease notice are weakness in their eye muscles, trouble swallowing, and difficulty with muscles controlling facial expressions. People often do not recognize symptoms of Myasthenia Gravis immediately. Other people experience difficulty with slurred speech or trouble with breathing; the disease can affect any voluntary muscle. Symptoms of Myasthenia Gravis may also include:
A, 'Myasthenic Crisis,' is a medical emergency which develops when a person's muscles that control their breathing become severely weakened, potentially leading to acute respiratory failure and the need for the use of a respirator in order to assist with breathing. Additional complications might include food aspiration, choking, or pneumonia. Complications can be triggered by illnesses such as a viral respiratory infection, corticosteroid use that is tapered too quickly, surgery, pregnancy, overexertion, or emotional stress, or an adverse reaction to a medication.
Myasthenia Gravis Diagnosis
Diagnosing Myasthenia Gravis begins with a review of the person's medical history, followed by both physical and neurological examinations. A doctor looks for impairment of the person's eye movements, or muscle weakness without any changes in their ability to feel things. If a potential for a diagnosis of Myasthenia Gravis is suspected by the doctor, there are a number of tests that may be performed to confirm a diagnosis.
Blood testing may detect immune molecules or acetylcholine receptor antibodies in the person's bloodstream. The majority of persons with Myasthenia Gravis present abnormally high levels of these antibodies in their blood. Persons with ocular forms of the disease may not present antibodies in their bloodstream that are detectable by these tests.
An, 'Edrophonium Test,' involves administration of intravenous edrophonium chloride, or, 'Tensilon,' a medication that blocks degradation of acetylcholine while temporarily increasing levels of acetycholine at the neuromuscular junction. In persons with Myasthenia Gravis who experience eye muscle involvement, edrophonium chloride briefly relieves weakness. Another method of confirming a diagnosis of Myasthenia Gravis involves a version of nerve conduction study, during which tests for specific muscle fatigue through repetitive nerve stimulation are performed. The tests record weakening muscle responses when nerves are repetitively stimulated, with the goal of demonstrating decrements of the person's muscle action potential caused by impaired nerve-to-muscle transmission.
Another form of test that may be used to confirm a diagnosis of Myasthenia Gravis is called the, 'Single Fiber Electromyography (EMG),' test. The EMG tests single muscle fibers by stimulating them with electrical impulses, potentially detecting impaired nerve-to-muscle transmission. The EMG tests measures the electrical potential of the person's muscle cells. Persons with Myasthenia Gravis have muscle fibers that do not respond as well to repetitive electrical stimulation as the muscles of person's who are not affected by the disease.
A CT scan can be used to identify abnormalities in a person's thymus gland, including the presence of a Thymoma. There is also an examination referred to as, 'Pulmonary Function Testing,' that measures a person's breathing strength that may be ordered. The test assists in predicting whether the person being tested has respiration that could fail, leading to a Myasthenic Crisis.
Many times, a delay in receiving a diagnosis of Myasthenia Gravis of one or two years is not unusual. Weakness is a symptom of several other disorders; a diagnosis of Myasthenia Gravis is often missed in persons with mild weakness, or in persons who experience weakness in only a few muscles. The process of diagnosing this disease can take time.
Myasthenia Gravis Treatment
When it comes to neuromuscular disorders, Myasthenia Gravis is one of the most treatable ones. Treatment of the disease depends on a number of factors, to include the person's overall health, their age, the severity of the disease, and the rate at which it is progressing. There are a number of medications that can be used to treat Myasthenia Gravis. These medications include:
Anticholinesterase Medications: Neostigmine, Pyridotigmine - prevent ACh destruction while increasing accumulation of ACh at neuromuscular junctions, improving the ability of muscles to contract.
Corticosteroids: Prednisone - suppresses antibodies that block AChR at the neuromuscular junction. May be used with Anticholinesterase. Corticosteroids can improve the person's symptoms within a few weeks. Once the person's symptoms stabilize, the dose is gradually decreased.
Immuno-suppressants: Azathioprine, Cyclophosphamide - used to treat generalized Myasthenia Gravis if other medications fail to relieve symptoms. These medications may cause severe side-effects such as a low white blood cell count, nausea, liver dysfunction, vomiting, and hair loss. Immuno-suppressants are not used to treat congenital Myasthenia Gravis because this form of the disease is not the result of an immune system malfunction.
Additional forms of treatment for Myasthenia Gravis may include, 'Plasmapheresis,' - the exchange of plasma, to modify the person's immune system malfunction. Plasmapheresis can be used to treat a severe worsening of symptoms that is experienced by the person affected, as well as in preparation for surgery such as a Thymectomy, which involves removal of the person's thyroid. During Plasmapherisis, the person's blood is removed from their body and their blood cells are separated from the liquid portion of their blood. The AChR antibodies are removed, their blood cells are diluted with artificial plasma, and infused back into their body. Commonly, two to three liters of plasma is removed and replaced during treatment, requiring several hours of time. The majority of person's receiving Plasmapheresis undergo a number of sessions over a period of two or more weeks, improving the symptoms they experience in association with Myasthenia Gravis for six to eight weeks. The risks involved with this procedure include dizziness, low blood pressure, blurred vision, as well as the potential for the formation of blood clots.
A, 'Thymectomy,' is a surgical procedure involving the removal of the person's thymus gland with the goal of reducing symptoms of Myasthenia Gravis. In more than seventy-percent of persons without thymoma the procedure may cure the individual, as well as potentially re-balancing their immune system.
Persons with a diagnosis of Myasthenia Gravis who receive treatment for the disease can expect significant improvement related to symptoms of muscle weakness, as well as expecting to lead productive lives. Some person's with Myasthenia Gravis experience temporary remission of the disease, with muscle weakness that disappears completely to the point where medications may be discontinued. The goal of surgical thymectomy is long-lasting and complete remission.
Teal is the color designated to Myasthenia Gravis Awareness, and June is National Myasthenia Gravis Awareness Month. During the month of June, MGFA's official MG Awareness Month, the national office, as well as chapters and individuals throughout the country, are involved in a variety of activities to promote awareness.
Within the U.S. Federal government, the National Institute of Neurological Disorders and Stroke (NINDS), one of the National Institutes of Health (NIH), has primary responsibility for conducting and supporting research on brain and nervous system disorders, including myasthenia gravis.
Much has been learned about myasthenia gravis in recent years. Technological advances have led to more timely and accurate diagnosis, and new and enhanced therapies have improved management of the disorder. There is a greater understanding about the structure and function of the neuromuscular junction, the fundamental aspects of the thymus gland and of autoimmunity, and the disorder itself. Despite these advances, however, there is still much to learn. Researchers are seeking to learn what causes the autoimmune response in myasthenia gravis, and to better define the relationship between the thymus gland and myasthenia gravis.
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