011 Myasthenia Gravis 2012

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The fact sheets have been adapted from material originally prepared by MDA USA with their kind permission. We are grateful for providing this valuable and informative material Facts About Myasthenia Gravis Myasthenia Gravis (MG), Lambert-Eaton Myasthenic Syndrome (LES) & Congenital Myasthenic Syndrome (CMS) What is Myasthenia Gravis? Myasthenia gravis (MG) causes weakness that gets worse with exertion and improves with rest. The disease first appeared in medical reports in 1672, but didn’t ear
    1   The fact sheets have been adapted from material srcinally prepared by MDA USA with their kind permission. We are grateful for providing this valuable and informative material Facts About Myasthenia Gravis Myasthenia Gravis (MG), Lambert-Eaton Myasthenic Syndrome (LES) & Congenital Myasthenic Syndrome (CMS) What is Myasthenia Gravis? Myasthenia gravis (MG)  causes weakness that gets worse with exertion and improves with rest. The disease first appeared in medical reports in 1672, but didn’t earn its name, which literally means grave muscular weakness, until the 1880s. Physicians in 19th-century Germany, the first to begin systematic studies of the disease, noted that it produces weakness that fluctuates but generally progresses with time. Lacking crucial insights into the properties of nerve and muscle, they weren’t able to do much for their patients, many of whom lost strength rapidly and eventually died from respiratory failure. Even in the early 20th century, the mortality rate of MG was around 70 percent. Fortunately, over the past 100 years, the srcins of MG have gradually unfolded, and the outlook for people with the disease has improved dramatically. MG is an autoimmune disease —  a disease that occurs when the immune system attacks the body’s own tissues. In MG, that attack interrupts the connection between nerve and muscle —  the neuromuscular junction . Muscles that control the eyes, face, neck, and limbs are commonly affected. Thanks to this understanding of the mechanism behind MG, physicians can now treat it with drugs that suppress the immune system or boost the signals between nerve and muscle. Surgeries and other procedures are also helpful in many cases. Physicians now estimate, that when MG is properly treated, the mortality rate is near zero. Most people with the disease are able to manage their symptoms and lead active lives, and a few experience remission lasting many years. This fact sheet provides essential information about MG and two related diseases that affect the neuromuscular junction,  Lambert-Eaton myasthenic syndrome (LEMS)  and congenital myasthenic syndrome (CMS) .  What causes MG? The immune system normally defends the body against diseases, but sometimes it can turn against the body, leading to an autoimmune disease. (See diagram on right) MG is  just one of many autoimmune diseases, which include arthritis and type I diabetes. In all of these diseases, an army of immune cells that would normally attack bacteria and disease-causing germs mistakenly attacks cells and/or proteins that have essential functions in the body. In most cases of MG, the immune system targets the acetylcholine receptor    —   a protein on muscle cells that’s required for muscle contraction. (See diagram below.) In myasthenia gravis, muscle weakness often first appears in the muscles of the face, neck and jaw. The arm and leg muscles are affected later. Normally (A), the immune system releases antibodies to attack foreign invaders, such as bacteria. In autoimmune diseases (B), the antibodies mistakenly attack a person’s own tissues. In myasthenia gravis, they attack and damage muscle cells; in Lambert-Eaton myasthenic syndrome, they attack nerve cells that send messages to muscle.    2   Neuromuscular Junction  At the normal neuromuscular junction, a nerve cell tells a muscle cell to contract by releasing the chemical acetylcholine (ACh).  ACh attaches to the ACh receptor —  a pore or channel in the surface of the muscle cell —  twisting it open and allowing an inward flux of electrical current that triggers muscle contraction. These contractions enable someone to move a hand, to dial the telephone, walk through a door or complete any other voluntary movement.  About 85 percent of people with MG have antibodies  against the ACh receptor in their blood. The antibodies (Yshaped missiles that immune cells called B-cells  use to attack bacteria and viruses) target and destroy many of the ACh receptors on muscle. Consequently, the muscle’s response to repeated nerve signals declines with time, and the muscles become weak and tired.  About 15 percent of people with MG are seronegative  for antibodies to the ACh receptor, meaning the antibodies aren’t detectable in their blood (serum). Recently, it’s been discovered that a large fraction of these people have antibodies to muscle-specific kinase (MuSK) , a protein that helps organize ACh receptors on the muscle cell surface. Scientists don’t know what triggers most autoimmune reactions, but they have a few theories. One possibility is that certain viral or bacterial proteins mimic self-proteins in the body (such as the ACh receptor), stimulating the immune system to unwittingly attack the self-protein. There's also evidence that an immune system gland called the thymus  plays a role in MG. (See illustration below) Located in the chest just below the throat, the thymus is essential to the development of the immune system. From fetal life through childhood, the gland teaches immune cells called T-cells  to recognize self from non-self.  About 15 percent of people with MG have a thymic tumor, called a thymoma , and another 65 percent have overactive thymic cells, a condition called thymic hyperplasia.   When the thymus doesn’t work properly, the T -cells might lose some of their ability to distinguish self from non- self, making them more likely to attack the body’s own cells. Who gets MG? MG affects two to seven out of every 10,000 people in Western countries. It occurs about one and a half times more often in women than in men. The disease can appear at any age, but the average age of onset in females is 28; in males, it’s 42. In about 10 percent of cases, MG begins in childhood (  juvenile onset  ). Genetic susceptibility appears to play a role in MG and in other autoimmune diseases. Most studies suggest that if you have a relative with an autoimmune disease, your risk of getting an autoimmune disease is increased —  the closer the relative, the higher the risk. Even for identical twins, however, that risk is relatively small. Most studies suggest that when one twin has an autoimmune disease, the other has less than a 50 percent chance of getting the same disease.  Also, people who already have one autoimmune disease have a greater risk of developing another one. It’s estimate d that 5 percent to 10 percent of people with MG Myasthenia gravis occurs when the immune system makes antibodies that destroy the ACh receptor (AChR), a docking site for the nerve chemical acetylcholine (ACh). Some treatments block acetylcholinesterase (AChE), an enzyme that breaks down ACh, while others target the immune system. The thymus, a small gland in the upper chest, seems to play a role in myasthenia gravis.    3  have another autoimmune disease, which appeared before or after the onset of MG. The most common of these are autoimmune thyroid disease, rheumatoid arthritis and systemic lupus erythematosus (SLE, a disease that affects multiple organs). What happens to someone with MG? Weakness and Fatigue MG weakens and fatigues the body’s voluntary muscles  (those we can move at will). It doesn’t damage the musculature of the heart or the gastrointestinal tract. Early in its course, MG tends to affect the muscles that control movement of the eyes and eyelids, causing ocular weakness. Consequently, a partial paralysis of eye movements (ophthalmoparesis),  double vision ( diplopia ), and droopy eyelids (ptosis) are usually among the first symptoms of MG. Weakness and fatigue in the neck and jaw also can occur early in MG. This bulbar   weakness —  named for the nerves that srcinate from the bulblike part of the brainstem —  can make it difficult to talk, chew, swallow and hold up the head. Bulbar weakness tends to give speech a slurred, nasal quality. It can also lead to frequent choking spells, and make eating unpleasant and tiresome. In generalized MG,  weakness tends to spread sequentially from the face and neck to the upper limbs, the hands and then the lower limbs. It may become difficult to lift the arms over the head, rise from a sitting position, walk long distances, climb stairs or grip heavy objects. In severe cases, weakness may spread to muscles in the chest that control breathing. Disease Course Weakness and fatigue in MG tend to fluctuate from day to day, and even during a single day. People with the disease are often strongest in the morning after a full night’s sleep and weakest in the evening. Over a longer term, the symptoms of MG usually progress, reaching maximum or near-maximum severity within one to three years of onset in most people. In about 15 percent of people, the disease remains ocular, but in most, it becomes oculobulbar or generalized. If the disea se remains ocular for three years, it usually doesn’t become generalized. Weakness serious enough to require a wheelchair is almost unheard of in MG. Most people, when properly treated, find they can remain physically active. Remission , a reversal of some or all symptoms, occurs in about 20 percent of people with MG. Usually, the remissions are temporary, with an average duration of five years, but some people experience more than one remission during their lifetimes. A few people have experienced apparently permanent remissions, lasting over 20 years. Compared to adult-onset   MG,  juvenile MG tends to progress more slowly and has a higher incidence of  remission. Historically, many children given diagnoses of juvenile MG turned out to have a congenital myasthenic syndrome. Early in its course, MG affects the muscles that control eye movement, and droopy eyelids are often among the first symptoms. Juvenile MG progresses more slowly than the adult form, and more often goes into remission.    4   Drugs and Other Concerns Many prescription drugs can unmask or worsen symptoms of MG. These include: ã  muscle relaxants used during surgery ã  aminoglycoside and quinolone antibiotics ã  cardiac anti-arrhythmics ã  local anaesthetics ã  magnesium salts (including milk of magnesia) When taking a new prescription drug for the first time, it’s a good idea to consult your doctor about its possible effects on MG. Also, you might want to keep a Medic Alert bracelet or card handy to inform emergency medical personnel that you have MG and that certain drugs can be harmful to you. Overexertion, emotional stress, infections (from tooth abscesses to the flu), menstruation and pregnancy can also lead to increased weakness in MG. (see below) Myasthenic Crisis Especially in people with bulbar or respiratory symptoms, MG can sometimes worsen to the point of myasthenic crisis , an extreme episode of weakness that culminates in respiratory failure and the need for mechanical ventilation. In some cases, the respiratory muscles themselves give out, and in others, weakness in the throat muscles causes the airway to collapse. When MG is properly treated, crisis is very rare. And when crisis does occur, it has a good rate of recovery, thanks to the wide range of treatments for MG and the quality of respiratory care at most hospitals. Sometimes, myasthenic crisis can occur without warning, but it often has an identifiable trigger, such as fever, respiratory infection, traumatic injury, stress, or one of the drug types mentioned. If you have MG, you should have these conditions monitored by a physician, and if you experience labored breathing or unusual weakness, you should seek immediate medical attention. Pregnancy In rare cases, pregnancy appears to trigger the onset of MG. In women who already have MG, pregnancy can cause a worsening of symptoms (usually after birth, but sometimes during the first trimester); an improvement (usually during the first trimester); or no change, with about equal likelihood. These trends aren’t consistent from one pregnancy to the next. Some medications for MG (see How Is MG Treated? ) are safe to use during pregnancy and nursing, but some others aren’t recommended. If you’re planning to become pregnant, you should consult your physician, and if you’re a n ursing mother, consult your child’s pediatrician. Between 10 percent and 20 percent of babies born to mothers with MG develop transient neonatal MG,  probably because the antibodies that cause MG can pass through the placenta. Symptoms (such as feeble cry, feeding difficulties or respiratory weakness) are often detected within hours to days after birth, and decreased movement may be detected inside the womb. Pregnancy can worsen a woman’s symptoms of MG, and her child may be born with transient neonatal MG —  a temporary condition.
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