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About Myasthenia Gravis

Poor communication can cause all manner of trouble. That’s true not only between people, but even in a single person’s body. When the parts of the muscles responsible for receiving nerve impulses are mistaken by the immune system for disease and destroyed, the nerves can no longer properly communicate with the muscles, and voluntary muscle movements are affected, resulting in a condition called myasthenia gravis. Myasthenia gravis affects about one in 5,000 people. It can strike anyone at any time, but initial onset is most common people between the ages of 50 and 70 and in in women under 40.

It’s not always clear what causes the immune system to attack the muscles. Myasthenia gravis is one of the few autoimmune diseases that does not appear to have a genetic component, but there is probably an inborn predisposition that, in combination with environmental triggers, leads to the condition. People who take certain medications—some types of antibiotics, beta blockers, quinine, or some others—are more likely to develop the condition. Other risk factors involve the thymus gland, where immune antibodies are produced. Occasionally, myasthenia gravis patients have a non-cancerous tumor in the thymus gland. More often, an enlarged thymus exhibits excess activity, producing the undesired antibodies.

Because myasthenia gravis affects the brain’s ability to send impulses to the muscles, it interferes with voluntary muscle movements, though autonomous activity such as the heart beating remain unaffected. That means difficulty taking a breath or speaking—speech becomes soft or hoarse—trouble chewing or swallowing, facial muscle paralysis, double vision and problems looking people in the eye, and a feeling of having to work harder than usual to move, stand from a chair, or climb up stairs. Another symptoms is a diminished sense of smell, even though this doesn’t involve the muscles.

Fortunately, myasthenia gravis generally is easily treated. When there is a tumor involved, removing the tumor, or even all or part of the gland itself, generally clears up the condition. When there is not, a common approach is to flood the body with the neurotransmitter that relays the signal to the muscles, o compensate for the damage to the receptor sites. As with many autoimmune diseases, drugs that suppress the activity of the immune system alleviate the condition.

Cause Of Myasthenia Gravis

About 60,000 Americans suffer the chronic neuromuscular disorder myasthenia gravis, an autoimmune disorder in which the immune system attacks the pathways nerve impulses travel to reach the muscles, weakening them. The impulses are ordinarily carried by a chemical called acetylcholine. Muscle fibers have acetylcholine receptors, areas where the chemical is detected and processed so that the muscle contracts. However, when a patient has myasthenia gravis, the immune system treats these receptor sites as foreign invaders, creating antibodies that can destroy as much as 80 percent of the sites.

When this happens, most commonly in men over 60 and women under 40, it can cause difficulty breathing, soft speech or hoarseness, trouble chewing or swallowing, facial muscle paralysis, double vision, problems looking people in the eye, and a feeling of having to work harder than usual to move, stand from a chair, or climb up steps. An unusual symptom that appears in many cases is diminished olfactory sensitivity—patients lose some ability to smell, and therefore also to taste food. This is an interesting sign because myasthenia gravis does not appear to cause cognitive impairment, but the sense of smell is not connected to the muscles in any obvious way.

Myasthenia gravis is a rare example of an autoimmune disease that isn’t hereditary. In some cases, it’s caused by an overactive thymus gland—which plays a major role in immune system regulation—resulting from a non-cancerous tumor, but explanations for the remainder of cases are still emerging. Recently, scientists found an antibody to a neurotransmitter that appears to be responsible for a significant proportion of cases.

Myasthenia gravis generally responds well to treatment. As with many autoimmune diseases, immune-system suppressing drugs are the most common treatment approach, though anti-inflammatory drugs are not used, because inflammation is not the problem. Another treatment approach is medication to boost the activity of the neurotransmitter, to compensate for the damage to the receptors. Patients undergoing an attack, called a myasthenic crisis, are given treatments that operate directly on the antibodies responsible; these treatments last a few weeks. In severe cases, such as when there is a tumor, the entire thymus gland is surgically removed.

Myasthenia Gravis And Scent

People with the autoimmune disease myasthenia gravis tend to develop an unusual symptom: they lose the sense of smell. This may not sound so bad when the septic tank overflows, but the condition, called anosmia, can have serious consequences. How food tastes is closely tied to how it smells, meaning people with anosmia don’t get the full taste of food; this lack of a psychological reward for eating can result in poor appetite and malnourishment. Moreover, the nose can act as a sentry for the body, with spoiled food and harmful microbes having foul odors that stimulate an immune response.

Researchers gave a standard scent identification test to patients with myasthenia gravis, patients with a similar disorder called polmyositis, and healthy subjects. These subjects were also given a picture recognition test, in order to distinguish problems identifying smells in particular from more general recognition problems—the researchers wanted to rule out overall cognitive impairment, though that’s not generally a symptom of myasthenia gravis.

What they found was that people with myasthenia gravis have significantly reduced ability to smell things—and this held regardless of severity, duration, or even having or not having a history of smoking. In severe cases, myasthenia gravis is treated by removal of the thymus gland, which develops a tumor in about one in every seven cases of the disease, and this surgery has no effect on the olfactory dysfunction.

Other symptoms of the condition, in which nerves and muscles don’t communicate properly, causing fatigue and weakness, include drooping eyelids, double vision, problems chewing or swallowing, difficulty with speech or facial expressions, weakness in your arms, and neck muscle problems that make it difficult to hold your head up. Myasthenia gravis is an autoimmune disease, in which the body attacks receptor sites for the neurotransmitters that carry messages from the brain to the muscles.

One of the most common first-line treatments focuses on increasing the number of those neurotransmitters, so that even with some of the receptors gone, the signal can still get through. Another option often used is suppressing the immune system, protecting the receptor sites. Recent research has looked at the possibility of modifying only the immune response to those sites, rather than throughout the body, reducing side effects.

Your Thymus Gland And You

The thymus gland is a small organ, part of the endocrine system, at the back of the sternum, between the lungs. It gets smaller with age, and is gradually replaces with adipose tissue. When it is working properly, it creates and trains immune cells, though fewer and more slowly as more and more of the original tissue gets replaced.

It was named for the herb thyme, which ancient doctors thought the organ resembled. however, it was believed to be only a repository of dead immune cells until 1961, when the gland’s function was discovered. Because of the role of the thymus in the immune response, these antibodies are called T-lymphocytes.

The T-lymphocytes are the part of the immune system that directly attack intruders. These cells identify their targets by their proteins. The thymus is responsible for eliminating the T-lymphocytes that are programmed to go after the body’s own cells. It produces the same protein patterns as the body’s organs and eliminates antibodies that respond.

Dysfunction in the thymus can result in one of a small number of autoimmune diseases, of which myasthenia gravis is by far the most common. It is believed that myasthenia results from abnormal or excessive growth of the thymus, which leads to the production of too many T-lymphocytes. A small number of myasthenia cases are caused by a thymoma, a usually benign tumor on the thymus. In these cases, removal of the tumor, or even the entire gland, may be necessary.

Although the exact mechanism by which thymus activity leads to myasthenia is unknown, scientists have some clues. One common hypothesis is that the thymus gives erroneous instructions to the T-lymphocytes. The myoid cells in the thymus that are supposed to catch T-lymphocytes that target muscles are misaligned, causing the antibodies to think the acetylcholine receptor sites they attack are invading foreign cells. As a result, the T-lymphocytes attack the receptors, destroying as many as 80 percent of them throughout the body and rendering the muscles unable to respond to neural signals.

Research is ongoing into the role of the thymus in myasthenia gravis and what this might mean for treatment. If the exact link can be determined, doctors may be able to treat the condition with minimal side effects.

Pregnancy and Myasthenia

Unusually for autoimmune diseases, there is no evidence that myasthenia gravis is typically inherited. However, pregnant women—and women who are considering becoming pregnant—who have the condition need to be aware of the risks, both to themselves and to their fetuses. Women under 40, who are in their childbearing years, are particularly at risk for myasthenia gravis.

About one in three pregnant women with myasthenia gravis report their symptoms getting worse, mostly in the first trimester. In some women, it heightens the risk of myasthenic crisis, a dangerous condition in which the pulmonary muscles are too weak for the patient to continue breathing. It is difficult to predict how pregnancy will affect the course of the disease in a particular patient, however; in some cases, in fact, women experience a remission, and are symptom-free during pregnancy. Most women have few myasthenia symptoms in the second and third trimesters.

Preeclampsia—a condition in which a pregnant woman has high blood pressure and protein in the urine, and which often results in induced labor and premature delivery—is more common in expectant mothers with autoimmune diseases, including myasthenia. The most common treatment for preeclampsia is magnesium sulphate used to induce labor, but it is unsafe for myasthenia patients; if it develops into seizures, the drug Dilantin is used.

Pregnant women may need to avoid the medications used for myasthenia. Immunosuppressants can be particularly dangerous for a developing fetus. While another type of medication called cholinesterase inhibitors are usually safe, when taken intravenously, these drugs can cause premature labor. On the other hand, corticosteroids such as prednisone are believed to be safe for mother and fetus alike.

In about one case in five, the baby will be born with neonatal myasthenia gravis. This is not inherited, but comes from the mother’s antibodies being transferred through the placenta. It varies in severity from infant to infant, but it can be safely treated with cholinesterase inhibitors and usually goes away within a few weeks. In other cases, these antibodies affected fetal movement, leading to a rare joint deformity disorder called arthrogryposis. This does not affect cognitive function, however, nor does it get worse over time.

If you are pregnant, or want to be, and have myasthenia, be sure to let you OB/GYN know. They can work with you to help keep you and your baby safe and healthy.

Testing And Treatment For Myasthenia

It is estimated that myasthenia gravis patients are all to often diagnosed as many as two years after the onset of symptoms. That’s because those symptoms, primarily weakness and fatigue, are common.

Diagnosing the disease is, in fact, a multi-step process. It starts with a look at your medical history and some physical examinations. At this point, the doctor is looking for eye or muscle problems that suggest myasthenia. For example, you may be asked to look upwards for a long time. In patients with myasthenia, this will induce a condition called ptosis, or drooping of the eyelids. Another approach is to test muscle strength after a repetitive task and then again after a period of rest.

Confirming the diagnosis is done in several ways. A blood test may be used to look for chemicals associated with the condition. Myasthenia is an autoimmune disease, in which the body produces antibodies that attack its own tissue. Blood tests look for two of those antibodies; 85 percent of myasthenia patients have acetylcholine-receptor antibodies, and many of the rest have muscle-specific tyrosine kinase, or MuSK, antibodies. These antibodies respectively attack the sites on the muscles that receive signals from the brain and the mechanism that transfers those signals from the nerve fibers.

Another procedure involves injecting a chemical called edrophonium that counteracts the immune response that causes myasthenia, though for too short a time to make it a practical treatment. If it does produce brief improvement, however, that is a strong indicator of myasthenia.

Once diagnosed, there are several treatment options available. Myasthenia has no cure, but medication and lifestyle changes can be used together to help reduce symptoms and improve a patient’s quality of life.

Patients need to take the effects of the disease into account, for instance by eating when they are well rested, and having more and smaller meals, to avoid problems chewing and swallowing. Railings can be installed in someone’s home to help provide support. An eye patch can alleviate double vision.

In addition to these workarounds, medications can help minimize symptoms. Immunosuppressants stop antibodies from attacking healthy tissue. Drugs called cholinesterase inhibitors boost the signal to the muscles that is diminished by myasthenia. You doctor can tell you about other treatment options and help you determine which is best for you.

Recognizing Myasthenia Gravis

The neuromuscular disease myasthenia gravis is often difficult to diagnose. It can take up to two years after its effects start to appear before doctors can get a handle on what is going on.

Myasthenia can affect any muscle in the body that you can voluntarily control, but the most common symptoms are:

  • Weakness in the muscles of the chest wall, which can make breathing difficult
  • Soft or nasal speech, or having to struggle, physically, to speak
  • Unexplained hoarseness or changes in the voice
  • Droopy eyelids, double vision, or problems maintaining a steady gaze
  • Weakness or paralysis of the muscles in the face, and a markedly curtailed range of facial expressions
  • Difficulty chewing or swallowing, and frequent drooling, gagging or choking
  • Unexplained fatigue and a feeling of having to work extra hard to move
  • Trouble lifting your head and facing forward rather than down
  • Sudden inability to lift things, stand up from a chair, or climb stairs

Symptoms of myasthenia gravis often improve after a rest, but they tend to get steadily worse over time. The difficult breathing can be life threatening.

If you develop double vision, you have trouble chewing or swallowing, you find your eyelid drooping, or you experience intermittent muscle weakness, contact a doctor. These are the most obvious signs of myasthenia gravis, and a doctor can help you create a treatment strategy.