Myasthenia gravis is a relatively uncommon disease, with a prevalence of about 14 cases per , 1,2 MG can occur at any age; the data presents a peak among females in their second decade of life and older males in their sixth to eighth decades. MG causes weakness in muscles that control the eyes, face, neck, and limbs. Symptoms include partial paralysis of eye movements, double vision and droopy eyelids, as well as weakness and fatigue in neck and jaws with problems chewing, swallowing, and holding up the head.
The hallmark of the disorder is a fluctuating degree and variable combination of weakness in ocular, bulbar, limb, and respiratory muscles.
These symptoms may not always present and may shift from mild to severe repeatedly. The fluctuation of symptoms is an important feature that helps neurologists to distinguish MG from other disorders. Eventually, the diagnosis of MG can be established both by clinical and serologic testing See Diagnosis. For more, see Signs and Symptoms. The cause of MG is unclear.
Researchers suspect viruses or bacteria might trigger the autoimmune response; the thymus gland also seems to sometimes play a role in the disease. Resection of the thymus, chemotherapy, and radiation therapy are likely to be recommended by the physician.
Screening for thyroid abnormalities should be part of the initial evaluation. Although MG is not hereditary, genetic susceptibility appears to play a role in it and other autoimmune diseases.
MG is treatable 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.
Most people with the disease are able to manage their symptoms and lead active lives, and a few experience remissions lasting many years. Research Clinical Trials Journal Articles.
Resources Reference Desk Find an Expert. Causes of muscle disorders include Injury or overuse, such as sprains or strains , cramps or tendinitis A genetic disorder, such as muscular dystrophy Some cancers Inflammation, such as myositis Diseases of nerves that affect muscles Infections Certain medicines Sometimes the cause of muscle disorders is unknown.
Start Here. Diagnosis and Tests. Treatments and Therapies. Related Issues. Normally, at the neuromuscular junction, when your brain sends electrical signals or impulses down a motor nerve, the nerve endings release a neurotransmitter called acetylcholine , which attaches, or binds, to sites in your muscles called acetylcholine receptors. This activates the muscle and causes a muscle contraction. In people with myasthenia gravis, however, antibodies proteins produced by your immune system to fight off infection block, alter, or destroy the receptors for acetylcholine at the neuromuscular junction, which prevents the muscle from contracting.
This is typically caused by antibodies to the acetylcholine receptor. In addition, antibodies to a protein called muscle-specific kinase MuSK may also disrupt transmission at the neuromuscular junction. Researchers also think that a part of your immune system called the thymus gland , situated in the upper chest beneath your breastbone, may trigger or maintain the production of the antibodies that block the neurotransmitter acetylcholine.
While the thymus is small in healthy adults, it's abnormally large in some adults with myasthenia gravis. In addition, tumors which usually aren't cancerous may be present in the thymus glands of people with myasthenia gravis, affecting antibody production. These tumors are called thymomas. The role of antibodies and the thymus gland in myasthenia gravis in some people is what makes the condition an autoimmune disorder — meaning that the immune system mistakenly attacks itself.
In these cases, antibodies against another protein, lipoprotein-related protein 4, play a part in the development of the condition. In addition, in rare instances, mothers with myasthenia gravis have children who are born with the condition because they pass antibodies blocking acetylcholine or MuSK to the fetus in the womb.
This is called neonatal myasthenia gravis. However, if the condition is diagnosed and treated promptly, these children generally recover within two months of their birth. Some children may also be born with a rare form of myasthenia gravis called congenital myasthenic syndrome. The condition is extremely rare, and unlike myasthenia gravis, congenital myasthenic syndrome is not an autoimmune disease. Like people with myasthenia gravis, children with congenital myasthenic syndrome experience muscle weakness myasthenia that worsens with physical activity.
This typically begins in early childhood but can also appear in adolescence or adulthood. The muscles in the face, including those that control the eyelids, move the eyes, and enable chewing and swallowing, are most commonly affected. However, other skeletal muscles can also be affected.
Because of the muscle weakness caused by congenital myasthenic syndrome, infants may have feeding difficulties and may experience delays in their development of motor skills, including crawling or walking. In August , researchers in Italy described the development of myasthenia gravis in three adults with severe COVID in an article published in the journal Annals of Internal Medicine. The three adults, who ranged in age from 64 to 71, developed their myasthenia gravis symptoms five to seven days after fever related to the new coronavirus first appeared.
None of the three had prior history of neurologic or autoimmune disorders. However, all three were positive for antibodies that block acetylcholine. These antibodies, which have been shown to cause myasthenia gravis, may have been activated by COVID, the researchers say. One of the three developed respiratory failure — either as a result of the virus or myasthenia gravis.
Still, if you have myasthenia gravis, it may place you at increased risk for serious illness from COVID Talk to your doctor about steps you can take to minimize your risk. To determine if you have myasthenia gravis, your doctor will review your symptoms and medical history and give you a physical exam.
Ice Pack Test If you have weakness in your eyelids, your doctor may place an ice-filled bag on your eyelids for a couple of minutes. In people who have myasthenia gravis, the cooling effect of the ice may temporarily improve the function of the eyelid muscles.
Blood Tests If your physical exam suggests myasthenia gravis, your doctor will likely order a blood test designed to detect antibodies to the acetylcholine receptor. And if that blood test is negative, you may be tested for muscle-specific kinase MuSK antibodies or other, less common antibodies. Repetitive Nerve Stimulation In this test, electrodes are attached to your skin over the muscles to be tested, and small pulses of electricity are used to measure the nerve's ability to send a signal to your muscle.
Your doctor will test the nerve several times to see if its ability to send signals worsens with fatigue. This test may be uncomfortable.
Single-Fiber Electromyography EMG Electromyography measures the electrical activity traveling between your brain and your muscle through a fine wire electrode inserted through your skin and into a muscle. This test may also be uncomfortable. Imaging Scans Your doctor may order a computed tomography CT scan or a magnetic resonance imaging MRI scan to see whether there's a tumor in your thymus.
Pulmonary Function Tests To determine if and how your condition is affecting your breathing, your doctor may order pulmonary function tests, such as spirometry or plethysmography. In spirometry, you take a deep breath and blow into a mouthpiece. In plethysmography, you sit in an airtight room and breathe into a mouthpiece as instructed by a technician.
In years past, doctors used what was called the edrophonium test, also called the Tensilon test, in which the chemical edrophonium was injected into a vein to see whether muscle strength suddenly yet temporarily improved. Edrophonium blocks the breakdown of acetylcholine. With treatment, most people with myasthenia see significant improvements in their muscle weakness, and they can lead normal or nearly normal lives. Roughly 3 percent of people who develop the condition will die from it, and the risk for death is higher in those diagnosed at age 40 or older as well as those with thymoma.
In fact, some people with the condition may even experience remission — a temporary or permanent absence of symptoms. Their muscle weakness may disappear completely.
In addition, up to 50 percent of people who undergo thymectomy surgery experience stable, long-lasting complete remission. Even if your myasthenia gravis goes into remission, it can still return.
Myasthenia gravis is typically treated by a neurologist, and with treatment, the symptoms of myasthenia gravis can be well controlled. For example, a variety of therapies help to improve muscle weakness.
Several different types of medication are used to treat myasthenia gravis. Anticholinesterase agents such as Mestinon pyridostigmine are designed to help improve communication between nerves and muscles. Possible side effects include gastrointestinal upset, diarrhea, nausea, and excessive salivation and sweating. In addition, corticosteroids such as prednisone improve muscle strength by suppressing the immune system and disrupting production of the antibodies that cause myasthenia gravis.
However, prolonged use of these medications can cause serious side effects, including bone thinning osteoporosis , weight gain, diabetes, and increased risk of some infections.
If your doctor prescribes corticosteroids, you may need to come in for regular visits to be monitored for any of these side effects. Your doctor might also prescribe immunosuppressants. As the name suggests, these drugs — Imuran azathioprine , CellCept mycophenolate mofetil , Neoral cyclosporine , Trexall methotrexate , and Prograf tacrolimus — alter your immune system to limit production of harmful antibodies.
These drugs can take months to work and might be used with corticosteroids. Possible side effects include increased risk of infection and liver or kidney damage.
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