What is myasthenia gravis?
Myasthenia gravis is an autoimmune disease characterized by weakness and rapid fatigue of voluntary muscles. It is caused by a defect in the communication between the nerves and muscles. In myasthenia gravis, the body’s own immune system mistakenly creates antibodies that block the neurotransmitter acetylcholine from crossing the small gap between the nerve ending and the muscle it controls (called the neuromuscular junction).
Myasthenia gravis often affects muscles that control eye and eyelid movement, facial expressions, chewing, talking, and swallowing. However, any voluntary muscle can be affected. Muscle weakness tends to worsen with activity and improve with rest.
Some people with myasthenia gravis may also have a thymoma, a tumor of the thymus gland. Thymomas are usually benign, but can become malignant.
Myasthenia Gravis Symptoms
Usually, the first symptoms of myasthenia gravis to appear involve eye problems. Sometimes, the first symptoms involve face and throat muscles. Muscle weakness can occur in your neck, arms, and legs, but it usually happens along with weakness in other parts of your body, such as your eyes, face, or throat.
Specific symptoms of myasthenia gravis may include:
- Drooping of one or both eyelids (ptosis)
- Blurred or double vision (diplopia)
- Impaired speech (dysarthria)
- Difficulty swallowing
- Difficulty chewing
- Limited facial expressions
- Shortness of breath
- Unstable or waddling gait
- Weakness in arms, hands, fingers, neck, and legs
Please contact a medical professional if you are having the symptoms described above or if you are generally worried about your health.
Myasthenia Gravis Treatments
Although there is no known cure for myasthenia gravis, a variety of treatment options can help relieve symptoms:
- Medications: Cholinesterase inhibitors, such as pyridostigmine (Mestinon) may be used to reduce symptoms by facilitating the activity of acetylcholine at the neuromuscular junction. Corticosteroids or immunosuppressants may be used to reduce the activity of your immune system. Some examples of immunosuppressants include:
- Azothioprine (Imuran)
- Mycofenolate mofetil (CellCept)
- Cyclosporine (Sandimmune)
- Intravenous immunoglobulin (IVIg)
- Infusion Therapies: Plasmapheresis (plasma exchange) is a process similar to dialysis that can filter the antibodies out of your blood that are interrupting signals between nerves and muscles. You may be a candidate if you have either significant symptoms that do not respond to other treatments or if you have severe symptoms involving the muscles that control breathing and swallowing.
- Thymectomy Surgery: A thymectomy, or surgical removal of your thymus gland, may be necessary if you have a thymoma. This may be done through open surgery or a minimally invasive procedure. Thymectomy may reduce symptoms of myasthenia gravis even if you do not have a thymoma. Your doctor will help you determine if you are a good candidate for a thymectomy.
Myasthenia gravis is usually a life-long disease that requires ongoing treatment. However, Myasthenia Gravis treatment is usually quite successful, with some patients achieving remission of the disease.
How common is myasthenia gravis?
The prevalence of myasthenia gravis in the United States is estimated at 14 to 20 cases per 100,000 people.
Who gets myasthenia gravis?
Myasthenia gravis can affect anyone, regardless of age, gender, or ethnicity. However, it is more common in women younger than 40 years old and in men older than 60 years old.
The disease is not inherited, and affects approximately 0.02% of the general population.
How is myasthenia gravis diagnosed?
In addition to reviewing your medical history and conducting a physical examination, your doctor may use several tests to diagnose myasthenia gravis, including:
- Edrophonium (Tensilon) test: This test involves administration of a medication short acting medication that increases the amount of neurotransmitter (acetylcholine) in the neuromuscular junction. As a result, patients with myasthenia gravis show a temporary, but often dramatic improvement in their symptoms.
- Repetitive nerve stimulation: This test uses a small amount of electrical current to stimulate the nerves and records the response in muscles supplied by those nerves. The signals recorded can be interpreted to identify patients with myasthenia gravis.
- Acetylcholine receptor antibodies: This test is performed on a blood sample to identify the antibodies that cause myasthenia gravis. There are several types of antibodies that can be tested for to help diagnose the disease.
- Single fiber EMG: This test is perhaps the most sensitive at picking up mild cases of myasthenia gravis. It involves using a small, fine needle inserted in the muscle to detect signals from muscle fibers.