Myasthenia Gravis Tests

Myasthenia gravis (MG) tests are used to diagnose MG, a chronic (long-lasting) autoimmune disease that causes weakness in muscles throughout your body. In autoimmune diseases, your immune system mistakenly attacks the healthy cells of your organs and tissues. If you have MG, your immune system makes antibodies that block or change the connection between your nerves and muscles.

MG causes weakness in the voluntary muscles in your body. These are muscles that you can control. The symptoms of MG may begin suddenly.

There are different types: Ocular MG affects the muscles controlling the eyelids. These are often the first and sometimes the only muscles that MG affects.; In generalized MG, the weakness may also be in your eyelids. But it affects other muscles as well, such as those that control eye movement and those in your neck, arms, and/or legs.

If the muscles that control your breathing are affected, this is called a myasthenic crisis. It is a life-threatening emergency.; Researchers aren't sure why people get MG. It is not inherited (passed down in families).

But occasionally, the disease affects more than one member of the same family. What is known is that you may have an increased chance of developing MG if you: Have another autoimmune disorder, such as rheumatoid arthritis or systemic lupus erythematosus.; Have a problem with your thymus gland, a small organ in your upper chest. It is part of your immune system.

If you have MG, your thymus gland might be larger than usual, or you may have a thymoma (thymus tumor). These tumors are usually benign (not cancer), but they can become cancerous.; Are a woman under age 40 or a man over age 60. This is the age range MG most commonly affects (although you can develop it at any age).; MG testing can help you get diagnosed and treated for the disease.

While there is no cure for MG, there are treatments that can relieve symptoms and may even allow you to have periods without any symptoms (remission).

Why this test is done

You may need to be tested if you have symptoms of MG. Your symptoms will depend on which muscles are affected. The symptoms often include:

• Drooping of one or both eyelids
• Weakness of the eye muscles
• Blurred or double vision
• Changes in facial expression
• Weakness in arms, hands, fingers, legs, and/or neck
• Trouble swallowing and/or chewing
• Trouble talking
• Fatigue
• Shortness of breath

MG symptoms usually get worse after periods of activity, such as exercise, and improve after rest.

How to prepare

You don't need any special preparations for a neurological exam, ice pack test, or antibody test.

For the other tests, you may need to fast (not eat or drink) or avoid certain foods and beverages before the test. Tell your provider if you are pregnant, have pieces of metal in your body, or if you have a pacemaker or cardiac defibrillator. Special steps may need to be taken before the test.

Also, tell your provider if you take any medicines. If you're taking blood thinners, you may need to watch for more bleeding from the needle.

Your provider will let you know if you need to make any additional preparations.

Sample type

Blood

Other names for this test

Ice pack test, edrophonium test, tensilon test, nerve conduction study