Myasthenia gravis

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Tests and diagnosis

By Mayo Clinic staff

To diagnose your condition, your doctor will review your symptoms and your medical history and conduct a physical examination. Your doctor may conduct several tests, including:

Neurological examination
Your doctor may check your neurological health by testing your:

  • Reflexes
  • Muscle strength
  • Muscle tone
  • Senses of touch and sight
  • Coordination
  • Balance

The key sign that points to the possibility of myasthenia gravis is muscle weakness that improves with rest. Tests to help confirm the diagnosis may include:

Edrophonium test
Injection of the chemical edrophonium chloride (Tensilon) may result in a sudden, although temporary, improvement in your muscle strength. This is an indication that you may have myasthenia gravis.

Edrophonium chloride blocks an enzyme that breaks down acetylcholine, the chemical that transmits signals from your nerve endings to your muscle receptor sites.

Ice pack test
If you have a droopy eyelid, your doctor may conduct an ice pack test. In this test, a doctor places a bag filled with ice on your eyelid. After two minutes, your doctor removes the bag and analyzes your droopy eyelid for signs of improvement. Doctors may conduct this test instead of the edrophonium test.

Blood analysis
A blood test may reveal the presence of abnormal antibodies that disrupt the receptor sites where nerve impulses signal your muscles to move.

Repetitive nerve stimulation
In this nerve conduction study, doctors attach electrodes to your skin over the muscles to be tested. Doctors send small pulses of electricity through the electrodes to measure the nerve's ability to send a signal to your muscle.

To diagnose myasthenia gravis, doctors will test the nerve many times to see if its ability to send signals worsens with fatigue.

Single-fiber electromyography (EMG)
Electromyography (EMG) measures the electrical activity traveling between your brain and your muscle. It involves inserting a fine wire electrode through your skin and into a muscle.

In a single-fiber EMG, doctors test a single muscle fiber. Most people find this test to be uncomfortable.

Imaging scans
Your doctor may order a CT scan or an MRI to check if there's a tumor or other abnormality in your thymus.

Pulmonary function tests
Your doctor may perform pulmonary function tests to evaluate whether your condition is affecting your breathing.

Treatments and drugs Preparing for your appointment
References
  1. Myasthenia gravis fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/myasthenia_gravis/detail_myasthenia_gravis.htm. Accessed Jan. 18, 2013.
  2. Myasthenia gravis. Office of Women's Health. U.S. Department of Health and Human Services. http://www.womenshealth.gov/publications/our-publications/fact-sheet/myasthenia-gravis.cfm. Accessed Feb. 4, 2013.
  3. Bird SJ. Clinical manifestations of myasthenia gravis. http://www.uptodate.com/home. Accessed Jan. 18, 2013.
  4. Allan W. Pathogenesis of myasthenia gravis. http://www.uptodate.com/home. Accessed Feb. 6, 2013.
  5. Bird SJ. Diagnosis of myasthenia gravis. http://www.uptodate.com/home. Accessed Jan. 18, 2013.
  6. Rubin DI. Neurologic manifestations of hyperthyroidism and Graves' disease. http://www.uptodate.com/home. Accessed Feb. 6, 2013.
  7. Rubin DI. Neurologic manifestations of hypothyroidism. http://www.uptodate.com/home. Accessed Feb. 6, 2013.
  8. Bird SJ. Treatment of myasthenia gravis. http://www.uptodate.com/home. Accessed Jan. 18, 2013.
  9. Bodamer OA, et al. Neuromuscular junction disorders in newborns and infants. http://www.uptodate.com/home. Accessed Feb. 7, 2013.
  10. Neurological diagnostic tests and procedures. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/misc/diagnostic_tests.htm. Accessed Jan. 28, 2013.
  11. Bird SJ. Chronic immunomodulating therapies for myasthenia gravis. http://www.uptodate.com/home. Accessed Feb. 7, 2013.
  12. Bird SJ. Thymectomy for myasthenia gravis. http://www.uptodate.com/home. Accessed Feb. 5, 2013.
  13. Limmer KK, et al. Minimally invasive and robotic-assisted thymus reduction. Thoracic Surgery Clinics. 2011;21:69.
  14. Barbara Woodward Lips Patient Education Center. Myasthenia gravis: A guide for patients. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2003.
  15. How can I provide emotional support for a relative who has MG? Myasthenia Gravis Association of America. http://www.myasthenia.org/LivingwithMG/InformationalMaterials.aspx. Accessed Feb. 7, 2013.
  16. U.S. News best hospitals 2012-2013. U.S. News & World Report. http://health.usnews.com/best-hospitals/rankings. Accessed Jan. 25, 2013.
  17. Crum BA (expert opinion). Mayo Clinic, Rochester, Minn. April 1, 2013.
DS00375 April 23, 2013

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