Tests and diagnosisBy 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:
Your doctor may check your neurological health by testing your:
- Muscle strength
- Muscle tone
- Senses of touch and sight
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:
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.
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.
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.
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