Learn The BasicsSeveral tests can be conducted to diagnose myasthenia gravis (MG).
These include physical and neurological tests, an ice pack test, blood tests, repetitive nerve stimulation and single-fiber electromyography (EMG) tests, imaging tests, an edrophonium (tensilon) test and lung function tests.
Physical and neurological tests
These may include tests for reflexes, muscle strength and tone, coordination, balance and the sense of touch and sight.
Ice pack test
The ice pack test involves placing a pouch filled with ice on the eyelids for a few minutes. This test may be used if a patient has droopy eyelids and their doctor suspects MG.
An improvement in the droopiness may be indicative of MG, as cooling temporarily reverses muscle weakness caused by the disease.
Blood tests
Blood tests to look for antibodies against the acetylcholine receptor (AChR), the hallmark of MG, may help confirm a diagnosis. Around 85% of patients with MG have anti-AChR antibodies in their blood.
However, in rare cases, the disease may be caused by antibodies against other proteins such as muscle-specific kinase (MuSK) or low-density lipoprotein receptor-related protein 4 (LRP4).
Repetitive nerve stimulation and single-fiber EMG tests
During repetitive nerve stimulation, ten electrical pulses are delivered in quick succession, usually to the hand, shoulder or face. This may be more uncomfortable than a standard nerve conduction study. The stimulation is then repeated after a period of rest to look for the effect of fatigue on the muscles. The patient may be asked to exercise the muscle at full force before the stimulation is repeated.
During a single fiber EMG test, a fine needle is inserted into the muscle in several areas around the eyebrow to record the electrical activity and check for any transmission defects in electrical signals from the nerves to the muscles.
Imaging tests
Imaging tests may include a computed tomography (CT) or magnetic resonance imaging (MRI). Here, doctors are looking for signs of an enlarged thymus or a tumor in the thymus, which may be causing MG.
In patients with ocular MG, an MRI of the brain and the orbits (the space in the skull where the eyes are found) may be done to check for any lesions.
Edrophonium (tensilon) test
Edrophonium is a short-acting drug that inhibits the enzyme that breaks down acetylcholine, a chemical that carries electric signals from nerve to muscle cells. An improvement in symptoms like droopy eyelids following edrophonium administration is suggestive of MG.
This test is particularly useful to diagnose ocular MG, in which electrophysiologic tests cannot be performed.
Lung function tests
In some patients with MG, weakness can affect the respiratory muscles and lead to a serious complication called a myasthenic crisis, resulting in respiratory failure.
Respiratory capacity can be assessed using a single breath counting test, which involves the patient inhaling deeply and counting out loudly for as long as possible in a single breath while sitting upright. A count of 25 or less may be a sign of MG worsening.
Lung function tests with spirometry can also be performed to assess the strength of the expiratory muscles, as well as the maximal inspiratory and expiratory pressure, which are usually reduced in MG.
The rate and function of a patient’s breathing, oxygenation and time trends may also be evaluated.
Reviewed by Debjyoti Talukdar, M.D., on June 12, 2025.