The process of diagnosing myasthenia gravis begins following the onset of symptoms, which may occur gradually or occur suddenly. Doctors obtain a medical history, conduct a physical exam to check for signs of muscle weakness, and ask about a family history of the disorder.
Screening for myasthenia gravis can be done with several different tests.
Edrophonium test indicates the presence of the disorder by administering edrophonium, an anticholinesterase drug; affected people experience a significant but temporary relief of muscle weakness.
Blood analysis looks for the elevated levels of acetylcholine receptor antibodies that are found in more than 85 percent of patients. Blood analysis also reveals the anti-MuSK antibody that occurs in about a third of people who have myasthenia gravis without the presence of the acetylcholine receptor antibodies. In some cases of myasthenia gravis, neither antibody occurs.
Repetitive nerve stimulation uses small pulses of electricity to test for muscle fatigue and reveals the gradual decrease in muscle function.
Single-fiber electromyography or EMG, detects problems with nerve-to-muscle impulses by electrically stimulating individual muscle fibers. Muscles affected by myasthenia gravis respond poorly to the stimulation compared to normal muscles.
Imaging scans such as computed tomography (CT scan) and MRI (magnetic resonance imaging) can reveal tumors that may be the cause of symptoms.
Genetic testing may discover conditions associated with a family history of myasthenia gravis.
Pulmonary function testing evaluates the strength of muscles that support breathing and may indicate the potential of a myasthenia crisis.
Because muscle weakness associated with myasthenia gravis also occurs with other conditions, a diagnosis may be difficult, requiring the skill of a neurologist familiar with the condition.