Unfortunately, a delay of one or two years in diagnosis is not unusual in cases of myasthenia gravis. Because weakness is a common symptom of many other disorders, the diagnosis is often missed in people who experience mild weakness or in those individuals whose weakness is restricted to only a few muscles.
The first steps in diagnosing myasthenia gravis include a review of the individual's medical history and physical and neurological examinations. The signs a physician must look for are impairment of eye movements or muscle weakness without any changes in the individual's ability to feel things. If the physician suspects myasthenia gravis, several tests are available to confirm the diagnosis.
A special blood test can detect the presence of immune molecules or acetylcholine receptor antibodies. Most patients with myasthenia gravis have abnormally elevated levels of these antibodies. However, antibodies may not be detected in patients with only ocular forms of the disease.
Another test is called the edrophonium test. This approach requires the intravenous administration of edrophonium chloride, or Tensilon (r), a drug that blocks the degradation of acetylcholine and temporarily increases the levels of acetylcholine at the neuromuscular junction. In people with myasthenia gravis involving the eye muscles, edrophonium chloride will briefly relieve weakness. Other methods of confirming the diagnosis include a version of nerve conduction study that tests for specific muscle fatigue by repetitive nerve stimulation. This test records weakening muscle responses when nerves are repetitively stimulated. Repetitive stimulation of a nerve during a nerve conduction study may demonstrate decrements of the muscle action potential due to impaired nerve-to-muscle transmission.
A different test called single-fiber electromyography (EMG), in which single muscle fibers are stimulated by electrical impulses, can also detect impaired nerve-to-muscle transmission. Computed tomography may be used to identify an abnormal thymus gland or the presence of a thymoma.
A special examination called pulmonary function testing, which measures breathing strength helps to predict whether respiration may fail and lead to a myasthenic crisis.
This answer is based on source information from the National Institute of Neurological Disorders and Stroke.
More Answers from Donna Hill Howes, RN