Signs, Symptoms and Diagnosis of Myasthenia Gravis

The U.S. government’s Women.gov Web site offers the following information about how myasthenia gravis is diagnosed:

Symptoms
The muscles that control eye and eyelid movement, facial expression, and swallowing are most often affected. The onset of the disorder may be sudden. Symptoms often are not immediately recognized as MG.

In most cases, the first noticeable symptom is weakness of the eye muscles. In others, difficulty in swallowing and slurred speech may be the first signs. While rare, first signs of MG can also include difficulty with breathing. The degree of muscle weakness involved in MG varies greatly among persons with this disease. Symptoms, which vary in type and severity, may include:

• Drooping of one or both eyelids ( ptosis)

• Blurred or double vision ( diplopia) due to weakness of the muscles that control eye movements

• Unstable or waddling gait

• Weakness in arms, hands, fingers, legs, and neck

• Change in facial expression

• Difficulty in swallowing and shortness of breath

• Impaired speech ( dysarthria)

• Shortness of breath

Diagnosis
Unfortunately, a delay in diagnosis of one or two years is not unusual in cases of MG. Weakness is a common symptom of many other disorders. The diagnosis is often missed in people who have mild weakness or in those whose weakness is restricted to only a few muscles.

The first steps of diagnosing MG include a review of the person's medical history and physical and neurological exams. If the doctor suspects MG, several tests are available to confirm the diagnosis.

• Antibody blood test. A special blood test can detect the antibodies that prevent nerves from signaling to muscles. While most people with MG have abnormally high levels of these antibodies, some individuals (about 10 percent) can actually test negative for antibodies. And, antibodies may not be detected if only eye muscles are affected.

• Edrophonium test. When this drug is injected, the weak eye muscles of people with MG will briefly get stronger.

• Nerve conduction test/repetitive stimulation. This is a test of specific muscle fatigue by repetitive nerve stimulation.

• Single fiber electromyography (EMG). In this test, pairs of single muscle fibers are stimulated by electrical impulses. It can detect impaired nerve-to-muscle transmission.

• Computed tomography (CT) or magnetic resonance imaging (MRI). These tests can help identify an abnormal thymus gland or a thymus gland tumor.