How is MG diagnosed?
MG is hard to diagnose because weakness is a common symptom of many disorders. Your doctor will ask you about your symptoms, take a medical history, and perform a physical exam. If your doctor thinks you may have MG, she or he may run some tests: • Antibody blood tests. Blood tests can detect the presence of high levels of abnormal antibodies that prevent normal nerve-to-muscle transmission. Most people with MG have abnormally high levels of acetylcholine receptor antibodies. But some people with MG test negative for these antibodies. Recently, another type of antibody, called MuSK antibodies, has been found in some MG patients who test negative for acetylcholine receptor antibodies. For these patients, a blood test that detects MuSK antibodies can be a useful diagnostic tool. Just how MuSK antibodies alter or damage nerve-muscle transmission isn’t clear. But patients who test positive for MuSK antibodies often have symptoms involving face muscles, swallowing, speech, and breathing.
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.
