Myasthenia gravis is a chronic muscular disorder of the voluntary muscles which become weak and rapidly fatigue. The most commonly affected muscles are on the face, eyes, arms and legs. People who suffer from myasthenia gravis also find that muscles involved in chewing, swallowing and talking are also affected. Basically, the disorder is caused by a breakdown in the communication system between the nerves and muscles often in the form of autoimmune disease. The second form, and less common, is a congenital form which is not autoimmune in nature, but a genetic flaw at the neuromuscular junction. In either case the end result is the same.
Diagnosis of myasthenia gravis often involves both a clinical history, physical examination and several complex tests. While taking a history from the individual, the doctor will attempt to elicit as much as possible about all symptoms. Interestingly, it is important to note the time of day and what circumstances are occurring as well as what circumstances bring on the symptoms or make them better. If individuals find that specific muscles are more effective than others the physician should also note this.
Specific symptoms that are more suggestive of myasthenia gravis include weak speech, the head dropping forward without the patient feeling sleepy, weakness of the shoulders or hips, double vision or drooping eyelids which come and go or difficulty with chewing and swallowing.
In the doctors office the physician will also do neurological exam focused on findings that may occur with myasthenia gravis. The doctor will also look for symptoms that may indicate another diagnosis and tests will focus on the eyes, speech, swallowing, neck and arms and legs.
There are clinical tests that the doctor may order. The first is the ice test and the second the Tensilon test. In the ice test the doctor will look for improvement in eye drooping after having placed an ice pack or a cold pack on the eye for approximately 1 minute. In the Tensilon test the doctor examines for improvements after giving a medication, Tensilon. This particular medication works when injected directly into the blood stream and has a very short time in which it is effective.
Tests which may be administered outside of the physician’s office include nerve conduction studies during which an electrical stimulus is applied to the skin and a machine is used to watch the activity of the nerve and the signal sent to the muscle supplied by that nerve. The size of the response and the time the nerve takes to get the response to the muscle is recorded and then evaluated by the physician.
Another option is the single fiber EMG which is the most sensitive test of neuromuscular transmission. This test is like the standard EMG but it is technically a more difficult test and requires up to an hour to complete. For this reason other tests are usually performed first and this one is used only if other testing is normal but myasthenia gravis is still suspected.
The physician can also use blood tests to help in the diagnosis. These are not routine tests and are not ordered as part of a routine panel, but they can be done on a standard blood sample. In these blood tests the technicians are looking for the detection of certain antibodies to acetylcholine receptors. In individuals who suffer for myasthenia gravis the antibodies bind to the receptor proteins and block the function or damage it. These antibodies are often called auto antibodies and are present in individuals who suffer from myasthenia gravis which is immune mediated.
Additional tests which the doctor may order include a chest x-ray or CT scan of the chest looking for an enlargement of the thymus glands or the presence of the tumor in the thymus. Pulmonary function tests may be used to determine if the respiratory muscles are affected so that appropriate treatment protocols may be initiated. An eye examination may be recommended from an ophthalmologist to rule out other causes the double vision and drooping eyelids.
There is no one definitive test for myasthenia gravis but rather it is a diagnosis made by a physician after examining all of the test results. Each test has certain advantages and disadvantages which the physician will evaluate before rendering a decision. For this reason it is very important to have open communication with your doctor and communicate all of your signs and symptoms which may be important in the diagnosis of this disease.
The Australian Myasthenic Association: Diagnosis
Neuromuscular: Myasthenia Gravis diagnostic Tests
Myasthenia Gravis Foundaiton of AMerica: Test and Diagnostic Methods