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In addition to a complete medical and neurological evaluation, a number of tests may be used to establish a diagnosis of MG.
A diagnosis can be confirmed in several ways, including the following:
- Acetylcholine Receptor Antibody -- A blood test for the abnormal antibodies can be performed to see if they are present. Acetylcholine Receptor Antibody testing - Approximately 85% of MG patients have this antibody and, when detected, is a guaranteed diagnosis.
- Anti-MuSK Antibody testing - a blood test for the remaining 15% of seronegative (SN) MG patients, those who have tested negative for the acetylcholine antibody, 40-70% test positive for the anti-MuSK antibody. The remaining patients have an unidentified antibody causing their MG.
- Tensilon® test, The edrophonium chloride (Tensilon®) test is performed by injecting this chemical into a vein. Improvement of strength immediately after the injection provides strong support for the diagnosis of MG.
- Electromyography -- (EMG) studies can provide support for the diagnosis of MG when characteristic patterns are present. Repetitive Nerve Stimulation to check for a post-synaptic defect, Single Fiber EMG, or a muscle biopsy to look for antibodies may also be used.
- Single Fiber EMG -- studies can provide support for the diagnosis of MG when characteristic patterns are present.
Sometimes all of these tests are negative or equivocal in someone whose story and examination still seem to point to a diagnosis of MG. The positive clinical findings should probably take precedence over negative confirmatory tests.
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