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Myasthenia Gravis

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The goals with testing are to diagnose myasthenia gravis (MG), distinguish it from other conditions with similar symptoms, and to guide treatment. Some tests may be performed to monitor a person's health status over time.

Laboratory tests
Laboratory testing may include the measurement of one or more autoantibodies:

  • Acetylcholine receptor (AChR) antibodies—found in up to 90% of those with generalized MG and about 50% of those with ocular MG; this is the primary blood test for MG. There are three types of AChR antibodies: binding (most frequently tested), blocking, and modulating.
  • Anti-MuSK (muscle-specific kinase) antibodies—found in about 50% to 70% of those who are negative for AChR antibodies and have generalized MG.
  • Anti-striated muscle antibodies—found in about 80% of those with MG who have an enlarged thymus gland and indicate a significantly increased likelihood of the person having a thymoma (generally benign tumor of the thymus).

Other testing that may sometimes be ordered:

Non-laboratory tests

One or more of these evaluations may be done to aid diagnosis, especially if laboratory testing was inconclusive:

  • Tensilon test (acetylcholinesterase test using edrophonium)—a person is given a drug intravenously to see if muscle strength improves for a few minutes (for more on this, see MedlinePlus Medical Encyclopedia: Tensilon test).
  • Repetitive nerve stimulation and/or single-fiber electromyography—to evaluate neuromuscular response in a specific area.
  • A chest CT (computed tomography)—to detect an enlarged thymus gland or thymoma.
  • A brain and eye orbit MRI (magnetic resonance imaging)—this is not routine but can help rule out other causes of eye-related symptoms.

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