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 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:
- Rheumatoid factor (RF)—this test may be used to detect or rule out rheumatoid arthritis.
- Cyclic citrullinated peptide antibody (CCP)—may also be used to rule out rheumatoid arthritis.
- Antinuclear antibody (ANA)—may be used to rule out other autoimmune disorders such as lupus.
- Thyroid panel and thyroid antibodies—used to rule out Graves disease, an autoimmune condition associated with hyperthyroidism.
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.