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 up to 70% of those who are negative for AchR antibodies and have generalized MG.
- Anti-Striated muscle antibody test—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.
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 systemic lupus erythematosus.
- Thyroid panel—used to rule out Graves disease, an autoimmune condition associated with hyperthyroidism.
- 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.