To help diagnose myasthenia gravis (MG)
Anti-MuSK (muscle-specific kinase) Antibodies
When you have symptoms that suggest MG, such as a drooping eyelid, double vision, difficulty chewing or swallowing, weak neck muscles, and difficulty walking and the result of your acetylcholine receptor (AChR) antibody test is negative
A blood sample drawn from a vein
None
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How is the test used?
An anti-MuSK antibody test is used to help diagnose myasthenia gravis (MG) in people with signs and symptoms associated with MG but who test negative for AChR antibodies. Testing is used to distinguish MG from other conditions that may cause similar symptoms, such as chronic muscle fatigue and weakness.
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When is it ordered?
An anti-MuSK antibody test may be ordered when you have signs and symptoms that suggest MG and the result from an AChR antibody test is negative.
Some signs and symptoms of MG include:
- Drooping eyelid
- Double vision
- Decreased control of eye movement
- Difficulty swallowing and/or chewing, leading to choking, drooling and gagging
- Slurred speech
- Weak neck muscles
- Trouble holding up your head
- Difficulty breathing
- Difficulty walking and an altered gait
- Specific muscle weakness but normal feelings/sensations
- Muscle weakness that worsens during physical activity and improves with rest
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What does the test result mean?
MuSK antibodies are not normally present in the blood. A negative anti-MuSK antibody test means it is less likely that you have MG. However, a negative result does not rule out MG. In about 6% to 10% of MG cases, neither AChR nor MuSK antibodies are present. These individuals are said to have double-seronegative MG. Results from other tests for autoantibodies, such as anti-LRP4 (LDL-receptor-related protein 4) antibody test and anti-striated muscle antibody test, may aid in establishing a diagnosis.
If you have a positive test result for anti-MuSK antibodies and symptoms of MG, then it is likely that you have autoimmune muscle-specific kinase myasthenia gravis.
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How long will it take for results?
This test requires specialized instruments and trained lab personnel and is not offered by every laboratory. Your blood sample will likely need to be sent to a reference laboratory for testing, so it may take a few days for results to be available.
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How serious is myasthenia gravis (MG)?
Most people who have MG can live a normal or near normal life with treatment and monitoring. One of the most serious complications is a respiratory myasthenic crisis that can occur when muscles that control breathing are weakened. This can be a medical emergency and often requires hospitalization. For additional details, see the article on Myasthenia Gravis.
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Does it matter which antibodies I have?
Yes, the type of autoantibody may guide the treatment for MG. People with anti-MuSK antibodies may respond differently to medications than people with AChR antibodies.
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Is there anything I can do to prevent getting MuSK binding antibodies?
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Can MG be inherited?
Autoimmune disorders are not caused by changes or variants in a specific gene, so they are not considered inherited conditions. They can run in families, however. Some people may inherit a genetic change that causes congenital myasthenic syndrome, which is an inherited condition with similar symptoms as MG but a different cause. For additional details, see the links in Related Content.
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Is there anything else I should know?
People who have MG are more likely to also have other autoimmune disorders, such as rheumatoid arthritis or lupus.