Fast Five Quiz: Myasthenia Gravis Workup

Richard Nowak, MD, MS


July 08, 2021

Although false positive test results for anti-AChR antibodies are rare, they may be observed in thymoma without clinical MG, Lambert-Eaton myasthenic syndrome, graft-vs-host-disease, autoimmune liver disease, small cell lung cancer, rheumatoid arthritis treated with D-penicillamine, and motor neuron disease.

Approximately 2%-4% of patients with MG with a negative test result for AChR binding antibodies will have the modulating antibody, which is associated with an increased risk of thymoma. Up to 73% of patients with MG and thymoma have modulating antibodies. 

About half of the patients with negative test results for anti-AChR antibodies may have positive test results for antibodies to MuSK. These patients make up a distinct subgroup of MG, showing characteristics that are unique from patients with anti-AChR antibodies.

The antistriational antibody occurs in about 70%-80% of patients with thymoma and MG who are younger than 40 years. Data suggesting a positive test result for antistriational antibody in patients younger than 40 years should prompt a thymoma examination.

Learn more about the workup of MG.


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