Myasthenia gravis laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Laboratory Findings

Laboratory findings consistent with the diagnosis of myasthenia gravis include:

Acetylcholine receptor antibodies:

One of the most important steps in confirming the diagnosis of myasthenia gravis is detecting AchR-Ab. About 85 percent of patients with generalized myasthenia gravis are seropositive for this Abs.(8-9) these antybodies are specific for myasthenia gravis but in rare cases we have false positive such as lambert-eaton, motor neuron disease, polymyositis(10-15-16) and even in the disease not related to myasthenia such as primary biliary cholangitis and systemic lupus erythematosus.(17-18) since the patient can become seronegative after immune modulating therapy, this test should be done before treatment. (12)

MuSK antibodies:

About 38 to 50 percent of patients with generalized disease, who are seronagative for AChR-Ab, have antibodies against muscle specific receptor tyrosine kinase (MuSK) (12-20 ta 26) these antibodies are not commonly seen in patients with well-established ocular myasthenia gravis. (28-29) This test can be useful in patients who have the typical presentation of myasthenia gravis but are negative for AChR-Ab.(21)

Anti-striated muscle antibodies:

These antibodies are present in about 80 percent of patients with thymoma and in 36 percent of myasthenia gravis patients overlay.(9) in patients with early onset myasthenia (20 to 50 years old) these antibodies are useful in detecting thymomas.(9,42)

Antibodies to titin:

Antibody to this protein which is an intracellular muscle protein is seen in about 95 percent of patients with myasthenia gravis and thymoma and in 50 percent of patients with myasthenia without thymoma.(45)