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Myasthenia Gravis

Blocking antibodies

12/01/2008

Question:

Is it useful to test a person for blocking antibodies when they have tested negative for binding and modulating antibodies?

Answer:

The four most common antibodies checked are binding AChR, blocking AChR, modulating AChR, and the MUSK antibody. Binding antibodies are most commonly checked and are found in generalized and ocular myasthenia. They are absent in roughly 50% of ocular myasthenics and 10-20% of generalized myasthenics.. Modulating antibodies are thought to reduce acetylcholine receptors on muscle cells. They are detected in up to 90% of myasthenics, even when the binding antibodies are negative. But caution must always be used in making a clinical diagnosis based on a test, as the modulating antibody can be falsely positive in people who have recently taken muscle relaxants. Blocking antibodies and MUSK antibodies can also be checked, and if my clinical suspicion is high enough, I will send these tests. But remember-- antibody titers support a diagnosis of myasthenia; they do not make it. 

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Response by:

Robert W Neel, IV, MD Robert W Neel, IV, MD
Assistant Professor of Neurology
College of Medicine
University of Cincinnati