How does tetanic contraction affect repetitive nerve stimulation (RNS) for myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

During post-exercise facilitation, accumulation of calcium inside the terminal axon causes enhanced mobilization and release of ACh, which overcomes the reduced number of AChRs at the NMJ and thus leads to larger EPSPs with additional recruitment of muscle fibers, resulting in a larger CMAP. In MG, this potentiation may normalize RNS results.

In the post-exercise exhaustion phase, the NMJ is less excitable, and even fewer EPSPs reach threshold. Thus, some patients with an equivocal abnormality on RNS during the resting phase may show clear-cut abnormalities during the post-exercise exhaustion phase.


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