How does temperature affect the results of repetitive nerve stimulation (RNS) in the evaluation of myasthenia gravis (MG)?

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

Several factors can affect RNS results. Lower temperatures increase the amplitude of the CMAPs. Patients with MG may report clinically significant improvement in cold temperatures, and they typically report worsening of ptosis in bright sunlight or on a warm day. Therefore, maintaining a constant and perhaps higher-than-ambient temperature during RNS testing is important to bring out abnormalities of NMJ function. The temperature of the skin overlying the tested muscle should be at least 34°C.

Administration of AChE inhibitors before testing may mask the abnormality and consequently should be avoided for at least 1 day beforehand (even longer for long-acting agents).


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