Effect of high temperature on neuromuscular jitter in myasthenia gravis.

To examine if the effect of temperature on neuromuscular jitter differs in myasthenics and normals, we performed single fiber electromyography (SFEMG) in 10 myasthenics and 10 healthy controls after heating the upper extremity to 37 and 42 degrees C. In each case, 10-24 mean consecutive difference (jitter) values were obtained at both temperatures. All jitters were pooled appropriately and the groups were compared with each other. The mean jitter was 33.4 +/- 10.4 micros at 37 degrees C and 28.2 +/- 11.4 micros at 42 degrees C in controls, and 48.3 +/- 18.3 micros at 37 degrees C and 54.8 +/- 24.9 micros at 42 degrees C in patients. Seven out of 10 patients showed SFEMG abnormalities at 37 degrees C. The number of patients with SFEMG abnormalities rose to 9 after heating to 42 degrees C. Heating decreases neuromuscular jitter in controls and increases it in myasthenics. SFEMG performed at higher temperatures may increase the diagnostic sensitivity of the method in myasthenia gravis. The change of jitter with temperature in opposite directions in myasthenics and normals could be helpful to detect neuromuscular dysfunction.