High-temperature repetitive nerve stimulation in myasthenia gravis

High temperature enhances the decrement on repetitive nerve stimulation (RNS) in patients with myasthenia gravis (MG). However, the limit of this phenomenon at high temperature is unknown. Three-hertz ulnar RNS was performed in 7 patients with MG at a skin temperature of 32 degrees C and then with the hand in a 44 degrees C water bath. At 32 degrees C, the mean decrement preactivation was 5% (range, 0-24%); after 1 min of exercise, the mean decrement reached a maximum of 11% (range, 1-34%) 2 min postactivation. At a hand temperature of 42 degrees C, the mean decrement preactivation was 17% (range, 0-65%); after exercise, the mean decrement reached a maximum of 29% (range, 5-74%) 1 min postactivation. In 3 subjects, RNS was normal at 32 degrees C, but a definite decrement developed with heating. These findings demonstrate that very high temperature can improve the sensitivity of ulnar RNS for postsynaptic neuromuscular transmission defects.