Fever and evoked potentials in multiple sclerosis.

The somatosensory evoked potentials (SEPs) and visual evoked potentials (VEPs) were studied in 19 patients with multiple sclerosis; 17 controls were studied during fever (38.0 degrees - 39.7 degrees C) and 2-3 days following return to normal temperature. The latencies of components N20 and P114 were measured and specified as abnormal when their value exceeded the standard deviation of the controls by 2.5 times. The corresponding criterion for the evaluation of the amplitude of components N20 and P114 was a reduction in amplitude of more than 50%. In the controls fever did not cause significant changes in evoked potentials. On the other hand, patients with multiple sclerosis showed abnormalities in evoked potentials during fever in a greater number of recordings (26 of SEPs and 33 of VEBs) than after return to normal temperature (19 and 27 respectively). In addition, the average latency of components N20 and P114 was clearly greater in the patients during fever (N20 = 29.5 +/- 5.2 ms and P114 = 143 +/- 18.1 ms) than after return to normal temperature (N20 = 6.6 +/- 3.5 ms and P114 = 134 +/- 16 ms). The amplitude of components N20 and P114 in patients during fever was clearly smaller than after return to normal temperature. These differences were statistically significant. Finally, in two patients, a decrease was found, during fever, in the conduction velocity of the peripheral somatosensory pathway from the median nerve to the wrist at Erb's point.