The Effects of Stimulation Frequency Changes on Central Conduction Time in Short Latency SEPs in Multiple Sclerosis Patients

Abstract

Background: Somatosensory evoked potentials (SEPs) are widely used in the electrophysiological diagnosis of multiple sclerosis since 1970s. also well known and it is often regarded as being pathological more often than the absolute latencies. Objective: In this study our aim was to find out the effects of the change of stimulus frequencies on absolute latencies and central conduction time in median SEPs of multiple sclerosis patients. Material and method: Twenty five multiple sclerosis patients and 15 healthy subjects were taken into the study and median SEPs of 80 extremities were studied. During median SEP recordings the stimulus frequencies were changed by 2/sec, 4/sec, 6/sec and 9/sec both in the patient and control groups. N9 peak, N11 peak, N13 peak, N20 peak and N11-13 complex onset latency, N20 onset latency, peak central conduction time and onset central conduction time have been determined both in the patient and the control groups. All the parameters of different stimulation frequencies were compared statistically with each other both in the patient and the control groups. The parameters of the patient and the control groups were also compared statistically with one and other. Results: The results showed that N20 peak latency, peak central conduction time, N20 onset latency and onset central conduction time values were statistically significantly higher in the patient group when compared with the control group. In the patient group, the values of peak central conduction time in 4/sec stimulation frequency were statistically significantly higher than the values in 2/sec stimulation frequency (p< 0.01). The same was true for the values in 6/sec stimulation frequency when compared with the values in 2/sec stimulation frequency (p< 0.05). There were no such statistically significant results for peak central conduction time values of the control group when different stimulation frequencies were applied (p> 0.05). In the patient group, the values of onset central conduction time in 4/sec stimulation frequency were statistically significantly higher than the values in 2/sec stimulation frequency (p< 0.05). The values in the control group did not show any statistical differences again (p> 0.05). Conclusions: The results obtained in this study showed us that the change of the stimulation frequencies in the patient group enhanced the pathology seen in both peak and central conduction times whereas the normal controls were immune to this effect. Changing the stimulation frequency during short latency SEP recordings has not been studied in multiple sclerosis patients before. We believe that studies on stimulus frequency changes in SEPs in multiple sclerosis, will be very useful both for the electrophysiological diagnosis of MS and the physiological dynamics of SEPs.