F-wave records with submaximal stimulation: sustainability of the data and subject discomfort levels

Background: F-wave studies are valuable electrodiagnostic tests with considerable roles in early diagnosis of diabetic neuropathy, detection of axonal neuropathies and focal proximal nerve dysfunctions. The recording of F-waves, however, requires recurrent supramaximal stimulation which entails subjects’ discomfort during the procedure. The present study hence attempted to assess the validity of the F-wave data obtained after submaximal stimulation thereby lessening the subject discomfort levels.Methods: The study was conducted on 64 healthy subjects in the age-group of 18-40 years with normal neurological examinations. F responses from median, ulnar, tibial and peroneal nerves by both supramaximal and submaximal stimulation were recorded. Subjects rated discomfort level on a visual analogue scale. Mean values of F-wave minimum latency, mean latency, mean duration, persistence, chronodispersion, F/M amplitude ratio and subject’s discomfort level obtained by the two techniques were compared by paired t-test. P value <0.05 was considered as statistically significant.Results: Mean values of F-wave mean latency, minimum latency, chronodispersion and stimulus duration were not found to be statistically significantly different in the groups (p>0.05). Mean persistence, mean F/M amplitude ratio and mean subject discomfort levels varied statistically significantly.Conclusions: F-wave data can be attained by submaximal stimulation. F-wave mean and minimum latency, chronodispersion and duration remain relatively stable, but more stimuli may be needed for accurate values. For F/M amplitude ratio and F-wave persistence, submaximal reference range would be required. Nonetheless, diminution in subject discomfort with valid F-wave latency values, favours low intensity stimulation