Diagnostic value of F-wave inversion in patients with early carpal tunnel syndrome

► F-wave inversion has not been reported in early stage CTS. ► The contribution of F-wave inversion to the diagnosis of early stage CTS may be quite valuable. ► This method can be added to the routine nerve conduction studies. Routine electrophysiological studies usually give normal results in patients with early stage carpal tunnel syndrome (CTS). Diagnostic significance of the F-wave inversion (the median of F-wave minimal latencies (FWML) exceeds a normal ipsilateral ulnar FWML by 1 ms) has not been previously reported in early stage CTS. In this study, our primary aim was to investigate the diagnostic value of F-wave inversion in early stage CTS. Additionally, we aimed to demonstrate any possible relationship between F-wave inversion and symptom scores of the Boston questionnaire and functional capacity in early stage CTS. The study included 60 early stage CTS patients who presented with a median sensory nerve conduction velocity of ≥50 m/s. The symptom severity and functional status of the patients were assessed by using the Boston questionnaire. The control group consisted of 45 healthy volunteers. We compared early stage CTS patients and healthy control subjects in terms of the results obtained from median-ulnar FWML. Existence of F-wave inversion was found in 32 (53.3%) of the early stage CTS patients and in 3 (8.7%) of the healthy controls ( p = 0.001). It was also found to be positively correlated with the Boston questionnaire scores ( p = 0.001, r = 0.41) and functional capacity scores ( p = 0.001, r = 0.41). The sensitivity and specificity of F-wave inversion for the diagnosis of early stage CTS were calculated as 53.3% and 93.3%, respectively. The addition of F-wave inversion measurement to the set of the routine nerve conduction studies can increase the reliability of the electrophysiological studies in patients with early stage CTS.