The relationship of median nerve F-wave parameters with severity and subtypes of carpal tunnel syndrome 1

Abstract

Purpose:

F-wave analysis may help affirm or disprove a compression neuropathy. In this study we have analysed the effects of focal median nerve injury on F wave in Carpal Tunnel Syndrome (CTS).

Method:

We studied 57 patients (100 hands) with clinical and electrophysiological CTS and 31 (62 hands) healthy subjects. Median nerve F-waves were evaluated following 10 supramaximal stimuli and recording from abductor pollicis brevis muscles. Minimum, maximum, and mean F-wave latencies, frequency of the F wave (Fp), chronodispersion ( $F_{CD}$ ), mean F/M amplitude ratios (mF/M-amp) and F-wave conduction velocity (FwCV) were evaluated.

Results:

The CTS patients showed prolonged F-wave latencies, decreased Fp, and an increase of the $F_{CD}$ as compared with normative values. Absent F wave was presented in 8 of 34 hands (23.5%) with severe CTS patients. In the severe group, the FwCV was significantly slower ( $p < 0.001$ ) and the mF/M-amp was significantly higher ( $p < 0.001$ ) than that of mild and moderate groups, respectively. Also, the mF/M-amp was significantly greater and Fp was lower in the axonal type than in the demyelinating type. The $F_{CD}$ was not different among groups. A strong positive correlations between mMDL with Fmin ( $r = 0.81$ , $p < 0.000$ ), Fmean ( $r = 0.80$ , $p < 0.000$ ) and Fmax ( $r = 0.71$ , $p < 0.000$ ) were revealed.

Conclusion:

Results support the differing effects of demyelinating and axonal injury on F-waves and suggest that the mF/M-amp ratio and FwCV, which is influenced by neuronal damages in the distal segment of the median nerve, is useful in the discrimination of CTS severity.

Keywords

Carpal Tunnel Syndrome median nerve F waves nerve conduction studies subtypes