The correlation between muscle and nerve fiber conduction velocities in thenar muscle is lost in case of carpal tunnel syndrome

Abstract

Objective and methods: This study investigated the relationship between muscle fiber conduction velocity (MFCV) and motor nerve conduction velocity (MNCV) in thenar muscle of 20 normal subjects and of 20 patients suffering from a moderate carpal tunnel syndrome. Our goal was to confirm the positive correlation between MFCV and MNCV and to assess the influence of carpal tunnel syndrome on this relationship. MFCV was calculated in voluntarily contracted thenar muscle using a multi-channel surface recording and a spike-triggered averaging technique.

Results: MFCV values ranged between 2.6 and 7.2 m/s (mean±SEM: 4.5±0.3) in normal subjects and between 3.5 and 6.9 m/s (4.7±0.2) in patients. Subjects and patients did not differ regarding MFCV values, but a correlation between MFCV and MNCV was found in normal subjects (P=0.0005) and not in patients (P=0.54).

Conclusions: A correlation between muscle and nerve conduction velocities existed in healthy subjects but was lost in case of moderate carpal tunnel syndrome. MFCV appeared to be insensitive to focal nerve conduction slowing.