Abstract
In carpal tunnel syndrome, depending on the severity and duration of compression, varied degrees of demyelination or axonal degeneration leads to low action potential amplitude with wrist stimulation. Amplitude drop across the lesion can distinguish demyelination from axonal degeneration. In 61 control and 127 consecutive CTS patient hands we recorded antidromic sensory nerve action potentials after palm and wrist stimulation to compare amplitude ratios. The latency, amplitude and velocity of median SNAPs were significantly different between normal and CTS groups (p<0.001). Although patients with milder involvement had similar distal latency to controls (p=0.977), SNAP amplitude and conduction velocity, being still in the normal ranges, were significantly different from controls (p<0.001). SNAP wrist to palm amplitude ratio was 0.81 ± 0.12 in controls. In 87 hands mean amplitude ratio was significantly lower than it was in normal group (0.53 ± 0.23, p<0.001) but the remaining forty hands with milder involvement had a mean amplitude ratio (0.75 ± 0.23) similar to controls (p=0.127). There was a significant reduction of SNAP amplitudes at the wrist compared to the palm in 54 % of hands. Comparison of amplitudes between wrist and palm segment may give information about conduction block.