Sensitivity was 10 μV/division, low-frequency filter was 10 Hz, high-frequency filter was 2 kHz, and sweep speed was 1 ms/division. Duration of pulse, rate of pulse, and the machine used were not specified.

This study was performed in the supine position.

Following the orthodromic method [1], the median and ulnar sensory nerve conduction studies were performed. For both the median and ulnar nerves, digit IV to the wrist sensory nerve conduction studies were done orthodromically at the wrist (Fig. 1). For both the median nerve (R1) and the ulnar nerve (R2), the active electrodes (A) were placed proximal to the distal crease at the wrist; the references (R) were placed proximally. For the median nerve (R1), electrodes were placed between the tendons of the flexor carpi radialis (FCR) and the palmaris longus (PL) muscles. For the ulnar nerve (R2), electrodes were placed just lateral to the tendon of the flexor carpi ulnaris (FCU) muscle. Recording electrodes (10 mm) mounted on a plastic bipolar bar, with an interelectrode distance of 30 mm, were placed longitudinally at identical distances over the median and ulnar nerves at the wrist (130 ± 11.2 mm). The ground (G) electrode was placed on the palm of the hand, between the stimulating and recording electrodes. The median (R1) and ulnar (R2) nerve recordings were made separately.

Because digit IV has median and ulnar innervation, finger to wrist sensory nerve conduction studies were done orthodromically with stimulation by ring electrodes at digit IV with the cathode electrode (−) on the proximal interphalangeal joint and the anode electrode (+) on the distal interphalangeal joint of the same digit.

Onset latency (ms) was calculated from the stimulus onset to the potential onset; peak latency was calculated to the peak of the negative deflection of the sensory nerve action potential (SNAP). Peak-to-peak amplitude (μV) was measured from the negative peak to the positive peak of the SNAP. SNAPs were measured at 10 μV/cm and from 10 Hz to 2 kHz bandwidth and averaged at least 16 times. Distances (digit IV–wrist segment) were reported in millimeters (mm). Skin and room temperatures were not controlled. The authors studied 33 asymptomatic (Table 1) volunteers (18 men and 15 women, age range 16–81 years), and 43 patients (Table 2) with symptoms and signs of carpal tunnel syndrome (CTS) were divided in two groups: Group 1, 26 hands, patients with sensory digit II onset latency >2.9 ms, 3.5 ms peak and Group 2, 16 hands, patients with sensory digit II onset latency <2.9 ms, onset or 3.5 ms peak.