Sensitivity was 5–50 μV/division, low-frequency filter was 20 Hz, high-frequency filter was 2 kHz, and the machine used was Nicolet Viking II electromyograph. Sweep speed, duration of pulse, and rate of pulse were not specified.

This study was performed in the supine position.

Three sets of nerve conduction studies were performed on each hand examined [1]. The three studies were chosen based on reports in the literature indicating a high sensitivity for the diagnosis of carpal tunnel syndrome (CTS) and because the units of measurement (latency difference between two sensory nerves) could be directly compared and/or added: (1) median–ulnar (8 cm) midpalmar orthodromic (palmdiff) – following the orthodromic method (Fig. 1), the median and ulnar sensory nerve conduction studies were performed. Palm to wrist sensory conduction studies were done orthodromically at the wrist. The active electrode (A) was placed proximal to the distal crease at the wrist; the reference (R) was placed proximally. For the median latency measurements (R1), the authors placed a block electrode over the median nerve at the wrist, between the tendons of the flexor carpi radialis (FCR) and the palmaris longus (PL) muscles, ideally proximal to the distal wrist crease. For the ulnar nerve latency measurements (R2), electrodes were placed just lateral to the tendon of the flexor carpi ulnaris (FCU), ideally proximal to the distal wrist crease. The electrodes for the median and ulnar recordings at the wrist were placed at an identical distance from the stimulating sites for the median and ulnar nerves on the palm (fixed 8 cm distance between the stimulating cathode on the palm and the active recording electrode at the wrist). The ground (G) electrode position was not specified in the report; the figure shows the ground electrode placed on the palm. The median (R1) and ulnar (R2) nerve recordings were made separately; (2) median–ulnar ring finger (14 cm) antidromic (ringdiff) – following the antidromic method (Fig. 2), the median and ulnar sensory nerve conduction studies were performed. Signals were recorded using ring electrodes, 14 cm distally from the wrist to digit IV (R). The active electrode (A) was placed proximally, with ≥ 4 cm interelectrode spacing between the active (A) and reference (R) electrodes. The ground (G) electrode position was not specified; the figure shows the ground electrode positioned on the palm of the hand. The median (R1) and ulnar (R2) nerve recordings were made separately; (3) median–radial thumb (10 cm) antidromic (thumbdiff) – following the antidromic method (Fig. 3), the ring electrodes were placed over digit I (thumb) to record the median (R1) and radial (R2) sensory nerves action potentials (SNAPs). The active electrode (A) was placed proximally, 10 cm from the stimulation points for median (S1) and radial (S2) nerves at the wrist. The reference (R) was placed distally with maximal possible interelectrode spacing from the active (A) electrode. The ground (G) electrode position was not specified in the report; the figure shows the ground electrode placed on the palm. The median (R1) and radial (R2) nerve recordings were made separately.

(1) Median–ulnar (8 cm) midpalmar orthodromic (palmdiff) – palm to wrist sensory conduction studies were done orthodromically with the stimulator placed, cathode (−) proximally, in the midpalm over the digital nerves between the metacarpal bones (2nd and 3rd for the median nerve, 3rd and 4th for the ulnar nerve). A fixed 8 cm distance from the active (A) electrode placed at the wrist was used for stimulation. Nerves were stimulated supramaximally (the duration and rate of stimuli were not specified). (2) Median–ulnar ring finger (14 cm) antidromic (ringdiff) – stimulation was applied at the wrist (proximally to the distal wrist crease) 14 cm proximally to the recording electrode (A) on the median nerve (S1), between the tendons of the flexor carpi radialis (FCR) and the palmaris longus (PL) muscles, ideally proximal to the distal wrist crease; stimulation was applied also on the ulnar nerve (S2), just lateral to the tendon of the flexor carpi ulnaris (FCU) muscle. The median and ulnar nerve supramaximal stimulations were made separately. (3) Median–radial thumb (10 cm) antidromic (thumbdiff) – stimulation was applied at the wrist, 10 cm proximally to the recording electrode (A) on the median (S1) and radial (S2) nerves. On the median nerve (S1), the stimulation was applied proximally to the center of the distal wrist crease and between the tendons of the flexor carpi radialis (FCR) and the palmaris longus (PL) muscles. On the radial nerve (S2), the stimulator was placed on the dorsolateral surface of the wrist. The median and radial nerves were supramaximally stimulated separately.

(1) Median–ulnar (8 cm) midpalmar orthodromic (palmdiff) – the latency (ms) difference (palmdiff) was calculated as the median nerve peak latency minus the ulnar nerve peak latency. (2) Median–ulnar ring finger (14 cm) antidromic (ringdiff) – the latency (ms) difference (ringdiff) was calculated as the median nerve peak latency minus the ulnar nerve peak latency. (3) Median–radial thumb (10 cm) antidromic (thumbdiff) – the latency difference (thumbdiff) was calculated as the median nerve peak latency minus the radial nerve peak latency. For all measurements, the peak latency (ms) was measured from the onset of the stimulus to the negative peak of the wave. Temperature was not specifically measured in all subjects, although subjects were given time to equilibrate in a warm room before testing. The authors developed a summary variable based on simply adding all three latency differences, the combined sensory index (CSI):