The machine used was a Dantec Counterpoint electromyograph. Sensitivity, low-frequency filter, high-frequency filter, sweep speed, duration of pulse, and rate of pulse were not specified.

This study was performed in the supine position.

Following the antidromic method [1], signals were recorded using surface saline-soaked Velcro ring electrodes placed distally to the digits from the proximal stimulation of the median nerve (S) at the wrist. Sensory nerve action potentials (SNAPs) were recorded from digit I (Fig. 1), digit II (Fig. 2), digit III (Fig. 3), and digit IV (Fig. 4). Active ring (A) electrode was placed over the metacarpal (MCP) of digit I, digit II, digit III, and digit IV; the reference ring (R) electrode was placed on the distal (R) interphalangeal joint of the same digits. Every wrist–digit recording was made separately. A 10 cm distance between the recording and stimulating electrodes was used for wrist–digit I test, and a 13 cm distance between the recording and stimulating electrodes was used for wrist–digit II, wrist–digit III, and wrist–digit IV tests. For each digit, the distance was measured from the stimulating cathode to the active electrode over the MCP joint. The distance to digit I was also measured on a straight line with the thumb in the neutral position, neither actively adducted nor abducted. In no case did the distances need to be adjusted for excessively large or small hands in the patients studied. Ground (G) electrode position was not mentioned in the text; the figures show the ground electrode positioned on the palm.

Stimulations were applied to the median nerve proximal at the wrist; all supramaximal responses were obtained averaging at least five to ten times. Wrist stimulation (S) was made at a fixed 10 cm distance from the active ring (A) recording electrode placed distally to digit I (thumb) and at a fixed 13 cm distance from an active ring (A) recording electrode placed distally to digit II (index finger), digit III (middle finger), and digit IV (ring finger). The authors did not specify if surface disk electrodes or a handheld bipolar stimulator was used for palm stimulation.

Onset latency (ms) was measured from the onset of the stimulus to the onset of the negative deflection of the SNAP; peak latency (ms) was measured from the onset of the stimulus to the negative peak of the wave. Negative peak amplitude (μV) was measured from the stimulus artifact to the peak of negative deflection of the SNAP. Temperature of the limb was maintained at 34 °C using a thermostat-controlled infrared heating lamp with the sensor placed in the palm of the hand. Normal values (Table 1) were obtained from 30 subjects composed by healthy volunteers and patients referred for lower extremity radiculopathy (21 women and 9 men, age range 21–70 years, mean age 36 years). Pathological values (Table 2) were recorded from 59 consecutive patients (44 women and 15 men, age range 22–91 years, mean age 50 years) with clinical diagnosis of carpal tunnel syndrome (CTS).