Sensitivity was 10 μV/division, low-frequency filter was 20 Hz, high-frequency filter was 2 kHz, sweep speed was 2 ms/division, duration of pulse was 0.2 ms, rate of pulse was 1/s, and the machine used was a Viking IV electromyograph.

This study was performed in the supine position.

Following the orthodromic method [1], the median sensory nerve conduction study was performed recording the sensory nerve action potentials (SNAPs) of the palmar cutaneous branch (PCB) at the distal forearm (Fig. 1). A pair of recording surface electrodes (R) was placed at the forearm in the bipolar derivation, along the median nerve course, with the orientation of the two recording electrodes along the line of the nerve. The active electrode (A) was placed at a 10 cm distance from the stimulating cathode (S), proximal to the distal crease at the wrist. The reference (R) electrode was placed proximally. The ground (G) strap electrode was placed around the wrist crease.

The sensory nerve conduction studies were done orthodromically. The rectangular pulses of 0.2 ms at 1 Hz were regularly delivered via a bipolar surface electrode in the palmar cutaneous branch (PCB) at the lateral thenar eminence, with the active cathode (−) proximal to the wrist crease and the anode electrode (+) placed distally. Stimulus intensity was gradually increased in milliampere (mA) to avoid the spreading to other nerve branches by means of volume conduction [2].

Peak latency (ms) was measured from the onset of the stimulus to the peak of the negative deflection of the SNAP. Negative peak amplitude (μV) was determined from the preceding positive deflection to the negative peak of the SNAP. Skin and room temperature were not given. Normal values (Table 1) were obtained from 25 normal subjects (age range 26–60 years, mean age 44.5 ± 12.0 years). The authors performed the nerve conduction technique on 8 patients (Table 2) with abnormal sensations in the thenar eminence as well as abnormal sensory distribution along the main branch (6 women and 2 men, 7 right hands and 1 left hand, age range 29–57 years, mean age 49.6 years).