Identification of optimal site of G1 placement for median orthodromic palmar nerve conduction study.

Abstract

G1 electrode placement at the distal wrist crease during the median orthodromic palmar nerve conduction study (NCS) could result in a false negative study if compression is more proximal. In this study we aimed to determine the effect of median G1 electrode placement on distal latencies and amplitudes. Methods Median orthodromic palmar NCS was performed with the G1 electrode at the wrist crease and 2 cm proximal, stimulating 8 cm distal to G1. The difference in the distal latencies and amplitudes between the 2 recording sites was calculated. In 26 controls and 25 carpal tunnel syndrome (CTS) patients, the mean proximal-distal latency difference and percent amplitude decrease (distal vs. proximal) was -0.085 ms/53% (controls) and -0.072 ms/45% (CTS). Distal latency is not significantly affected by G1 placement in the median orthodromic palmar NCS, but the amplitudes are nearly twice as high when G1 is placed 2 cm proximal to the wrist crease.