Ulnar Nerve Conduction Study of the First Dorsal Interosseous Muscle in Korean Subjects

OBJECTIVE: To derive normative values for ulnar nerve conduction study of the active recording electrode on the first dorsal interosseous muscle (FDI) and the reference electrode on the proximal phalanx of the thumb. METHOD: Ulnar nerve motor conduction study with FDI and abductor digiti minimi muscle (ADM) recording was performed in 214 hands of 107 healthy subjects. Ulnar NCS was performed with 2 different recording electrode montages (ADM-base of 5(th) finger; FDI-thumb) and differences in latency and amplitude were compared. Using this technique, the initial positivity of ulnar compound muscle action potential (CMAP) was not observed in any response with FDI recording. RESULTS: The maximal values for distal motor latency to the ADM and FDI muscle were 3.8 ms and 4.4 ms, respectively. The maximal difference of distal motor latency between the bilateral FDI recordings was 0.6 ms. The maximal ipsilateral latency difference between ADM and FDI was 1.4 ms. CONCLUSION: Placement of the reference electrode on the thumb results in a CMAP without an initial positivity and the normative values obtained may be useful in the diagnosis of ulnar neuropathy at the wrist.