Investigation of anodal stimulation and its implications for F-wave examinations.

INTRODUCTION: Recent studies have shown that stimulation occurs at the anode of stimulating electrodes instead of anodal block. This phenomenon may be a pitfall in F-wave examinations.

METHODS: Subjects included 10 healthy volunteers. Their ulnar nerve was stimulated at the wrist with the cathode placed distally. Antidromic impulses were evaluated using mixed nerve action potential (MNAP) at the elbow.

RESULTS: Anodal stimulation occurred for both sensory and motor fibers at 22 mm proximal to the anode, on average, which may theoretically shorten the F-wave latency by about 0.8 ms. Displacement of the anode away from the nerve made anodal stimulation less likely. In contrast, displacement of the cathode away from the nerve lowered the threshold for anodal stimulation, a newly found interaction between cathode and anode.

CONCLUSIONS: In this work we identified detailed features of anodal stimulation and potential influence on F-wave examinations. Muscle Nerve 56: 51-56, 2017.