Effect of anodal stimulation in f-wave examinations

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Effect of anodal stimulation in F-wave examinations
Takamichi Kanbayashi1, Takaharu Yamauchi2, Chizuko Oishi1,3, Yosuke Miyaji1, Masahiro Sonoo1

1Department of Neurology, Teikyo University School of Medicine, Itabashi, Japan

2Clinical Laboratory Department, Ookuma Hospital, Nagoya, Japan

3Department of Neurology, Kyorin University, Mitaka, Japan
Background: It has long been believed that anodal block occurs at the anode during bipolar stimulation. However, 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. In this study, we investigated to assess how anodal stimulation affects F-wave examinations, and investigate the best way of preventing it.

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: Anodal stimulation can be pitfall in F-wave examinations. However, results from this study, we found anodal stimulation is difficult to occur if shifted the proximal anode a little from the nerve.

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