Anodal block: can this occur during routine nerve conduction studies?

Area of Science:

• Neuroscience
• Electrophysiology

Background:

• Understanding nerve conduction is crucial for diagnosing neurological disorders.
• Electrical stimulation parameters, including electrode polarity, can influence nerve response characteristics.

Purpose of the Study:

• To investigate the impact of stimulus polarity and cathode-anode distance on median nerve electrophysiological responses.
• To determine if anodal block occurs under specific stimulation conditions.

Main Methods:

• Bipolar electrical stimulation of median nerves at the wrist in five healthy subjects.
• Recording of compound sensory nerve action potentials (CSNAPs) from the index finger and compound muscle action potentials (CMAPs) from thenar muscles.
• Varying cathode-anode distances (5-30 mm) and reversing stimulus polarity.

Main Results:

• No significant differences in CSNAP or CMAP amplitude, duration, or morphology were observed with reversed stimulus polarity.
• A consistent increase in onset latency was noted when the cathode was proximal to the anode, proportional to cathode-recording electrode distance.
• Anodal block was not observed in this experimental setup.

Conclusions:

• Stimulus polarity reversal primarily affects nerve response latency, not amplitude or waveform, in median nerve stimulation.
• Latency changes are distance-dependent and related to the cathode's position relative to the nerve and recording site.
• The findings suggest that anodal block is not a significant factor under these specific stimulation parameters.