Long term reliability of nociceptive withdrawal reflex thresholds

Area of Science:

• Neuroscience
• Pain Research
• Clinical Trials

Background:

• The nociceptive withdrawal reflex (NWR) is a crucial polysynaptic spinal reflex for protecting the body from noxious stimuli.
• Assessing the nociceptive withdrawal reflex threshold (NWR-T) is vital in clinical trials evaluating the human nociceptive system.
• Current NWR-T assessment methods involve stimulation of the sole of the foot or the sural pathway, with prior studies favoring sole stimulation.

Purpose of the Study:

• To compare the retest-reliability and subjective pain ratings of two NWR-T assessment methods.
• To determine the optimal stimulation site for reliable and comfortable NWR-T measurements.
• To evaluate the long-term stability of NWR-T measurements.

Main Methods:

• Two NWR-T assessment methods were compared: stimulation at the sole of the foot and stimulation over the sural pathway.
• Retest-reliability was assessed over 21 days using an up-down staircase method and Bland Altman agreement analysis.
• Subjective pain was evaluated using a numeric rating scale (NRS).
• Electromyography (EMG) analyzed muscle activity in the biceps femoris and tibialis anterior muscles.

Main Results:

• NWR-T assessment was successful for all participants.
• The tibialis anterior muscle exhibited larger EMG reflex amplitudes.
• NWR-T values demonstrated greater variability compared to NRS pain ratings.
• Both stimulation sites yielded stable NWR-T results over 21 days.

Conclusions:

• Stimulation of the sole of the foot demonstrated superior retest-reliability compared to the sural pathway.
• Participants reported lower pain levels when stimulated over the sole of the foot.
• NWR-T measurements are reliable over extended periods and serve as a stable indicator of pain conditions.
• Based on reliability, EMG recordings, and pain ratings, sole-of-the-foot stimulation is recommended for NWR-T assessment.