Contact Heat Evoked Potentials Are Responsive to Peripheral Sensitization: Requisite Stimulation Parameters

Frontiers in Human Neuroscience, 2020 · DOI: 10.3389/fnhum.2019.00459 · Published: January 10, 2020

Simple Explanation

This study explores how to best measure the increased sensitivity to pain (peripheral sensitization) caused by capsaicin using a method called contact heat evoked potentials (CHEPs). The researchers tested different starting temperatures for the heat stimulation and found that starting at lower temperatures (35 and 38.5 degrees Celsius) allowed them to detect the effects of capsaicin, while a higher starting temperature (42 degrees Celsius) did not. This suggests that the nerve fibers responsible for the first pain sensation are activated earlier when the skin is sensitized by capsaicin, but only if the heat stimulation starts at a low enough temperature.

Study Duration

Not specified

Participants

13 healthy subjects (12 in final analysis)

Evidence Level

Not specified

Key Findings

1
Capsaicin sensitization resulted in increased pain ratings in the primary area of hyperalgesia.
2
Capsaicin sensitization resulted in reduced N2 latency, but only when stimulation was performed from 35 and 38.5◦C baseline temperatures.
3
Increasing the baseline temperature to 42◦C attenuated latency reductions, to the point that N2 latency was not signiﬁcantly diﬀerent following sensitization.

Research Summary

The study investigated contact heat stimulation parameters to detect peripheral sensitization related to topical capsaicin application, aiming to improve CHEP-based measurement of sensitization. Results showed increased pain ratings and reduced N2 latency after capsaicin application, but N2 latency changes were significant only with 35 and 38.5◦C baseline temperatures. The findings suggest that earlier recruitment of capsaicin-sensitized afferents occurs between 35 and 42◦C, implying conventional CHEP stimulation is suited to detect peripheral sensitization objectively.

Practical Implications

Improved CHEP Methods

Conventional CHEP stimulation with baseline temperatures below 42°C is effective for objectively detecting peripheral sensitization.

Understanding Pain Mechanisms

The study provides insights into the temperature-dependent effects of capsaicin on pain ratings and N2 latencies, suggesting separate mechanisms of peripheral sensitization.

Clinical Relevance

Capsaicin-sensitized N2 latencies acquired via 35°C baseline occurred earlier than previously reported normal values, suggesting clinical relevance in assessing peripheral sensitization.

Study Limitations

1
Capsaicin exposure always followed a recording session without capsaicin, which may have influenced the findings.
2
Randomization of recording sessions would not overcome the inability to successfully blind participants to the perceptual eﬀects of capsaicin
3
A relatively low number of subjects (n = 12) may have contributed to type II error in relation to some of our observations

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