Increased contact heat pain and shortened latencies of contact heat evoked potentials following capsaicin-induced heat hyperalgesia.

Objective: To examine changes in contact heat evoked potentials (CHEPs) and perceived pain intensity following acute sensitization with topical capsaicin.

Methods: CHEPs were recorded before and after 20 min of topical capsaicin application (200 μl, 5%) during skin warming in 22 healthy subjects. To evaluate the sequence effects and skin warming on CHEPs, 10 of these subjects also participated in a control study.

Results: Topical capsaicin yielded an increase in contact heat evoked pain ratings (p < 0.0001) and a shortening in N2 latency from a mean 345.2 ± 37.2 ms to 310.2 ± 38.5 ms recorded from the vertex position (p = 0.003, paired t-test). No difference was found in the N2-P2 peak-to-peak amplitude (p = 0.83). These results were unchanged after controlling for sequence effects and skin warming. Following capsaicin, ultralate CHEPs (N2a latencies 970-1352 ms) were recorded in three subjects.

Conclusions: Our study showed a decrease in late CHEPs latencies and appearance of ultralate potentials compatible with sensitization of Aδ fibers and C fibers. Conclusions: Contact heat may be a useful tool to assess sensitization of the pain system.