Offset analgesia is not affected by cold pressor induced analgesia

Background and aims: Offset analgesia (OA) is a pain modulating mechanism described as a disproportionately large decrease in pain intensity evoked by a minor decrease in stimulus intensity. Precise mechanisms of OA are still not elucidated and studies are needed to evaluate factors modulating OA. The aim of this study was to investigate OA before and during tonic cold pain (thought to induce descending inhibition), in a group of healthy volunteers. Methods: A randomized, crossover study was performed in 17 healthy participants (8 males and 9 females). The OA paradigm lasted 35 s and was induced by the traditional method using thermal stimulation applied to the forearm. A constant control heat stimulus (CTL) paradigm was used as control to assess adaptation. Pain intensity was assessed continuously. For induction of tonic cold pain, the participants immersed their hand into 2 degrees C water for 2 min. After 1 min and 25 s, the heat stimulation (OA or CTL paradigm) was repeated to assess the modulatory effect of the cold pressor test. Results: It was possible to induce OA both before and during the cold pressor test. Tonic cold pain modulated the peak pain reported during both the OA (p = 0.015) and CTL paradigms (p = 0 .001) reflecting endogenous pain modulation. However, the magnitude of OA was not modulated by tonic cold pain (p > 0.05). Conclusions: The offset analgesia magnitude was not modulated by simultaneously tonic cold pain, thought to reflect another endogenous pain modulation mechanism.