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The following is a summary of “Effect of limb position change on capsaicin-evoked pain: Evidence of interplays between the vascular and nociceptive systems?” published in the October 2024 issue of Pain by Courtin et al. 

Researchers conducted a retrospective study to examine the mechanism behind the increased capsaicin-evoked pain when the arm is raised to a vertical position after capsaicin application on the volar forearm.   

They examined 20 healthy volunteers who received a 2% capsaicin patch on 1 forearm and a vehicle patch on the other. The patches remained in place for 60 minutes. Participants’ perceptions of the patches were assessed repeatedly before, during, and after the application, with the arm positioned both horizontally at rest and raised vertically. Additionally, capsaicin-induced secondary hyperalgesia was evaluated by mechanical pinprick stimuli and half of the participants were seated upright, while the other half lay supine to determine whether limb position affected capsaicin-evoked pain due to gravity.  

The results showed that a few minutes after patch application, raising the arm treated with capsaicin (but not the vehicle-treated arm) resulted in an increase in pain experienced at the patch site. This effect of raising the arm did not vary between participants in the supine and seated groups, suggesting it was related to the arm’s position relative to the ground rather than the body. In contrast, the mechanical secondary hyperalgesia and the effect of arm raising were strongly decorrelated at the final assessment after patch removal, indicating distinct underlying mechanisms.  

Investigators concluded that capsaicin-evoked pain was impacted by the limb posture, leading to an interplay between vascular and nociceptive systems.

Source: onlinelibrary.wiley.com/doi/abs/10.1002/ejp.4742