Abstract
Background
This study investigated 1) if a prolonged noxious stimulus (24‐hr topical capsaicin) in healthy adults would impair central pain inhibitory and facilitatory systems measured as a reduction in conditioned pain modulation (CPM) and enhancement of temporal summation of pain (TSP) and 2) if acute pain relief or exacerbation (cooling and heating the capsaicin patch) during the prolonged noxious stimulus would affect central pain modulation.
Methods
Twenty‐eight participants (26.2 ± 1.0 years;12 women) wore a transdermal 8% capsaicin‐patch on the forearm for 24 hr. Data were collected at baseline (Day0), 1‐hr, 3‐hr, Day1 (post‐capsaicin application), and Day3/4 (post‐capsaicin removal) that included capsaicin‐evoked pain intensity, heat pain thresholds (HPT), TSP (10 painful cuff‐pressure stimuli on leg), and CPM (cuff‐pressure pain threshold on the leg prior vs. during painful cuff‐pressure conditioning on contralateral leg). After 3‐hr, cold (12°C) and heat (42°C) stimuli were applied to the capsaicin‐patch to transiently increase and decrease pain intensity.
Results
Participants reported moderate pain scores at 1‐hr (2.5 ± 2.0), 3‐hr (3.7 ± 2.4), and Day1 (2.4 ± 1.8). CPM decreased 3‐hr post‐capsaicin (p = .001) compared to Day0 and remained diminished while the capsaicin pain score was reduced (0.4 ± 0.7, p < .001) and increased (6.6 ± 2.2, p < .001) by patch‐cooling and ‐heating. No significant differences occurred for CPM during patch‐cooling or ‐heating compared to initial 3HR, however CPM during patch‐heating was reduced compared with patch‐cooling (p = .01). TSP and HPT did not change.
Conclusions
This prolonged experimental pain model is useful to provide insight into subacute pain conditions and may provide insight into the transition from acute to chronic pain.
from Wiley: European Journal of Pain: Table of Contents https://ift.tt/2t7iE0Y
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