The role of itch and pain modulation in the prediction of phototherapy outcomes: a prospective cohort study

Objectives: Ability to predict which chronic itch patients will benefit from particular treatments is a challenge. Common features in itch and pain in respect to sensory elicitation, and mechanisms of processing including sensitization and inhibition at the peripheral and central levels, may serve to understand variability in treatment outcomes. As such this study aimed to explore whether phototherapy outcomes can be predicted by psychophysical parameters of pain and itch modulatory processing. Methods: Prospective cohort study on chronic-itch patients (n = 44) assessed before 20 treatments of NB UVB. Level of itch and pain reduction following painful stimulation (reflecting the ‘pain inhibits pain’ phenomenon) used to assess the top-down modulation response efficacy. Magnitude of Conditioned Pain Modulation (CPM) for itch (CPM-itch) and for pain (CPM-pain) (reflecting inhibition) and magnitude of temporal summation (TS) of pain (reflecting ascending facilitation pathways) assessed to predict treatment effect. Results: Higher improvement of itch symptoms following phototherapy was correlated with more efficient CPM-itch (r = 0.62, p <.001), but not magnitude of CPM-pain or level of temporal summation. Discussion: Findings emphasize the role of descending inhibition pathways in determining phototherapy efficacy in chronic itch patients. Such an evaluation-based approach may contribute to better patient selection for phototherapy improving patients’ disease outcomes.