Enhanced Itch Intensity Is Associated With Less Efficient Descending Inhibition Processing For Itch But Not Pain Attenuation In Chronic Dermatology Patients

Objectives. The study aims were 1) to investigate the direction of mutual inhibitory pathways on itch intensity by utilizing conditioned pain modulation paradigms for pain and itch attenuation and 2) to explore whether itch severity is affected by the individual pain sensitivity profile, as well as pain scores reported during the tests and the past week. Design. Cross-sectional. Setting. Testing was conducted at the Department of Dermatology, Rambam Health Care Campus. Subjects. Forty patients suffering from chronic skin disorders associated with itch and treated in the Dermatology Clinic at Rambam Health Care Campus participated in the study. Methods. Efficacy of descending inhibition was evaluated by two conditioned pain modulation (CPM) paradigms: by pruriception (CPMItch) induced by cold and heat as counterstimuli to inhibit itch intensity and by nociception (CPMPain) Severity and interference of clinical pain were assessed using the Brief Pain Inventory (BPI). Results. Robust CPMItch responses were obtained following the various noxious stimulations. No associations were observed between CPMPain and CPMItct, itch severity, skin disease severity, and clinical pain symptoms. According to the linear regression model, itch severity was independently associated with less efficient CPMItch (B = -0.750, P< 0.001) and more efficient CPMPain (B=0.031, P= 0.016), which affects itch in opposing manners. Conclusions. Findings indicate that the intrinsic capacity to inhibit pain and itch by exposure to exogenous noxious stimuli autonomously affects itch intensity in an opposing manner. These findings may shed new light on the mutual mechanistic similarity and dissimilarity between pain and itch and their hierarchy.