Pain Modulation: From Conditioned Pain Modulation to Placebo and Nocebo Effects in Experimental and Clinical Pain

Abstract 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 CPMItch, 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.

Download Full-text

Understanding Central Mechanisms of Acupuncture Analgesia Using Dynamic Quantitative Sensory Testing: A Review

Evidence-based Complementary and Alternative Medicine ◽

10.1155/2013/187182 ◽

2013 ◽

Vol 2013 ◽

pp. 1-12 ◽

Cited By ~ 14

Author(s):

Jiang-Ti Kong ◽

Rosa N. Schnyer ◽

Kevin A. Johnson ◽

Sean Mackey

Keyword(s):

Pain Modulation ◽

Conditioned Pain Modulation ◽

Acupuncture Analgesia ◽

Mechanistic Studies ◽

Sensory Testing ◽

Descending Inhibition ◽

Future Directions ◽

Nociceptive Transmission ◽

Clinical Pain ◽

Neurophysiological Data

We discuss the emerging translational tools for the study of acupuncture analgesia with a focus on psychophysical methods. The gap between animal mechanistic studies and human clinical trials of acupuncture analgesia calls for effective translational tools that bridge neurophysiological data with meaningful clinical outcomes. Temporal summation (TS) and conditioned pain modulation (CPM) are two promising tools yet to be widely utilized. These psychophysical measures capture the state of the ascending facilitation and the descending inhibition of nociceptive transmission, respectively. We review the basic concepts and current methodologies underlying these measures in clinical pain research, and illustrate their application to research on acupuncture analgesia. Finally, we highlight the strengths and limitations of these research methods and make recommendations on future directions. The appropriate addition of TS and CPM to our current research armamentarium will facilitate our efforts to elucidate the central analgesic mechanisms of acupuncture in clinical populations.

Download Full-text