Role of endogenous pain modulation in chronic pain mechanisms and treatment

Abstract

Development and application of psychophysical test paradigms to assess endogenous pain modulation in healthy controls and in patients yielded large body of data over the last 2 decades. These tests can assist in predicting pain acquisition, in characterizing pain syndromes and related dysfunctions of pain modulation, and in predicting response to treatment. This chapter reviews the development of thought on pain modulation in the clinical setup, focusing on conditioned pain modulation, and update on accumulated data regarding the mechanism, protocols of administration, and applications in the clinic.

The Cerebrospinal Fluid in Severe Pain Conditions : Clinical, Pharmacological and Proteomic Aspects

“…In a recent review not restricted to neuropathic pain, Yarnitsky favours the vulnerability hypothesis (which seems to have some empirical support) but also states that these findings do not rule out the possibility that CPM itself can change during, and possibly due to, the presence of chronic pain [272]. Indeed, this may not be an either-or issue.…”

“…Importantly, there is an important and ongoing "chicken and egg" discussion concerning CPM [272], and this discussion also applies to the findings of Paper III, namely: Is defective endogenous pain modulation a risk factor for the development of pathological pain (I call this the vulnerability hypothesis), or is it a consequence of the pathological pain state (the consequence hypothesis)? In other words: What is the temporal variation of CSF-BE during the course of the development of peripheral neuropathic pain?…”

“…This is both the strength of the method (it is anti-dualistic and looks at the psychophysical "whole") and its limitation (it may be difficult or perhaps even impossible to disentangle the importance of the different components). For instance, the possible influence of distraction, expectation, suggestion, and placebo on CPM results have been discussed [272]. Even so, it has been convincingly argued that psychophysical studies will remain an important tool in human neuroscience [200].…”

“…A key relay station for this system is the medullary subnucleus reticularis dorsalis (SRD), also known as the dorsal reticular nucleus (DRt). In order to study the efficacy of the DNIC system, conditioned pain modulation (CPM) experiments can be carried out [137,272].…”

Endocannabinoids and Related Lipids in Chronic Pain: Analytical and Clinical Aspects

“…In addition, alterations in the endogenous pain modula-tion could be referred to as alterations in the descending "top down" inhibitory pain modulation pathways such as the well-studied PAG-RVM system [10]. The endogenous pain inhibitory ability has been studied in humans by conditioned pain modulation (CPM) activation (similar to diffuse noxious inhibitory controls (DNIC) in rats) and relies on the analgesic effect of a conditioning stimulus on a painful test stimulus ('pain inhibits pain') [11]. Deficit CPM has been reported in several chronic pain conditions [12,13].…”