Pain Modulation Effectiveness: An Experimental Study Using Repeated Conditioned Pain Modulation as an Intervention and Analyzing Potential Predictors in Healthy Adults.

Background:

Pain is a widespread health condition that has a large burden on individuals, families, and society. Of the 39.4 million adults with pain that occurs most days and persists for more than three months, nearly two-thirds deem it "constantly present," and over half define it as "unbearable and excruciating". Pain may be classified as physiological and pathological. Nociceptive and inflammatory pain are physiological states that are protective and adaptive, whereas pathological pain is nonprotective and maladaptive.

The conditioned pain modulation (CPM) paradigm is a dynamic QST measure of a pain inhibitory process that lessens pain sensitivity in response to a remotely applied painful stimulus and is used to assess the ability of the person to endogenously inhibit pain. CPM may be a valuable tool in directing mechanistic-based approaches for treating painful conditions. For example, individuals with painful diabetic neuropathy and poorly functioning CPM have more significant analgesia when given duloxetine, a medication that augments conditioned pain modulation. Additionally, identifying and treating the source of pain is associated with positive changes in CPM. Healthy individuals demonstrate more efficient CPM when compared with people in pain and a systematic review of adults with chronic pain revealed that CPM efficiency improves after a reduction in pain. For example, total hip arthroplasty for treating painful osteoarthritis reduces pain and improves post-operative CPM. Collectively, these studies suggest that the CPM test has the potential to predict risk and treatment outcomes for chronic pain., therefore CPM may be considered an essential treatment moderator and mediator.

Activation of these central mechanisms (endogenous inhibitory systems) has also been proposed as the mechanism underpinning interventions used to treat various pain conditions. For example, evidence suggests that descending pain inhibitory systems (central mechanisms) play a fundamental role in mediating the analgesic effect of manipulation-induced pain modulation. Manual therapy activates afferent neuronal inputs that stimulate the central nervous system to inhibit pain through descending modulation. Like manual therapy, CPM inhibits pain through descending modulation. Continuous stimulation of central mechanisms through CPM should therefore alter pain processing and improve pain inhibition.

However, few studies have used CPM as an intervention, and none answer these research questions: 1) Does repeated exposure to conditioned pain modulation affect pain sensitivity? 2) Is analgesic efficacy of the nervous system predicted by the CPM effect? 3) Does CPM have therapeutic implications?