In these studies, we have had to infer that CBT reduces central sensitization: because CBT is effective at reducing chronic pain based on verbal self-report, and because central sensitization is a leading cause of chronic pain, we have inferred that CBT must reduce central sensitization. Now, we have a study that directly demonstrates it.
In their well-designed study, Salomons, et al., are the first to experimentally induce a form of central sensitization in a group of previously pain-free subjects, deliver a CBT intervention, and measure the reduction in central sensitization that results from the CBT intervention. As such, they are the first to demonstrate that CBT reduces central sensitization as measured in the laboratory and not simply rely on inferences based on self-reported pain levels.
The study design
The study consisted of 34 healthy women who did not have pain. Through a series of pain-provoking procedures, the researchers induced secondary hyperalgesia in these healthy women. Secondary hyperalgesia is a type of central sensitization. Central sensitization is largely considered a common, if not the most common, cause of chronic pain. In secondary hyperalgesia, the nerves in the general location of the pain become reactive in an increasingly wider area. As a consequence, it takes less and less stimuli to cause pain in this widening area around the site of the original pain.
Along side this series of pain-provoking procedures, the researchers provided half the group of healthy women with a few basic cognitive behavioral interventions for pain. The CBT intervention consisted of both providing the subjects with information about the sensory, cognitive, and affective aspects of pain and engaging them in cognitive restructuring in order to reduce the stress response that accompanies pain. Cognitive restructuring is an intervention that helps people to make sense of their pain differently, from understanding it as something that is alarming or frightening to understanding the pain as something that is more benign and not harmful or perhaps even beneficial. For the other half of women, they provided a psychotherapy focusing on becoming more assertive in interpersonal communication skills.
By comparing CBT for pain with a non-pain related psychotherapy, they attempted to determine the effectiveness of the CBT itself.
The provision of some form of psychotherapy to both groups is important because it controlled for the effectiveness of non-specific therapeutic factors of psychotherapy. Let me explain. To do so, we need to stray from our original topic a bit.
One of the most consistent findings in the last four decades of psychotherapy outcome research has been that a large percentage of what accounts for the effectiveness of psychotherapies are factors that are common to all psychotherapies. So, whether we are talking about cognitive behavioral therapy for pain or diabetes or depression, or psychodynamic therapy for dysfunctional relationship patterns, or family systems therapy for teenage behavior problems, they all tend to have some things in common, which contributes to what makes them effective. That is to say, despite having some obvious differences, they each share certain factors and these factors are in part what make them all effective.
These factors tend to be characteristics of the relationship between the provider and the patient. We tend to refer to these characteristics in general as the qualities of the ‘therapeutic relationship.’ For example, research consistently finds that, in whatever type of psychotherapy that one pursues, the development of a relationship with an expert provider who takes the time to listen to you and provide mutually respectful, caring, and honest feedback leads people to become motivated to make healthy behavior change – whether it is in learning how to manage pain or diabetes, overcome depression, develop healthy relationships, or change problematic teenage behaviors. In other words, the therapeutic relationship that you have with a healthcare provider is what leads, in part, to making healthy changes that can improve health.
So, in a study aiming to determine how CBT is effective for managing pain, Salomons, et al., needed to make sure that they were measuring what is unique to CBT for pain and not the general effectiveness that all the psychotherapies have in common. To do so, they compared CBT to a psychotherapy that was not for pain, but which would have the general therapeutic factors that are common to all therapies, including the CBT for pain. This study design thus allows the researchers to conclude that if CBT for pain is in fact more effective, then what’s making it more effective are those things that are unique to CBT. In other words, the therapeutic relationship might play a role in both psychotherapies equally, but if one is more effective, such as the CBT, then what’s pushing it over the top are those things that are unique to CBT.
So, let’s get back to what Salomons, et al., found.
Cognitive behavioral therapy and central sensitization
While both groups of study subjects reported less pain intensity, those who underwent CBT reported that the pain they had was less unpleasant and therefore more tolerable. These findings that CBT reduces pain and makes pain more tolerable are largely similar to most clinical trials of CBT for pain.
The more interesting and important finding was that the subjects who received CBT exhibited a 38% reduction in the area of secondary hyperalgesia. Recall that secondary hyperalgesia is a form of central sensitization in which the nerves around the site of pain become more reactive in a widening area. In this increasing area around the original site of pain, less and less stimuli are required to generate pain. Secondary hyperalgesia is thought to be one of the ways an acute injury can transition to chronic pain even after the acute injury has healed. In their study, Salomon, et al., experimentally induced secondary hyperalgesia and subsequently showed that CBT can reduce it.
To my knowledge, no previous study has directly demonstrated a reduction in a form of central sensitization with CBT interventions.
A possible explanation for this finding is that CBT reduces the stress response that occurs with pain. By coming to think about pain differently, the change in thinking corresponds to changes in the neural network of the brain. These changes in the brain might subsequently alter the hormonal and inflammatory responses of the stress response, which subsequently makes the nerves in the peripheral area around the site of the original pain less reactive. As such, the cognitive restructuring corresponds to changes in the brain that reduce the stress response, which lead to downstream reductions in nerve reactivity.
Whatever is the explanation, the findings of Salomons, et al., are important as they can lead us to greater confidence as to why CBT and CBT-based chronic pain rehabilitation programs are effective at reducing chronic pain.
Salomons, T. V., Moayedi, M., Erpelding, N., & Davis, K. D. (2014). A brief cognitive-behavioral intervention for pain reduces secondary hyperalgesia. Pain, 155, 1446-1452. doi: 10.1016/j.pain.2014.02.012
Author: Murray J. McAllister, Psy.D.
Date of last modification: 9-2-2014