Mechanisms, mechanisms, mechanisms: it really does all boil down to mechanisms

Results from randomized controlled trials (RCTs) suggest that cognitive behavioral therapy (CBT), mindfulness-based stress reduction (MBSR), and acceptance and commitment therapy (ACT) produce at least modest gains in primary outcomes for people with chronic pain, although fewer RCTs for MBSR and ACT have been published at present than for CBT. “Do these treatments work?” The answer is a provisional “yes.” Another vital question—“How do these treatments work?”—was largely neglected until recently. Most treatment mechanism research has proceeded on a “specificity assumption” that, for instance, CBT generates improvements in pain and function primarily via changes in maladaptive pain-related cognitions (eg, pain catastrophizing). Evidence shows that CBT-based treatments produce significant preto posttreatment changes in such cognitions, and these changes are correlated with preto postchanges in outcomes. Findings also show similar mechanism effects for changes in mindfulness during MBSR and changes in cognitive flexibility and pain reactivity during ACT. Furthermore, studies using cross-lagged analyses suggest that early treatment changes inmechanisms predict latetreatment changes in outcomes. Methods of these studies were limited, however, because they examined only one kind of mechanism during only one kind of treatment. They could not show whether other mechanisms not specific to the target treatment were also at work, whether observed mechanism effects were proxy effects for actual mechanisms, or whether specific mechanism effects were tied to a single treatment. Other studies extended this research and examined the role of single mechanisms but across different treatments. Smeets and colleagues conducted secondary analyses of an RCT comparing CBT, physical exercise, and CBT plus exercise. Results showed that preto posttreatment changes in pain catastrophizing did not differ significantly between treatments and changes in pain catastrophizing predicted preto postchanges in outcomes comparably across them. Similar results were found for pain catastrophizing in a trial of CBT vs pain education. Such results call into question whether pain catastrophizing change is amechanism specific to CBT, but also suggest that pain catastrophizing change is an important but pervasive mechanism elicited by different treatments, even those not using deliberate cognitive change techniques. These studies, however, examined only a single mechanism. Turner and colleagues conducted secondary analyses of a large RCT comparing MBSR, CBT, and usual care for people with chronic low back pain. They examined whether mindfulness and pain acceptance—hypothesized to be mechanisms specific to MBSR—would increase more in MBSR than in CBT and whether pain catastrophizing and pain self-efficacy—hypothesized to be mechanisms specific to CBT—would change more in CBT than in MBSR. Only 2 of 9 comparisons betweenMBSR and CBT of preto postmechanism changes were significant and in directions opposite of the hypotheses; namely, pain catastrophizing decreased more in MBSR than in CBT and one aspect of mindfulness increased more in CBT than in MBSR. Turner and colleagues did not report analyses of change scores, but other investigators have. Vowles and colleagues showed significant changes from preto posttreatment in measures of both acceptance and pain catastrophizing during a CBT-based program, changes that correlated similarly with preto postoutcome changes. Acceptance and pain catastrophizing change scores were also correlated significantly. These findings were replicated in studies of CBT-based multidisciplinary chronic pain programs. Together, findings do not support the conceptualization that different treatments produce outcomes primarily along distinct pathways specific to certain interventions but instead raise the possibility that different treatments achieve gains through shared underlying mechanisms. CBT, MBSR, and ACT theories describe different principles by which people with chronic pain can aggravate or improve their experience, but extant data suggest that their theoretical distinctions may contribute little to actual outcomes, whereas their commonalities contribute much. This phenomenon intersects with another phenomenon: different treatments produce largely similar outcomes. A case in point is findings from the parent study of Turner and colleagues, which revealed no meaningful differences on primary outcomes between MBSR and CBT. Indeed, the Cherkin and Turner studies illuminate the crossroads that the author believes the psychosocial chronic pain treatment field has reached: different treatments produce similar outcomes and may do so via similar mechanisms. However, we still do not know precisely what those shared mechanisms are or how they are most effectively stimulated. Thus, we may profit from shifting the bulk of research attention away from the 10% of the tip of the therapeutic iceberg (ie, developing new treatments based on new theories) and focus more on the 90% of the hidden iceberg that carries most of the mass (ie, shared mechanisms). Profit us how? By doing so, we may be able to improve the effectiveness of psychosocial pain Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.