Background: The burden caused by chronic pain is significant, affecting at least 10 percent of the world ' s population. While internet-based treatments based on cognitive behavioral therapy (CBT) have been shown to be promising in this area, attrition levels vary significantly. The purpose of this study was to investigate predictor variables for participants' adherence to an internet-based CBT treatment for individuals with chronic pain as well as to investigate associations between adherence and treatment outcome.

Methods: Data for this study was retrieved from a randomized controlled trial including 95 individuals with chronic pain who received internet-based CBT. Treatment adherence was studied through three outcome variables: treatment progress, treatment completion and exercise completion. The predictor variables were grouped into four clusters: background variables (age, gender, marital status, level of education, and typical computer usage); the second cluster included health status variables (sick leave, current psychiatric diagnosis, previous psychotherapy for pain, current pharmacological treatment, previous depression, current depression, and current depressive symptoms); the third cluster included pain-related variables (opioid medication, history of pain, and pain symptoms) and the fourth cluster included motivation variables (measured with treatment preference, treatment credibility, compliance to the treatment schedule and contact with the therapists).

Results: Findings showed that treatment progress was predicted by higher treatment credibility at baseline, whereas participants who were behind schedule in the second week of the program finished fewer treatment modules. When analyzing each cluster of predictor variables separately, current depressive symptoms also predicted fewer completed treatment modules. Among the pain-related variables, higher pain acceptance was the only predictor for completing more treatment modules. Treatment completion (which in this study was defined as having completed at least 75% of treatment modules) was predicted by higher treatment credibility and fewer depressive symptoms at baseline, and was thus similar to the results regarding treatment progress. Finally, all adherence variables predicted the treatment outcome pain interference.

Conclusions: Low treatment credibility, depressive symptoms and falling behind the treatment schedule early on were the most important predictor variables for low treatment adherence, while a number of demographical and pain-related variables were not related to adherence. The results from this study may help clinicians identify patients who are less likely to complete, and thus benefit from, their pain treatment. Trial registration ClinicalTrials.gov NTC03316846.

Comorbid psychological problems are commonly related to chronic pain but addressing heterogeneous comorbidities in traditional settings is often difficult. Delivering individually tailored treatment using the internet could be a viable alternative. The present study investigates whether a guided, individually tailored and internet-delivered cognitive behavioral therapy (ICBT) could improve mood and reduce disability in individuals suffering from chronic pain and comorbid psychological distress. Participants were recruited from a pain clinic and randomized to either ICBT or waiting list. The participants (n = 187) individually tailored treatments included 6-13 modules targeting different types of psychological distress. Modules were designed to be completed weekly, and feedback was provided by clinicians. Participants completed an average of 5.1 (49.7%) modules, with 22.9% completing all assigned modules. Intention-to-treat analyses showed significantly larger improvements in depression, disability, pain acceptance, catastrophizing, and quality of life in the ICBT-group compared to the control group. Between-group effect sizes were very small or small at post for the primary outcomes depression (d = 0.18) and pain interference (d = 0.22). Other effect sizes ranged from very small to small, with the largest effect being improvements in pain acceptance (d = 0.3). All significant changes were stable at 12-month follow up.