Despite the overarching influence of the traditional categorical diagnostic system for mental health problems, there is now a substantial body of evidence and paradigm shift occurring towards transdiagnostic approaches to classification, research, and treatment of mental health difficulties. This is in part due to the growing recognition that the traditional diagnostic system is no longer fit for purpose (Dalgleish et al., 2020), as well as the increasing body of supportive evidence for transdiagnostic approaches (Andersen, Toner, Bland, & McMillan, 2016; Newby, McKinnon, Kuyken, Gilbody, & Dalgleish, 2015; Pearl & Norton, 2017; Reinholt & Krogh, 2014).
Clinical guidelines that are based on a categorical diagnostic system have led to a self-perpetuating cycle of development and endorsement of single-disorder-focused treatment approaches (e.g., the United Kingdom’s National Institute for Health and Care Excellence (NICE; Pilling, Whittington, Taylor, & Kendrick, 2011)). While there is some recognition of comorbid conditions, the large majority of recommended intervention packages are diagnosis-based. We can do better, and a growing number of researchers are making significant contributions to the evidence base for transdiagnostic protocols. Reinholt et al.’s study (2021) makes one such addition with their RCT for transdiagnostic group therapy for anxiety and depression.
David Barlow recognised that most psychological treatment approaches began as “adiagnostic” or “transdiagnostic”, and then over time these have been partitioned and refined for specific diagnostic presentations (Barlow, Allen & Choate, 2004). Over the past 20 or so years, a number of transdiagnostic clinical interventions have evolved that “. . . apply the same underlying treatment principles across mental disorders, without tailoring the protocol to specific diagnoses” (McEvoy, Nathan, & Norton, 2009, p. 21).
Numerous studies and reviews have found that transdiagnostic psychological treatments are equivalent or superior compared to comparison or control interventions which include either a diagnosis-specific intervention control, treatment-as-usual, or a waitlist control (Andersen, Toner, Bland, & McMillan, 2016; Newby, McKinnon, Kuyken, Gilbody, & Dalgleish, 2015; Pearl & Norton, 2017; Reinholt & Krogh, 2014). These reviews note the value in this work, but also recognise the need for further evidence supporting the added value of transdiagnostic treatments compared to existing interventions.
As part of the call for high-quality, large-scale RCTs with robust comparison conditions, Reinholt et al. delivered the Unified Protocol for Transdiagnostic Treatment of Emotional Disorders (UP) in a group format, and compared it to diagnosis-specific cognitive behavioral therapy (dCBT) for anxiety and depression in outpatient mental health services. Reinholt et al. hypothesized that the UP would not perform worse than dCBT in group treatment of anxiety disorders and depression, measured by subjective well-being (primary outcome) and symptoms (secondary outcomes) at the end-of-treatment.
The study team conducted a non-inferiority, randomised controlled trial (RCT), and assigned 291 participants with major depressive disorder, social anxiety disorder, panic disorder, or agoraphobia to 14 weekly sessions in transdiagnostic UP or single-diagnosis dCBT groups. The primary outcome was scores on the World Health Organisation 5 Well-Being Index (WHO-5) at the end of the treatment. Secondary outcomes were work and social functioning and both self-reported and clinician-rated symptoms of depression/anxiety. They assessed outcomes at baseline, end-of-treatment, and at a 6-month follow-up. A modified per-protocol and intent-to-treat analysis was performed.
At end-of-treatment, mean wellbeing scores for participants in the transdiagnostic UP group (n = 148) were non-inferior to those of participants in single diagnosis dCBT (n = 143; mean difference -2.94; 95% CI -8.10 to 2.21). Results on the wellbeing measure were inconclusive at the 6-month follow-up, as the outcomes for the dCBT group were significantly better than outcomes for the UP on the WHO-5, but the 95% confidence interval included the non-inferiority limit of a 9-point difference between the groups so the authors could not confirm inferiority status. Results for work and social functioning and depression/anxiety symptoms were non-inferior at both end-of-treatment and the 6-month follow-up. Participant satisfaction and rates of attrition, response, remission, and deterioration were similar across conditions.
Reinholt et al.’s RCT demonstrated that group-delivered UP was not worse than dCBT on measures of wellbeing, work and social functioning, and depression/anxiety symptoms for major depressive disorder, social anxiety disorder, panic disorder, and agoraphobia at the end of treatment in outpatient mental health services. The results at the 6-month follow-up were inconclusive, so the long-term effects of UP on well-being need further investigation, however, the results for symptom measures and exploratory outcomes at the 6-month follow-up showed that they were no worse than dCBT. This study suggests that the UP should be considered a viable alternative to dCBT for common anxiety disorders and depression in outpatient mental health services, particularly in light of the finding that client satisfaction and participant engagement and response to treatment were similar across conditions.
Strengths and limitations
The authors should be congratulated for such a significant piece of clinical research, delivered across multiple mental health services and coordinating a large number of clinicians and participants. This study has a number of strengths which aid in making a substantial contribution to the literature on transdiagnostic approaches. First, the study team utilised a robust, large, pragmatic RCT design, which was adequately powered to detect differences between the groups on the primary outcome measure. Further, the application of the trial protocol across multiple mental health services allowed the investigators to test the external validity and applicability of the treatment protocols. They also implemented rigorous treatment monitoring and therapist competence/adherence procedures, ensuring a robust comparison of treatment protocols.
Another challenge for studies of transdiagnostic treatments is choosing appropriate outcome measures to assess treatment efficacy (Stanton, McDonnell, Hayden, & Watson, 2020). Reinholt et al. selected the WHO-5 Wellbeing index, which captures wellbeing and euthymia across a range of clinical presentations and is not specific to diagnosis. The authors were prudent in including the Work and Social Adjustment Scale and the Symptom Checklist/Hamilton scales to measure symptoms of depression and anxiety, as well as a large number of secondary and exploratory measures to capture diagnosis-specific outcomes. The authors also note that more of the intervention could focus on positive affect in order to effect change on overall wellbeing rather than a focus of reduction in symptoms (even though these may better capture some individual difficulties). One challenge for transdiagnostic approaches to mental health problems is influencing change in health systems that are still largely driven by categorical diagnostic systems and use outcome measures that reflect this (e.g., NHS Psychological Services).
The authors noted a number of other limitations, including high attrition (although normal for a public mental health service, this reduced the ability to draw conclusions about the follow-up and exploratory outcomes), strong allegiance of the UP therapists to the UP, and lack of measurement of treatment expectancy. Given that the outcomes for the UP group were not inferior to the outcomes for the dCBT group, it is possible that a number of common therapeutic factors and shared variance across the treatment conditions accounts for a significant proportion of the variance in psychological treatment effectiveness. For example, evidence-based cognitive-behavioural techniques, treatment expectancy, and therapeutic alliance may account for the non-inferiority/equivalence of many transdiagnostic and diagnosis-specific treatment protocols (Cuijpers, Reijnders, & Huibers, 2019).
Future studies should dismantle the components of transdiagnostic and diagnosis-specific interventions in order to determine effective treatment components and common processes to demonstrate the added value of particular treatment protocols on primary and comorbid psychological problems (Barlow et al., 2017; Hayes & Hofmann, 2018). Reinholt et al. note the effect of the treatment programmes on both primary and comorbid problems overall, but it would be helpful to see the specific effects. It could be expected that transdiagnostic treatment protocols would show non-inferiority for primary disorder but the superiority of transdiagnostic protocols for comorbid disorders, however, this was not found in the current Reinholt et al., study, emphasising the need for future research targeting this question, and in determining the most effective and efficient treatment targets for a wide range of individuals (including matching participants to the most appropriate group therapy programmes).
Implications for practice
- If the study results are replicated, transdiagnostic group treatments such as the UP should be considered a viable alternative to standard disorder-specific CBT for common mental health problems (e.g., anxiety and depression) in outpatient mental health services.
- The study authors noted that there would be additional work required to implement this treatment programme widely across mental health services, but the findings from this study are very hopeful, and they note the practical benefits of implementing transdiagnostic group treatments.
- Transdiagnostic treatment protocols, especially when demonstrated to be non-inferior or equivalent to disorder-specific protocols, carry a number of practical advantages. Transdiagnostic programmes are likely more cost-effective to disseminate and implement a smaller set of transdiagnostic approaches than a much larger set of diagnosis-specific interventions. At a service level, groups do not need to wait for a certain number of participants with a particular diagnosis to form a therapy group. The study authors highlight this advantage with their group treatment programme, alongside Peter Norton’s Transdiagnostic Group CBT for Anxiety (Norton, Hayes, & Hope, 2004). Measures of cost-effectiveness should be included in future studies and service evaluations.
- Even though flexibility is important, universal transdiagnostic protocols are more suitable for groups compared to modular transdiagnostic protocols that can be flexibly delivered according to individual concerns (e.g., The Modular Approach to Therapy for Anxiety, Depression, Trauma, or Conduct Problems (MATCH-ADTC) for children, Chorpita, Daleiden, & Weisz, 2005 and the Shaping Healthy Minds protocol, Black et al., 2018).
Conflicts of interest
Melissa Black has an overlap in research interests with the study authors (here), hosted the 2018 Conference on Transdiagnostic Approaches to Mental Health Challenges, and worked on a trial of a novel transdiagnostic psychological therapy (protocol can be found here and preprint here).
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