TRANSDIAGNOSTIC VERSUS DIAGNOSIS‐SPECIFIC CBT FOR ANXIETY DISORDERS: A PRELIMINARY RANDOMIZED CONTROLLED NONINFERIORITY TRIAL

Transdiagnostic cognitive-behavioral treatments for anxiety disorders have been gaining increased attention and empirical study in recent years in response to amassing data suggesting more similarities among anxiety disorder diagnoses than differences [1,2,3]. Symptom overlap tends to be the norm rather than the exception, and several authors have suggested the existence of shared underlying pathology across the anxiety disorders [1, 4, 5]. Additionally, rates of co-occurring Axis I disorders are extremely high, with comorbidity among the anxiety and depressive disorders reaching approximately 55%[6]. Transdiagnostic treatments are designed to focus on the commonalities among the anxiety disorders, and recent studies have suggested that transdiagnostic CBT can be beneficial for clients with co-occurring anxiety and depressive disorders [7] and complex anxiety diagnoses such as anxiety disorder not otherwise specified [8]. Additional impetus to investigate transdiagnostic treatment protocols relates to practical issues that often arise in providing anxiety treatments in clinical settings. Transdiagnostic group CBT may be preferable in settings where it is not feasible to provide a variety of diagnostically homogeneous groups[9], such as sparsely populated regions where it would be difficult to populate diagnosis-specific groups in a timely manner, or settings with a high demand for services and limited resources for providing individual or diagnosis-specific group treatments. Furthermore, the dissemination of empirically supported treatments for anxiety may be eased with transdiagnostic CBT since therapists could receive training in a single CBT treatment for anxiety rather than multiple, disorder-specific treatments[10]. Transdiagnostic treatment models have generally shown evidence of efficacy, although the standards of comparison have been limited. Erickson[11], for example, reported the results of an uncontrolled trial of a transdiagnostic group CBT program for 70 individuals with an anxiety disorder diagnosis. His results suggested significant decreases in self-reported anxiety and depression among clients completing the 11-week treatment. Further, six-month follow-up data from 16 participants suggested maintenance of treatment gains. Norton[12] reported the results of an open trial of the transdiagnostic CBGT using mixed-effects regression modeling of session-by-session anxiety data from 52 participants with an anxiety disorder. Results indicated that participants tended to improve over treatment, with no differential outcome for any primary or comorbid diagnoses. Effect sizes (d = 1.68) were comparable to average treatment effects reported in meta-analyses of diagnosis-specific CBT for anxiety diagnoses (see[13,14]). Ellard and colleagues[15] reported data from 15 participants undergoing an open trial of individual transdiagnostic CBT for emotional disorders, reporting that 11 (73%) were treatment responders and 9 (60%) achieved high end-state functioning. Norton and Hope[16] published the first randomized controlled trial of a 12-week transdiagnostic group treatment and found that approximately 67% of those receiving treatment, as compared to none of the waitlist controls, showed a reduction in diagnostic severity to subclinical levels. In a secondary analysis of the treatment data, Norton et al.[17] also noted significant decreases in depressive symptoms and the diagnostic severity of depressive disorders among those receiving treatment. Erickson et al.[18] also randomized 152 patients to either an 11-week CBGT program or a delayed treatment control condition. The immediate treatment group improved more than the delayed treatment controls at post-treatment. When diagnostic categories were examined separately, however, only patients with primary panic disorder showed greater improvement than controls, possibly due to the reduced sample sizes of these subgroup analyses. In a randomized clinical trial of a similar transdiagnostic anxiety treatment, Schmidt et al.[19] found that post-treatment outcomes on measures of anxiety (d's ranged from 1.31 to 1.62), depression (d = .70), and clinician-rated severity (d = 1.18) were also superior among patients receiving transdiagnostic anxiety treatment compared to waitlist controls. Importantly, these gains were maintained at six-month follow-up. Finally, Craske et al.[20,21] found evidence that a transdiagnostic computer-assisted CBT delivered in primary care settings was superior to usual care[20], and outcomes were similar across diagnoses[21]. Further, their data[21] suggested high acceptability and participation among both patients and practitioners. Norton[22] described a randomized clinical trial examining the efficacy of a 12-week transdiagnostic group CBT program in comparison to a 12-week comprehensive relaxation training program. Results from 87 treatment initiators suggested significant and statistically equivalent/non-inferior outcomes across conditions, although relaxation was associated with a greater rate of dropout despite no differences in treatment credibility. No evidence was found for any differential effects of transdiagnostic CBT for any primary or comorbid diagnoses. McEvoy and Nathan[23] utilized a benchmarking strategy—comparing observed effect sizes to those obtained from methodologically-similar studies—to compare the efficacy of their transdiagnostic CBT intervention for anxiety and depression to similar published efficacy trials. Data from 143 participants attending at least three sessions (30 with anxiety disorders, 38 with depressive disorders, 75 with comorbid anxiety and depressive disorders) indicated treatment effect sizes, reliable change indices, and clinically significant change indices that were highly similar to those obtained in methodologically similar diagnosis-specific treatment studies for major depressive disorder or specific anxiety disorder diagnoses. Finally, Norton and Philipp[24] reported a meta-analysis on the efficacy of transdiagnostic anxiety treatments, and noted a strong average within-group effect (d = 1.29) across studies. Although these previous studies demonstrate the efficacy of transdiagnostic treatments in reducing anxiety symptoms, what is not established is the comparative efficacy of transdiagnostic anxiety treatments to well-established diagnosis-specific group CBT protocols for specific anxiety disorders. The primary aim of the current study was to investigate the efficacy of a transdiagnostic anxiety treatment by comparison to group CBT treatments that specifically target individual diagnoses of panic disorder, social anxiety disorder, and generalized anxiety disorder using a treatment non-inferiority methodology[25]. Non-inferiority methods differ from traditional null hypothesis significance testing in that the null hypothesis tested is of treatment inferiority and the alternative hypothesis, should the null be rejected at α = .05, is of treatment non-inferiority. It was hypothesized that all participants would show a significant reduction in anxiety over the course of treatment, and that outcomes in the transdiagnostic and diagnosis-specific conditions would be non-inferior.