The moderating effects of comorbidity on treatment outcomes: Results from a randomized controlled trial of two panic-focused psychotherapies

Introduction: Individuals with Panic Disorder with or without Agoraphobia (PD/A) suffer from high rates of comorbidity. The present study aimed to address a knowledge gap about whether psychiatric comorbidity at baseline differentially influences, or moderates, outcomes in PD/A focused treatments.Methods: Data were drawn from a doubly-randomized preference trial of Panic Control Therapy (PCT) and Panic-Focused Psychodynamic Psychotherapy (PFPP) [Svensson et al. 2021. The effect of patient’s choice of cognitive behavioural or psychodynamic therapy on outcomes for panic disorder: A doubly randomised controlled preference trial. Psychotherapy &Psychosomatics, 90(2), 107–118]. A total of 221 participants were randomly allocated to choiceof treatment (n = 101), random assignment to treatment (n = 99), or waitlist (n = 21). Participants allocated to waitlist were re-randomized to either the choice of treatment (n = 8) or random assignment conditions (n = 9) after three months. In the main trial, PCT was superior to PFPP at post-treatment with no between-group differences at 24-month follow-up. The presen tstudy uses data only the participants randomized to treatment (n = 108). Specifically, mixed effect modelling was used to estimate the moderating effect of baseline psychiatric comorbidity on total scores on the clinician-rated Panic Disorder Severity Scale (PDSS; primary outcome) and a composite measure of patient-reported symptoms/problems and their functional impacts(Symptom Impact) measured at post-treatment and during a 24-month follow-up phase.Results: The number of comorbid psychiatric disorders (Axis I and II) did not predict or moderate either outcome during the treatment phase. During treatment, PCT participants with Axis I comorbidity (any) did not significantly differ from their PFPP counterparts for PD severity but did for symptom impact. During follow-up, PCT participants with Axis 1 comorbidity (any) had significantly poorer outcomes than their PFPP counterparts for PD severity but not for symptom impact. In respect of specific forms of comorbidity, PFPP Participants with PTSD had better outcomes during treatment and follow-up, while those with Major Depression had better outcomes during follow-up. The presence of personality disorders and medication during treatment or follow-up failed to predict or moderate outcomes.Discussion: PCT and PFPP are moderately effective treatments for PD/A. In the present study, psychiatric comorbidity overall had little effect on outcomes from both treatments with small and complex effects for specific forms of comorbidity. Overall, the present study adds to a growing body of literature that suggests that psychiatric comorbidity is an unreliable predictor of treatment outcome for adults with PD/A. Further studies involving larger samples and longer follow-up intervals are warranted before firm conclusions can be drawn about whether specific forms of comorbidity moderate outcomes in evidence-based treatments for PD/A, and thus whether treatments like PCT and PFPP require modification to improve outcomes based on comorbidity.