Does Interpersonal Loss Preceding Panic Disorder Onset Moderate Response to Psychotherapy? An Exploratory Study

Background: Little research has addressed moderators of treatment outcome for anxiety disorders, and none has considered interpersonal loss as a predictor of outcome.

Purpose: To examine the effect of interpersonal loss events within the 6 weeks preceding panic disorder onset as a moderator of outcome in a randomized controlled trial of Panic-Focused Psychodynamic Therapy (PFPP) and Applied Relaxation Therapy (ART). Researchers hypothesized that such loss events would predict better outcome in PFPP but would not affect ART outcome.

Method: Forty-nine subjects with panic disorder were randomly assigned to a 12-week course of PFPP or ART. Independent raters blinded to treatment condition and study hypotheses rated subjects on the Panic Disorder Severity Scale (PDSS) and Sheehan Disability Scale. Exploratory analyses assessed between-group effect size for PFPP and ART following standard moderator analytic procedures. The trial was conducted between February 2000 and January 2005.

Results: Three quarters of subjects reported a narrowly defined interpersonal loss (LOSS) in the 6 weeks preceding panic disorder onset. These subjects had a mean (SD) duration of panic disorder of 8.2 (9.5) years. PFPP was more efficacious than ART, but LOSS did not moderate PFPP outcome. An unexpected finding was that LOSS moderated ART outcome: subjects without LOSS showed no response to ART (PDSS mean (SD) change score = 0.00 [2.90]), whereas LOSS had a pre-post mean (SD) change score of 4.29 (5.60). Neither examination of potential confounding variables nor sensitivity analyses of assumptions regarding attrition altered these findings.

Conclusion: Interpersonal loss events preceding onset of panic disorder were more common even than in prior studies. These losses moderated outcome in ART, a therapy that does not focus on such losses. Implications and the need for future research before incorporating these findings into clinical practice are discussed.

Trial Registration: clinicaltrials.gov Identifier: NCT00128388