Aims: The current study explore the relationship between the trajectories of primary panic disorder symptoms and secondary depressive symptoms during guided internet-delivered cognitive behaviour therapy for panic disorder. Materials and methods: The patients (N=143) were recruited from an ongoing effectiveness study in secondary mental health outpatient services in Norway. Weekly self-reported primary panic disorder symptoms and secondary depressive symptoms were analysed. Results: primary panic disorder symptoms and secondary depressive symptoms improved significantly during the course of treatment, and at six months follow-up. Parallel process latent growth curve modelling showed that the trajectory of depressive symptoms and trajectory of panic disorder symptoms were significantly related. A supplementary analysis with cross-lagged panel modelling showed that (1) pre-treatment depressive symptoms predicted a positive effect of panic disorder symptoms early in treatment; (2) high early treatment panic disorder symptoms predicted low depressive symptoms at post-treatment. Conclusions: Guided ICBT for panic disorder is effective for both primary panic disorder symptoms and secondary depressive symptoms. Patients with high pre-treatment secondary depressive symptoms may constitute a vulnerable subgroup. A high level of panic disorder symptoms early in treatment seems beneficiary for depressive symptoms outcome. A time-dependent model may be necessary to describe the relationship between PAD symptoms and depressive symptoms during the course of treatment.
Keywords: Internet; cognitive behavioral therapy; comorbidity; depression; panic disorder/therapy.