(PS2-C55) Are Sudden Gains in Cognitive-behavioral Therapy for SAD Related to Outcomes One and Two Winters Later?

Sudden gains, defined as large improvements in symptoms in a single between-session interval, have been associated with better outcomes in cognitive-behavioral therapy (CBT) for depression at post-treatment and over extended follow-up (Tang & DeRubeis, 1999). In CBT for seasonal affective disorder (CBT-SAD), a previous study found that participants with sudden gains had lower depression severity at post-treatment compared to those without sudden gains (Rohan et al., 2021). Here, we examined whether sudden gain status was related to depression severity at follow-ups one and two winters later.

Participants included 88 currently depressed adults with Major Depression, Recurrent with Seasonal Pattern who were randomized to 6-weeks of CBT-SAD (two 1½-hr group sessions/week) in a clinical trial. The primary outcome was the Structured Interview Guide for the Hamilton Rating Scale for Depression–Seasonal Affective Disorder Version (SIGH-SAD), administered weekly during treatment and at follow-ups one and two winters later. Using weekly SIGH-SAD scores during treatment (Weeks 1-6), we operationalized sudden gains as: (a) a 6 point or greater drop in SIGH-SAD between weeks; (b) the drop was ≥25% from the prior week’s SIGH-SAD score; and (c) a significantly lower mean SIGH-SAD score for the 2-3 weeks following relative to the 2-3 weeks preceding the gain.

We conducted an ANCOVA (sudden gains vs no sudden gains) on SIGH-SAD scores at each winter follow-up timepoint, controlling for pre-treatment SIGH-SAD. There was not a significant difference in mean SIGH-SAD scores between those who experienced a sudden gain and those who did not at first, F(1,82) = 1.37, p = .246, or second, F(1,79) = 2.28, p = .135, winter of follow-up. In re-running the ANCOVA using Beck Depression Inventory-Second Edition (BDI-II) scores as the outcome at each follow-up, controlling for pre-treatment BDI-II, participants with vs. without sudden gains did not differ on BDI-II scores at either follow-up (first winter: F(1,82) = 1.55, p = .217; second winter: F(1,80) = 0.51, p = .477).

Consistent with the literature on sudden gains, CBT-SAD subjects with sudden gains experience better outcomes at treatment endpoint. However, sudden gains during CBT-SAD were not associated with lower depression severity following treatment. We previously reported that change towards more flexible seasonal beliefs (i.e., thoughts about the seasons, light availability, and weather) mediates depression improvement during CBT-SAD and depression severity following CBT-SAD (Rohan, Burt et al., 2020, in press). Within seasonal depression, perhaps impacting seasonal beliefs is more important than sudden gains for CBT’s long-term outcomes.