The Impact of Efficacious Treatments for Major Depressive Disorder on Remission Rates of Specific Symptoms: A Re-Analysis of the Treatment of Depression Collaborative Research Program
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Major Depressive Disorder (MDD) is a highly prevalent mental disorder that will affect 12.2% of Canadians over the course of their lifetimes, and 4.8% annually (Patten, et al., 2006). One of the most robust findings in the MDD literature is that the gold-standard treatments – Cognitive-Behavioral Therapy (CBT), Interpersonal Psychotherapy (IPT), and anti-depressant medications - are equal in their efficacy, and superior to placebo. However, it is unclear whether rates of remission for certain types of symptoms differ among treatments with theoretically different mechanisms. This study re-analyzed data from the Treatment of Depression Collaborative Research Program, which included 158 adults with MDD randomized to CBT, IPT, imipramine or placebo. We statistically derived 4 factors from the baseline Hamilton Depression Rating Scale. We hypothesized that the rate of remission of somatic factors (sleep and appetite) would be most rapid in the group receiving imipramine plus clinical management (IMI-CM), and that the rate of remission for cognitive-affective factors would be fastest in IPT and CBT. Hierarchical regression analyses predicted the sum of symptom scores corresponding to each factor using linear and quadratic time (measured in weeks). Treatment-by-time interactions were entered in a stepwise fashion. There were no significant interactions found in the appetite factor, suggesting that all therapies acted on these symptoms at similar rates. Consistent with hypotheses, IMI-CM produced more rapid remission in sleep symptoms compared to psychotherapy. Surprisingly, IMI-CM was also more rapid at relieving cognitive-affective symptoms. The results lend partial support to the idea that different treatments for MDD may target specific symptoms at different rates according to their underlying mechanisms of action. The findings present some exciting possibilities for elevating response rates through empirically-based “tailored treatments”.