Background: Major depressive disorder (MDD) is a heterogeneous condition and individual patients are likely to be differentially responsive to specific treatments. In an exploratory factor analysis of three rating scales, the Genome-based Therapeutic Drugs for Depression (GENDEP) trial identified three factors that were differentially associated with outcome to nortriptyline and escitalopram. However, this factor analysis has neither been replicated or applied to a psychotherapy treatment.
Methods: We replicated the GENDEP analytic method in the Emory Predictors of Remission to Individual and Combined Treatments (PReDICT) study. The 17-item Hamilton Depression Rating Scale, Montgomery Asberg Depression Rating Scale, and Beck Depression Inventory were administered to 306 MDD patients in the PReDICT study, which randomized previously untreated adults to 12 weeks of treatment with cognitive behavior therapy (CBT), escitalopram, or duloxetine. Utilizing Item Response Theory methodologies, factor scores were derived from the three scales and the efficacy of the three treatments was compared for the identified factor scores.
Results: Four factors were identified: "Despair," "Mood and Interest," "Sleep," and "Appetite." These factors closely aligned with the factors identified in GENDEP. Compared to CBT, escitalopram and duloxetine produced more rapid but ultimately similar improvement on the Despair and Mood and Interest factors; no significant differences between treatments emerged on the other factors.
Limitations: The scales contained differing numbers of items pertaining to specific depressive symptoms.
Conclusion: The heterogeneity of MDD can be parsed into a consistent factor structure, with the factors showing differential rapidity, but ultimately similar, improvement across treatments.
Keywords: Biomarker; Duloxetine; Escitalopram; Item response theory; Precision medicine; Psychotherapy; Rating scales.
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