Background: Functional impairment is associated with major depressive disorder (MDD), and patients with MDD often present with somatic symptoms.
Objective: To examine the relationships between improved global functioning and core depressive symptoms as well as painful and nonpainful somatic symptoms in patients with MDD.
Method: This post hoc analysis of 2 identical trials compared the efficacy of duloxetine with that of paroxetine or placebo as treatment of MDD. In the trials, patients with DSM-IV-defined MDD received duloxetine 80 mg/day (N = 188), duloxetine 120 mg/day (N = 196), paroxetine 20 mg/day (N = 183), or placebo (N = 192) for 8 weeks. The Sheehan Disability Scale (SDS), Maier subscale of the 17-item Hamilton Rating Scale for Depression, 21-item Somatic Symptom Inventory, and Visual Analog Scale for overall pain were used to measure functional impairment, core symptoms of depression, and nonpainful and painful somatic symptoms, respectively. Baseline-to-endpoint mean changes in SDS total and subdomains were measured using analysis of variance with last-observation-carried-forward Pearson partial correlations, and path analysis was used to assess the significance of associations and relative contributions of improvement in global functional impairment, depression, and somatic symptoms. The trials were conducted from November 2000 to July 2002.
Results: The difference between antidepressant treatment and placebo in SDS total and subdomains was significant (p < .001). At baseline and in change from baseline to endpoint, associations between global functional impairment and core depressive and somatic symptoms were all significant (p < .05). Path analysis demonstrated improvement of functional impairment attributed to treatment effect as 37.0% (core depressive symptoms), 13.0% (nonpainful somatic symptoms), and 11.0% (painful somatic symptoms).
Conclusion: In patients with MDD, over a third of functional improvement associated with antidepressant therapy was mediated through improvement in core depressive symptoms. In addition, a significant proportion of functional improvement, although to a lesser degree, was associated with the treatment of both nonpainful and painful somatic symptoms.