A factor analytic study in bipolar depression, and response to lamotrigine.

Objective: There have been no previous factor analytic studies of the Hamilton Depression Rating Scale (HDRS) in samples with bipolar I depression, and no investigations of the utility of any derived factors in determining treatment response in this condition. This study aimed to identify and compare factors of a 31-item version of the HDRS (HDRS-31) in large samples of patients with bipolar depression and Major Depressive Disorder (MDD), then examine the responsiveness of such factors to lamotrigine compared with placebo in the bipolar depressed sample.

Methods: This multivariate analytical study was performed on 2 large depressed samples (one bipolar and the other MDD) that had been recruited for separate, contemporaneous, double-blind placebo-controlled trials of lamotrigine. The 2 studies had similar designs and assessment tools, the major measures being the Montgomery-Asberg Depression Rating Scale (MADRS) and HDRS-31. To identify the constructs underlying the scale, exploratory factor analyses were conducted using HDRS-31 baseline scores. Treatment responsiveness in the bipolar depressed sample-as indicated by improvement in the total MADRS and HDRS-31, as well as HDRS factors-were examined using both a mixed-effects analysis and individual time-point t-tests.

Results: Seven factors of the HDRS-31 were identified: I-"depressive cognitions," II-"psychomotor retardation," III-"insomnia," IV-"hypersomnia," V-"appetite and weight change," VI-"anxiety," and VII-"anergia." A significant therapeutic effect of lamotrigine in bipolar depression was found for the "depressive cognitions" factor (from week 3) and "psychomotor retardation" (from week 4).

Conclusions: This study has identified 7 factors of the HDRS in a large sample of patients with bipolar depression. The results suggest that that the clinical benefits of lamotrigine in acute bipolar depression are primarily upon depressive cognitions and psychomotor slowing.