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). Conclusion 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.