Background: Although diagnostically dissociable, anxiety is strongly co-morbid with depression. To examine further the clinical symptoms of anxiety in major depressive disorder (MDD), a non-parametric item response analysis on "blinded" data from four pharmaceutical company clinical trials was performed on the Hamilton Anxiety Rating Scale (HAMA) across levels of depressive severity.
Methods: The severity of depressive symptoms was assessed using the 17-item Hamilton Depression Rating Scale (HAMD). HAMA and HAMD measures were supplied for each patient on each of two post-screen visits (n=1,668 observations). Option characteristic curves were generated for all 14 HAMA items to determine the probability of scoring a particular option on the HAMA in relation to the total HAMD score. Additional analyses were conducted using Pearson's product-moment correlations.
Results: Results showed that anxiety-related symptomatology generally increased as a function of overall depressive severity, though there were clear differences between individual anxiety symptoms in their relationship with depressive severity. In particular, anxious mood, tension, insomnia, difficulties in concentration and memory, and depressed mood were found to discriminate over the full range of HAMD scores, increasing continuously with increases in depressive severity. By contrast, many somatic-related symptoms, including muscular, sensory, cardiovascular, respiratory, gastro-intestinal, and genito-urinary were manifested primarily at higher levels of depression and did not discriminate well at lower HAMD scores.
Conclusions: These results demonstrate anxiety as a core feature of depression, and the relationship between anxiety-related symptoms and depression should be considered in the assessment of depression and evaluation of treatment strategies and outcome.