The comorbidity of anxiety and depression in general medical patients: a longitudinal study

In a general medical clinic setting, 880 patients were screened for depression by using the Diagnostic Interview Schedule version of the DSM-III and the Zung Self-Rating Depression Scale (SDS), as well as the Zung Self-Rating Anxiety Scale (SAS). Based on a morbidity cutoff index of 50 on the SDS and a positive DIS for depression, 112 patients (13%) were found to have a depressive disorder. The SDS showed a 97% sensitivity, a 63% specificity, and an 82% correct classification of depressed and nondepressed control patients. Based on the SDS results and SAS results when anxiety was considered present at a moderate severity level, the comorbidity of anxiety and depression was 67%. Depressed patients were followed for 1 year during which time they were retested with the SDS and SAS at five time points (6 weeks and quarterly). Fifty-one patients who met the criterion of a decrease of greater than or equal to 12 points in the SDS index were assigned to the improved group, 23 who met the criterion of an increase of greater than or equal to 12 points were assigned to the worse group, and 36 patients were assigned to the no-change group. Depressed patients who improved showed a significant decrease in anxiety based on SAS change scores; depressed patients who worsened showed a significant increase in their anxiety index. The decrease in the anxiety index of patients in the no-change group was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)