How should residual symptoms be defined in depressed patients who have remitted?

Symptomatic remission has been defined as a complete or near-complete absence of symptoms. Just as the distinction between remitters and nonremitters among treatment responders has clinical significance, the distinction between a complete and near-complete absence of symptoms itself might be important. Recent studies have reported a high frequency of residual symptoms in patients who are presumably in remission, and this raises questions about how residual symptoms are defined. In the present report from the Rhode Island Methods to Improve Diagnostic Assessment and Services project, we compared the prevalence of residual symptoms based on different cutoff scores on 2 self-report measures of depression and then determined the association between residual symptoms and indices of psychosocial morbidity. We administered the 17-item Hamilton Rating Scale for Depression to 274 psychiatric outpatients diagnosed as having DSM-IV major depressive disorder who were in ongoing treatment. The patients completed the Clinically Useful Depression Outcome Scale (CUDOS) and Quick Inventory of Depressive Symptomatology (QIDS) and measures of psychosocial functioning and quality of life. We examined the frequency of residual symptoms in the 142 patients scoring in the remission range on the Hamilton Rating Scale for Depression. For both the CUDOS and QIDS, the threshold to define symptom presence strongly impacted on the prevalence of residual symptoms. The association between residual symptoms, psychosocial functioning, and quality of life varied according to the threshold used to define the symptoms. On the QIDS, a cutoff of 1 was a more valid indicator of the presence of residual symptoms than a cutoff of 2, whereas on the CUDOS, we recommend a cutoff of 2 be used to indicate the presence of residual symptoms. Examination of the frequency of specific symptoms suggests that the choice of scale might impact on which residual symptoms are considered the most frequent in treatment remitters.