Residual Symptoms Were Differentially Associated with Brain Function in Remitted Patients with Major Depressive Disorders

Background: The desirable goals of the treatment of major depressive disorder (MDD) are considered both to achieve symptom remission and to help the patients be restored to their premorbid levels of functioning. Remission has often been defined clinically as a threshold using standardized scales. Such a definition, however, allows several residual symptoms to be present in the remitted state. The aim of this study was to examine the relationship between the levels of residual symptoms and social functioning and also the relationship between residual symptoms and brain function.

Methods: The subjects were 21 patients with MDD in remission, defined operationally using clinician-rated 17-item Hamilton Depression Scale. Depressive symptoms and social functioning were self-assessed with the Japanese versions of the Center for Epidemiologic Studies Depression Scale (CES-D) and the Social Adaptation Self-evaluation Scale (SASS), respectively. Brain function was measured by the changes in concentration of oxy-hemoglobin ([oxy-Hb]) in the prefrontal and temporal cortices during verbal fluency task using near-infrared spectroscopy (NIRS).

Results: The mean CES-D total score was 18.0, s = 13.2, indicating that they have on average mild depression. Scores of CES-D total and those of its four factors showed a significantly negative correlation with the SASS total score. Among the four factors, "Interpersonal problems" factor showed the strongest correlation with it. CES-D total score and those of its three factors, "Depressed affect", "Somatic and retarded activity" and "Positive affect", showed significantly negative correlations with the mean [oxy-Hb] changes mainly in the left hemisphere, whereas "Interpersonal problems" factor showed a significantly positive correlation with the size of NIRS activation predominantly in right prefrontal regions.

Conclusion: Our results indicate that remitted patients with MDD possibly have residual symptoms which are most likely to impair their social functioning and that these symptoms are differentially associated with brain function measured with NIRS.