The current project sought to identify baseline factors related to major depression outcome in older primary care patients enrolled in mental health treatment. Results indicated that baseline anxiety disorder, female sex, increased medical comorbidity, and baseline depressive symptom severity independently predicted non-remission at six months. Clinically, these findings are significant as they point toward the added challenge in treating depression within primary care when accompanied by psychiatric and medical comorbidity. Given the negative health consequences associated with depression, failure to attain remission following mental health treatment places these patients at an even greater risk for additional morbidity and possible mortality.
This study expands the previous literature by defining remission in major depression as the absence of DSM-IV diagnostic criteria for any
depressive disorder. Classifying remission according to criterion symptoms is clinically significant as even residual symptoms of depression have been linked with shorter time to relapse and impaired functioning, even in the elderly (Chopra et al., 2005
; Cui et al., 2008
). This criteria is not only more stringent, but serves as a good goal for treatment. However, our finding that depression severity was an independent predictor of remission suggests that a baseline measure of depression severity is beneficial in determining the possibility of remission. Thus, while only using DSM-IV criteria for the diagnosis of major depression in older primary care patients may describe who has depression, it will likely miss the opportunity to identify patients who will not remiss and require additional care due to a more severe depression.
Additionally, our finding linking comorbid anxiety and non-remission in major depression is consistent with some (Steffens and McQuoid, 2005
), but not all previous research (Lenze et al., 2003
). In a naturalistic study of older adults receiving treatment for depression and comorbid symptoms of generalized anxiety disorder, Steffens and McQuiod (2005)
found the presence of generalized anxiety disorder (GAD) symptoms to be associated with a longer time-to-remission, when compared with depression alone. Similarly, in a separate study, older adults receiving pharmacotherapy and interpersonal psychotherapy for the treatment of major depression were found to have slower rates of response when also presenting with elevated levels of anxiety (Andreescu et al., 2007
). Participants with comorbid anxiety were also more likely to have a recurrence of depression within two years. While the aforementioned studies found comorbid anxiety to be linked with poorer outcomes in older adults with depression, Lenze and colleagues (2003)
failed to find differences in rates of response in older adults with and without comorbid anxiety receiving treatment for depression. While these mixed findings point toward the need for additional research in comorbid anxiety and depression, particularly in later life, our results suggest that the presence of anxiety needs to be assessed at baseline in patients who are being initiated on treatment for major depression.
These findings need to be highlighted in the demographic and ethnic diversity of the enrolled population. While 63% of the study sample was non-Caucasian, we found no differences in remission from DSM-IV depression with respect to ethnicity. This is consistent with a prior PRISM-E project that examined differences in service use and outcome, as defined by CES-D scores (Areán et al., 2008
). Our finding is novel and extends this previous work by examining race differences in DSM-IV major depression outcome within a diverse sample. The current project’s finding that women were less likely to achieve remission than men is consistent with some studies (Thase et al., 2005
), though others have failed to identify gender differences in treatment response (Quitkin et al., 2002
). Our results are surprising given that previous research has shown older men to utilize less mental health care than women in the treatment of depression (Unützer et al., 2003
). That said, the finding of female sex as a predictor of non-remission needs to be interpreted cautiously as female sex and education (i.e., less than 12 years), which was found to differentiate remission from non-remission in bivariable analyses, were highly correlated.
This study has several strengths. First, the study utilized a large, ethnically and geographically diverse sample of older primary care patients in the PRISM-E dataset, thereby making the results more generalizable. Second, the use of the MINI provided a standardized structured diagnostic psychiatric interview to assess for major depression and additional psychiatric disorders including anxiety and other depressive disorders. Further, in using the MINI to define outcome rather than a percentage decline on the CES-D, we adhered to DSM criteria while also extending the work of previous PRISM-E projects. Finally, while enrollment was restricted to those not in treatment at baseline, only 18 of 1,048 (1.7%) patients with major depression at enrollment were receiving current mental health or substance abuse treatment, thereby precluding them from study participation. The PRISM-E, however, did successfully target and improve access to treatment for a vulnerable group that historically did not receive mental health care (i.e., older adults). As a result, the initial treatment (of either arm) was likely to improve the baseline mood disorder in this study sample.
The findings should be interpreted in light of the study's limitations, which stem primarily from its design of re-examining data from a project that has already been conducted. First, given that remission was defined according to depression status at one point only (six months), it is possible that patients reaching remission prior to six months may have relapsed by the assessment period, thereby not being considered in remission for purposes of the current study. Similarly, some patients categorized as non-remitters may vary from other non-remitters based on a cyclical pattern of depression status. Further, the study was unable to investigate the role of cognition, particularly executive function, on depression outcome, as the PRISM-E screened out those with cognitive impairment. This is particularly important given that executive dysfunction has been previously linked with depression, medical comorbidity, and treatment response in depression (Alexopoulos et al., 2000
; Lockwood et al., 2002
). Another limitation is the use of self-report to quantify general medical illness burden, though previous research has demonstrated good agreement between self-report and medical record review of general medical illness (Bush et al., 1989
). Because those who did not follow up were more likely to be male and African-American, our final cohort may not be representative of this subgroup. Further, it may be that those lost to follow up were less sick and therefore less likely to follow through with treatment. Finally, it is entirely possible that other unstudied factors (e.g., social support, socioeconomic status, access to health care) may influence the association with non-remission in major depression than the variables examined in the current project.