Identifying a subset of older persons with specific chronic medical conditions at high risk for poor outcomes of major depression is important in order to enhance the treatment for depression in primary care. The principal finding of this study was that chronic pulmonary disease and vascular disease were associated with low remission and response rates of depression during the early phases of follow up in older patients receiving usual care, while comorbid cognitive impairment was associated with a less stable remission in usual care. Importantly, no medical illness or cognitive disorder influenced the remission and response rates of depression in patients of primary care practices implementing PROSPECT's intervention. The intervention appears, at least in part, to overcome the effects of medical comorbidities.
Before discussing our findings, the results must first be considered in the context of some potential study limitations. First, we obtained our results only from primary care sites in greater New York City, Philadelphia, and Pittsburgh, whose patients may not be representative of other primary care practices in the United States. However, the participating practices were diverse and consisted of community-based urban and rural practices of varying sizes as well as academically affiliated practices. Second, there is the potential for all the sources of error associated with retrospective interview data including imperfect recall and response bias. Third, selection bias is a potential limitation because, although the larger project was based on a random sample of primary care patients, the data on medical comorbidity and clinical remission of depression consisted of all who were selected for the larger project, agreed to participate, and had complete information. Fourth, although more frequent follow-up would have been desirable, concerns about participant burden and cost led us to select few, yet clinically meaningful, follow-up times. Finally, treatment may have changed frequently both in the intervention and the usual care practices and our analyses do not account for change in treatment.
Nonetheless, despite limitations our results deserve attention because we attempted to evaluate the effect of different chronic medical conditions on outcomes for major depression in primary care. Our results are not wholly consistent with our initial hypotheses. Summarizing our findings relating to our first aim, we observed four distinct patterns for the effect of medical conditions on depression outcomes. Most conditions had no impact on outcomes. Some conditions, such as myocardial infarction and atrial fibrillation in usual care, were associated with improved outcomes. Conversely, vascular disease in usual care was associated with worse outcomes. Chronic pulmonary disease in usual care was associated with delayed remission or response. Finally cognitive impairment in usual care was associated with a less stable response, with outcomes comparable to those for other patients over the short term, but with a worse response over time. By contrast, the depression outcomes for patients in the Intervention Condition did not significantly differ among persons with and without specific medical illnesses, regardless of the outcome criterion.
The reasons for our findings are not entirely clear. The differences in depression outcomes might be due to the different nature of the medical conditions with some presenting as episodic events, e.g. myocardial infarction and atrial fibrillation, and others which have ongoing symptoms, e.g. chronic pulmonary disease. Our findings of lower rates of response seen with vascular disease which approached but did not reach statistical significance in our final models are consistent with the studies by Alexopoulos and colleagues on vascular depression [18
]. Overall the findings support the hypothesis that specific medical conditions may influence depression outcomes in Usual Care but the mechanisms have yet to be fully understood. There may be unmeasured biological, psychological, and social mechanisms that are important in explaining the effect of medical conditions with ongoing symptoms versus medical conditions presenting as episodic events on treatment outcomes for depression in Usual Care.
The second aim of our research was to examine whether the assignment to PROSPECT's Intervention Condition or Usual Care modified the relationship between the presence of a chronic medical illness and outcomes for depression. The only significant interaction between the disease effects and treatment assignment was for atrial fibrillation, where the probability of remission appeared to be greatest in usual care participants with the condition. This observation is difficult to explain, and we cannot exclude the possibility that one interaction out of the large number tested may have appeared to be significant by chance alone. In general, the findings seem to indicate that the effects of medical conditions are apparent in the Usual Care sample, but that they are not significant in the Intervention Condition. For example, a history of MI appeared to increase the rate of response in usual care patients up to that observed in the Intervention Condition. Cardiac disease may represent a “wake-up call” for usual care patients and providers, leading them to focus more carefully on the treatment of depression. In contrast, the delayed response in chronic pulmonary disease may have occurred because chronic pulmonary disease interfered with the management of depression. In addition, the loss of response in individuals with cognitive impairment in Usual Care may have also occurred because cognitive impairment interfered with the management of depression beyond the initial treatment phase. Consistent with these explanations, the lack of significant effects of the illnesses in Intervention patients suggests that the Intervention can, at least in part, overcome the effects of medical comorbidity. Our results are consistent with other studies that found an attenuation of the effect of medical comorbidity on depression outcomes in depression interventions using measures of total medical comorbidity, not specific medical conditions [32
Late life depression often presents in primary care patients with medical comorbidity. We found that certain chronic medical conditions may play a role in depression outcomes among primary care elders but the effect of specific medical comorbidity may be overcome by care management. Our results suggest trained depression care managers combined with algorithm-based care can attenuate the effects of medical comorbidity. Therefore, such interventions can improve the quality of care for late life depression where medical comorbidity is common. Interventions designed to improve depression treatment, to be sustainable and acceptable to physicians and patients, must account for the medical comorbidity that commonly accompanies depression in older persons. Identifying patients with specific chronic medical conditions who will benefit most from special attention may be key to improving outcomes for depression in primary care. The integration of treatment for depression with the treatment for specific medical conditions should be considered.