Influence of Comorbid Depression on Mortality among SSDI-eligible Medicare Beneficiaries with Chronic Obstructive Pulmonary Disease

Abstract

Background: Chronic obstructive pulmonary disease (COPD) is a condition with high mortality and morbidity. Comorbid depression can place COPD patients at increased risk of adverse outcomes. Although both COPD and depression are associated with significant morbidity, to date few studies addressing COPD-related outcomes have included individuals who receive Social Security Disability Insurance (SSDI). Objectives: To examine the influence of comorbid depression on mortality among a nationally-representative sample of Medicare beneficiaries suffering from COPD by SSDI-eligibility status. Methods: This retrospective cohort study used a 5% random sample of the 2006-2008 Chronic Condition Warehouse administrative data. The study cohort included 93,019 Medicare beneficiaries diagnosed with COPD who lived through 2006 and were continuously enrolled in Medicare Parts A, B, and D. Two-year (2007-2008) all-cause mortality was the study outcome. Comorbid depression was measured in 2006-2008. SSDI-eligibility was defined using the original reason for Medicare entitlement. Multivariable generalized estimating equations models estimated the association between SSDI-eligibility and depression, as well as the modification effect of SSDI-eligibility on their relationship. Survival analyses using extended Cox proportional hazards models further estimated risk of death from depression and antidepressant treatment among beneficiaries aged 65 and older (n=75,699) by SSDI-eligibility. Results: About two-fifths (39.4%) of beneficiaries with COPD had a depression diagnosis in 2006-2008; of those, 79.5% received antidepressant treatment. SSDI-eligibility was not only associated with a 12% (95%CI=10%,15%) higher likelihood of depression but also modified factors in regard to depression diagnosis and receipt of antidepressant treatment. COPD beneficiaries with a baseline depression diagnosis had a higher risk of death (HR=1.13; 95%CI=1.09, 1.18) in non-SSDI-eligible beneficiaries. Those who received antidepressant treatment had reduced risk of death, with greater benefits on mortality in SSDI-eligible than non-SSDI-eligible beneficiaries. Conclusions: This study provides the first evidence suggesting that SSDI-eligibility is not only associated with higher likelihood of having a depression diagnosis, but also is a significant effect modifier of the relationship between antidepressant treatment and mortality in Medicare beneficiaries with COPD. Findings demonstrate the benefits of antidepressant treatment on mortality in both SSDI-eligible and non-SSDI-eligible beneficiaries. In practice, clinicians should consider timely antidepressant treatment to improve outcomes for this population.