Low-grade inflammation differentiates between symptoms of apathy and depression in community-dwelling older individuals

Background: Systemic low-grade inflammation has repeatedly been associated with depression in old age, but the relationship with apathy is less clear. The present study assessed whether C-reactive protein (CRP) is differentially associated with symptoms of apathy and depression. Methods: A population-based cohort study was carried-out. At baseline and after two and four years of follow-up, CRP levels were assessed and symptoms of apathy and depression were measured using the 15-item Geriatric Depression Scale. Logistic regression analysis was used to investigate the cross-sectional and longitudinal associations of CRP with symptoms of apathy and depression. Results: Two thousand forty-seven community-dwelling participants (70-78 years) without a history of cardiovascular disease or stroke were studied. A cross-sectional association was found between CRP and apathy symptoms at three time points (odds ratio (OR) per natural log unit increase in CRP: baseline visit = 1.40, 95% CI = 1.12-1.75; two-year follow-up visit = 1.62, 95% CI = 1.17-2.25; four-year follow-up visit = 1.51, 95% CI = 1.03-2.21). This did not change after adjustment for demographics and depressive symptoms, and was slightly attenuated after adjustment for cardiovascular risk factors. No cross-sectional association was found with depressive symptoms. Baseline CRP did not predict incident apathy or depressive symptoms during four years of follow-up. Conclusions: Increased CRP levels are associated with apathy symptoms but not with depressive symptoms. This suggests a differential effect of inflammation on apathy and depression. In older persons, symptoms of apathy may be a behavioral manifestation of concurrent low-grade inflammation.