COGNITIVE PERFORMANCE AND THE TEMPORAL COURSE OF DEPRESSIVE SYMPTOMS OVER SEVEN YEARS' FOLLOW-UP: THE SMART-MR STUDY

Abstract

Depressive symptoms frequently occur in patients with cognitive decline and Alzheimer's dementia, but their interactive relationship is complex and the direction of causation is still a topic of research. We examined the temporal course between cognitive performance at baseline and biannually assessed depressive symptoms over seven years of follow-up in non-demented patients with symptomatic atherosclerotic disease. We used data of 736 patients (mean age 62±10 years; 82% male) of the SMART-MR study with neuropsychological assessment on four cognitive domains at baseline and at least one measurement of depressive symptoms. Depressive symptoms were assessed with the Patient Health Questionnaire-9 at baseline and biannually during seven years of follow-up. The PHQ-9 assesses presence of the nine DSM-IV symptoms for major depressive disorder in the past 2 weeks. GEE models, adjusted for age, sex, educational level and DART-score, were used to assess the association between baseline cognitive performance (on the domains memory (MEM), working memory (WMEM), executive functioning (EXEC), and information processing speed (SPEED)) with depressive symptoms at multiple time points during follow-up. An interaction term between the respective cognitive domains and time as dummy variable for each time point was included to examine the temporal relationship. Median (10th-90th percentile) score on the PHQ-9 was 2 (0-8) at baseline and the overall response on the repeated PHQ-9 assessments varied between 86% and 97%. Because GEE analyses showed no significant interactions between the respective cognitive domains and time (interaction p-value MEM=0.79; WMEM=0.89; EXEC=0.52; SPEED=0.65) we repeated the analyses without the interaction terms. These analyses showed that a z-score decrease in MEM, EXEC or SPEED, but not WMEM, was significantly associated with more depressive symptoms averaged across all time points (B (95%CI): 0.70 (0.35; 1.05) for MEM, 0.88 (0.41; 1.36) for EXEC, and 0.57 (0.21; 0.92) for SPEED).