Levels of inflammatory markers have been found to be significantly associated with major depressive disorder (MDD) and cognitive impairment. The aim of this study was to investigate whether the level of C-reactive protein (CRP) is correlated with depressive mood and cognitive impairment in MDD patients. In 149 subjects with MDD, the 21-item Hamilton Rating Scale for Depression (HAM-D), Continuous Performance Test (CPT), Finger-Tapping Test (FTT), and Wisconsin Card-Sorting Test (WCST) were administered before and after antidepressant treatment. Besides, the level of CRP was measured. After 6weeks of treatment, the total HAM-D scores decreased significantly. In addition, the subjects' performance in the masked CPT and the WCST with completed categories significantly improved (p<0.001 and p=0.027, respectively) after the reliable change indices were corrected for practice effects. The CRP levels had increased significantly after six weeks of treatment after adjustment for age and gender (p<0.001). In addition, the CRP levels remained significantly high after six weeks of treatment in patients with a higher baseline level (r=0.657, p<0.001). Although the association between baseline CRP level and HAM-D score was not significant, the baseline CRP level was significantly correlated with treatment response at week 2 (r=0.327, p=0.020). The baseline CRP level was also negatively correlated with performance in the FTT before treatment (r=-0.580, p=0.006). Moreover, the baseline CRP level was significantly correlated with performance in the FTT (r=-0.501, p=0.021) and WCST with completed categories (r=-0.521, p=0.015) at week 6. The cognitive function of patients with high baseline CRP levels might remain impaired even if their mood symptoms improve after antidepressant treatment. Whether adjunctive anti-inflammatory medication may help to preserve cognitive function merits further investigation.
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