Although depression is a common co-morbid disorder in patients with mild cognitive impairment (MCI), not all patients with MCI exhibit depressive symptoms. This study aimed to investigate the effect of depression on cognitive and functional decline in MCI.

281 patients with MCI (MCI) defined by 0.5 score on Clinical Dementia Rating were included in the study. Patients were divided into three groups based on their Geriatric Depression Scale (GDS) scores: MCI without depression (GDS<10, n=50), MCI with mild depression (GDS10~19, n=120), and MCI with severe depression (GDS>20, n=111). Cognitive function tests (cognitive domains in CERAD-K including letter fluency, trail making test-A and B, and verbal learning test) and Blessed Dementia Scale-Activities of Daily Living (BDS-ADL) were measured. Group differences were analyzed using an analysis of variance (ANOVA). Correlation between GDS scores and BDS-ADL were analyzed.

An ANOVA test showed that activities of daily living differed significantly across groups (F(2, 276) = 13.53, p<0.001). Post-hoc analysis showed MCI with severe depression had a significantly higher mean BDS-ADL score compared with both MCI without depression and MCI with mild depression (both, p<0.001). Correlation analysis showed significant positive correlation between GDS and BDS-ADL (r=0.366, p<0.001). However, mean scores of cognitive function tests were not different among three groups.

The present study suggests that co-morbid depressive symptoms may have negative impact on functional status in patients with MCI. This may further suggest the importance of evaluation and treatment of depressive symptoms in patients with MCI.