A longitudinal study of Alzheimer's disease: rates of cognitive and functional decline

To measure rates of decline in cognition and function in patients with Alzheimer's disease (AD) and to investigate their accelerating risk factors in Korea.

This study presents longitudinal data on a community-based sample of 107 patients with AD, followed at 6 months and 12 months. The cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-cog), the Mini Mental State Examination (MMSE) and the Disability Assessment for Dementia Scale (DAD) were given. Mixed model analyses were conducted using the following independent variables: times of repeated assessment (0, 6 or 12 months), severity of dementia assessed by the Functional Assessment Staging (FAST) and individual indicators as covariates.

Average annual rates of decline in the MMSE, the ADAS-cog and the DAD were 2.3, 11.4 and 15.1 points, respectively. Neither gender, duration of formal education, nor duration of AD since onset was significant predictors of cognitive and functional decline. Patterns of functional decline in total DAD, instrumental ADLs, planning and organization and performance subscale are linear as MMSE score declines, while those of the basic ADLs and the initiation are curvilinear.

This naturalistic observational study measured rates of cognitive and functional decline in AD, and can provide reference data for further longitudinal studies or clinical trials. Further study will be necessary to determine whether linear or curvilinear pattern in functional decline is due to progression of AD itself or statistical artifact.