Progression Delaying Effect of Escitalopram in Alzheimer's Disease

Inclusion Criteria: * Age:40\~90 years * Education:not illiterate * Clinical Dementia Rating (CDR):0.5\~2 * Modified Hachinski Ischemic Score (Rosen et al., 1979):less than 4 * Dementia according to DSM-IV criteria * Probable Alzheimer's disease according to NINCDS-ADRDA criteria * Current ongoing donepezil medication at stable doses (5 \~ 10 mg/day) for at least 2 months Exclusion criteria: * Evidence of delirium, confusion or altered consciousness * Evidence of Parkinson's disease, stroke, brain tumor and normal pressure hydrocephalus * Evidence of infectious or inflammatory brain disease * Evidence of serious cerebrovascular diseases * Current major depressive disorder or other major psychiatric illnesses * Evidence of serious or unstable medical illnesses which can significantly change cognitive state * History of alcohol or other substance dependence * Any antidepressant medications within the previous 4 weeks * Absence of a reliable and cooperative collateral informant * Any conditions which prohibit MRI scan, such as presence of pacemaker or cerebrovascular clip, and claustrophobia * Evidence of focal brain lesions on MRI including lacunes and white matter hyperintensity lesions of grade 2 or more by Fazeka scale