Memantine Treatment in Alzheimer's Disease Patients

Inclusion Criteria: 1. Probable AD based on the diagnosis criteria of NIA-AA guideline (the U.S. National Institute on Aging and Alzheimer's Association guideline, McKhann et al, 2011\[8\]; 2. Male or female, 50 years and older ; 3. All inpatients or outpatients recruited into this study must meet MMSE score ≤24 points, patients with MMSE score as 21-24 points will be enrolled into mild group, patients with MMSE score as 10-20 points will be enrolled into moderate group, patients with MMSE score less than 10 points will be enrolled into severe group. 4. Have a reliable caregiver who can accompany the patient to the site to complete the required study procedures; 5. Provide the informed consent. Exclusion Criteria: 1. Patients with disturbance of consciousness of any causes; 2. Patients with severe aphasia or physical disability who were unable to complete neuropsychological examination; 3. Patients with mental illness; 4. Patients with a history of alcoholism and drug addiction, or traumatic brain injury, epilepsy, encephalitis, normal-pressure hydrocephalus and other neurological disorders causing cognitive impairment; 5. Patients with systemic diseases causing dementia (e.g. liver and kidney insufficiency, endocrine disorders, vitamin deficiency); 6. Patients with a history of ischemic or hemorrhagic cerebrovascular diseases, and vascular diseases (stroke foci) as confirmed by imaging examination; 7. Subjects who are unwilling or unable to abide by the study requirement.