Recently, I spoke to a group of medical students about Alzheimer’s disease. I have been giving these talks three or four times a year for the last five years now. I know a lot about Alzheimer’s disease because I am a retired neurologist, and I have treated many patients with dementia, including Alzheimer’s disease. I also know a lot because now I have mild Alzheimer’s dementia. As we’ll see in Chapter 3, Alzheimer’s dementia is the late stage of Alzheimer’s disease when cognitive impairment interferes with activities of daily living. The pathological changes in the brain caused by Alzheimer’s disease begin to appear up to 20 years before the onset of cognitive impairment.