No one knows what causes Alzheimer's disease.
Some research hints that a virus is the culprit.
Not everything that looks like Alzheimer's is Alzheimer's. Brain tumors, blood clots in the brain, severe vitamin B12 deficiency, hypothyroidism, and some drug side effects can mimic Alzheimer's disease. Sometimes medications to treat depression, paranoia and agitation can minimize symptoms, but they will not necessarily improve memory. It's especially helpful to put structure in the life of someone who's in the early stages of Alzheimer's. Post reminders on an oversized and prominently displayed calendar.