In 2020, Alzheimer's Disease International estimated that the number of people living with dementia worldwide - nearly 55 million in 2020 - will almost double every 20 years.There is no single test that can show if a person has Alzheimer's, but doctors can almost always determine if a person has dementia, although it may be difficult to determine the exact cause. Diagnosing Alzheimer's requires careful medical evaluation, neurological testing, and sometimes brain imaging and blood tests to rule out other causes of dementia.Most of the testing for early disease - MRI scans of the brain, brain P...