FAQ: If Alzheimer's Is So Common, Why Isn't It Easier to Diagnose?

A fellow caregiver asked...

If Alzheimer's is so common, why isn't it easier to diagnose?

Expert Answer

Dr. Leslie Kernisan is the author of a popular blog and podcast at BetterHealthWhileAging.net. She is also a clinical instructor in the University of California, San Francisco, Division of Geriatrics.

It's difficult to diagnose Alzheimer's dementia for several reasons:

  • It can take time for the doctor to collect enough information to confirm the presence of permanent thinking problems that are bad enough to affect day-to-day function. Doing this usually requires some cognitive testing, as well as getting information from people other than the patient.

  • The doctor must make sure that the symptoms aren't being caused by one of the many other medical problems that can cause dementia symptoms. Often, doctors find that a person is suffering from probable Alzheimer's disease along with another problem, such as depression or a medication side effect. Non-Alzheimer's problems must be treated before a doctor can figure out whether there is also Alzheimer's and, if so, how advanced it is. (It's also common for people to have two causes of dementia at the same time, such as Alzheimer's disease and vascular dementia; this is called "mixed dementia.")

Until recently, the only way to definitely know if Alzheimer's disease was affecting a person's brain was to get a brain biopsy, or to examine the brain during autopsy. Exciting new tests now can detect Alzheimer's biomarkers in spinal fluid or on special brain imaging. However, these tests aren't yet available for routine practice. They also can't rule out the many other causes of memory problems and other dementia symptoms.

Barring a brain biopsy or autopsy, until recently Alzheimer's disease could only be diagnosed if a person had symptoms of dementia. However, the new biomarker tests for Alzheimer's have led experts to recognize a phase known as "preclinical Alzheimer's".