Should Brain Scans Diagnose Dementia?

Alzheimers disease taskforce urges caution when using PET imaging to diagnose dementia

(RxWiki News) Dementia causes changes in the brain. But should brain imaging be used to diagnose Alzheimer’s disease? Experts say that doctors should use imaging cautiously.

A task force of dementia experts looked over all the studies that used positron emission topography (PET) to look for proteins of Alzheimer's disease in the brain.

They concluded that PET scans can be useful but should not replace clinical testing. For example, PET scans can help confirm a diagnosis, but they should not be used to determine the severity of Alzheimer's.

"Ask a doctor which dementia tests are right for you."

The task force was made up of doctors and researchers who are experts in dementia. They looked at published studies with the goal of creating a set of guidelines for how PET imaging of beta amyloid should be used.

Beta amyloid is a protein that builds up in the brains of people with Alzheimer's disease. However, many elderly people show signs of beta amyloid build up in the brain, even though they don’t have dementia. Because the relationship between beta amyloid plaques and Alzheimer's is not well understood, the task force created some guidelines for the best use of PET imaging.

People who might be candidates for beta amyloid PET imaging are:

  • Those with chronic and progressing mild cognitive impairment
  • Those who have Alzheimer's symptoms but also symptoms of other dementias
  • Those who are under the age of 65 and show progressive dementia symptoms

In these people, PET imaging can help doctors to determine if dementia symptoms are those of Alzheimer's or some other form of dementia, like vascular dementia. Separating Alzheimer's disease from other forms of dementia is important because it helps doctors to choose the best treatment options.

The task force recommended that PET imaging for beta amyloid should not be used for:

  • Patients whose symptoms are typical of Alzheimer's disease
  • Determining severity of Alzheimer's disease
  • People whose cognitive complaints have not been confirmed by clinical tests
  • People with no symptoms
  • Non-medical reasons, like legal or insurance testing

PET imaging for Alzheimer's disease can show the amount of plaques in the brain. But having plaques does not necessarily mean a person has Alzheimer's. Patients who have no symptoms or whose symptoms are not showing up on clinical memory tests may have plaques in the brain but not have Alzheimer's disease. So the imaging test could give a false diagnosis.

Also, having more plaques does not mean more severe Alzheimer's disease. So PET imaging cannot show how severe a person’s dementia is.

The task force also cautioned that PET amyloid imaging should not be used when types of dementia other than Alzheimer's - such as frontotemporal lobar degeneration or vascular dementia - are suspected.

The task force concluded that PET imaging can help doctors better choose treatments and other tests. The relationship between beta amyloid and Alzheimer's is still unclear, so caution should be used with this testing.  The task force urged that PET imaging should not be the only deciding factor in a diagnosis of Alzheimer's disease.

The task force summary report also cited the patient’s value of knowing as a good reason to use imaging to confirm a diagnosis of Alzheimer's. A poll showed that 89 percent of Americans said they would want to know for sure because it gives them the chance to plan for the future.

This study was published in January in Alzheimer’s & Dementia. Members of the task force and reviewers for the studies reported affiliations with multiple pharmaceutical and biotechnology companies.

Review Date: 
January 31, 2013