Report Outlines Amyloid PET Imaging Criteria for Alzheimer's Disease

Clinical Situations in Which Imaging Is Unnecessary
The criteria also included the following seven clinical scenarios in which amyloid imaging is very likely to be unhelpful:

• • When patients meet the clinical criteria for Alzheimer’s disease and are at the typical age of onset. The potential benefit of detecting amyloid pathology probably would not alter patient management, according to the criteria.

• • When determining dementia severity. No evidence indicates that amyloid burden correlates with symptom severity.

• • When reasons for imaging are based solely on family history or positive apolipoprotein E e4 status.

• • When investigating a clinically unconfirmed cognitive complaint.

• • When imaging would be used instead of genotyping for patients who have a suspected autosomal mutation.

• • When predicting disease in cognitively normal older adults

• • When testing for any nonmedical use, such as for medico-legal, disability, insurance, or employment-related issues.

Patients who undergo the imaging procedure should understand its benefits and its limitations, said the task force. Amyloid plaques do not always indicate Alzheimer’s disease. As age increases, so does the likelihood of amyloid deposition, even in cognitively normal people. “Another major caveat is that a positive amyloid scan can also be seen in not only [Alzheimer’s disease], but also in other medical conditions,” such as Lewy body dementia and amyloid angiopathy, according to the criteria. The scan cannot distinguish between these conditions and is not useful when evaluating patients with frontotemporal dementia.

Knowing his or her amyloid PET scan status can have clinical benefits for the patient, according to the criteria. About 25% of dementia cases have reversible causes, such as depression or vitamin B12 deficiency. Surveys indicate that most Americans would prefer to know whether their symptoms could be caused by Alzheimer’s disease so that they can make independent decisions about the future.

But “what such polls often fail to mention is the number of people who would suffer psychological harm if they received bad news from such testing,” Dr. Caselli cautioned. “In another poll we have been conducting, more than 10% of patients stated they would ‘seriously consider suicide’ if they found there was biomarker evidence of preclinical Alzheimer’s disease. This is a powerful diagnostic modality, but one in which implications of results are not fully understood. What we offer our patients, therefore, must be limited to the scenarios the committee has described, at least until we have much more experience and understanding of the implications and reliability of test results.”