This is where amyloid imaging could be the most clinically helpful, Dr. Caselli said.
"In my opinion, the use of amyloid PET will be most important for this indication. Younger patients are employed, have families they are supporting, and usually present early in their course when psychiatric pathology may be suspected. Imagine the 52-year-old who receives a poor job review and states he is unable to understand the new software or recall a client’s name, and seeks medical attention with the implication of disability hanging in the balance. Such a patient will not appear physically ill and is not generally suspected to have Alzheimer’s disease, but when current clinical methods indicate mild cognitive impairment, an amyloid PET scan could solidify the organicity of the diagnosis."
Clinical situations in which not to test
The document’s seven contraindications spell out scenarios in which amyloid imaging is unhelpful. These include:
• Patients who meet both the clinical criteria for Alzheimer’s and the typical age of onset. The potential benefit of detecting amyloid pathology probably would not alter patient management.
• Determining dementia severity. There’s no indication that amyloid burden correlates with symptom severity.
• Relying on reasons based solely on family history or positive apolipoprotein E–epsilon 4 status.
• Investigating a clinically unconfirmed cognitive complaint.
• Using this imaging instead of genotyping patients who have a suspected autosomal mutation.
• Making disease predictions in cognitively normal older adults
• Testing for any nonmedical use, such as for medicolegal, disability, insurance, or employment-related issues.
Patients who undergo the imaging procedure need to understand its benefits and its limitations, the task force said. Amyloid plaques don’t always mean Alzheimer’s disease is present. For example, 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 AD, but also in other medical conditions," such as Lewy body dementia and amyloid angiopathy, the document noted. The scan can’t differentiate these, and it is not useful when evaluating patients with frontotemporal dementia.
But amyloid imaging does confer a number of benefits when used appropriately, according to the task force. Whether the result is positive or negative, it furthers clinical decision-making in appropriately selected patients. It can guide medication management by getting patients on the right drugs faster and keeping them off those that won’t help. The results can shape other diagnostic investigations in the same way by letting patients avoid unnecessary tests or proceed to more informative ones.
There is much benefit in "the value of knowing" amyloid PET scan status, the document noted. About 25% of dementia cases can have reversible causes, like depression or vitamin B12 deficiency. And U.S. surveys have shown that most Americans would prefer to know if their symptoms could be caused by Alzheimer’s so that they can make independent decisions about the future.
But "what such polls often fail to mention are 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."
Dr. Johnson and some of the other task force members reported multiple relationships with drug companies. Dr. Caselli has no financial disclosures.