Bret S. Stetka, MD


April 01, 2013

In This Article

Should You Order Amyloid Imaging?

Dr. Rabinovici closed out the session with a practical look at the benefits and drawbacks of amyloid beta imaging. From a purely diagnostic perspective, knowing a patient's amyloid status appears valuable. As many as 82% of amyloid beta-positive patients ultimately convert to full-blown AD vs only 0%-7% of amyloid beta-negative patients. When FDG-PET findings are included, amyloid imaging is even more predictive, as Dr. Frisoni presented.

False positives are a concern, however; 20%-40% of elderly people not diagnosed with AD have amyloid plaques at autopsy. Then there is the exorbitant cost of imaging every patient with potential AD; at $1600 a scan and with 450,000 AD cases diagnosed every year, total annual costs of the procedure would climb to a staggering $720,000,000. But amyloid imaging has demonstrated utility in various clinical scenarios, suggesting that, in certain cases, it is worth considering.

The Society of Nuclear Medicine and Molecular Imaging and the Alzheimer's Association Amyloid Imaging Taskforce recently released appropriate-use criteria[3] recommending amyloid imaging in the following cases: (1) patients with cognitive complaints and objectively confirmed impairment; (2) patients in whom diagnosis is uncertain (with AD being a possibility) after comprehensive evaluation by a dementia expert; and (3) the knowledge of amyloid beta status is expected to increase diagnostic certainty and alter management.

Dr. Rabinovici then walked through clinical scenarios in which to apply the criteria, including patients with persistent or progressive unexplained mild cognitive impairment; patients with possible AD, such as those with an atypical clinical course; and those with significant comorbidities, such as vascular or psychiatric disease or substance abuse. He recommended not using the criteria at initial patient evaluations -- "[imaging is] not a substitute for a clinical exam" -- or when screening cognitively normal patients, with his accompanying slide shouting, "Preclinical AD is a research concept only!" The nonmedical use of imaging, such as in cases of disability or unemployment evaluations, is not recommended, nor is imaging done on the basis of genetic risk or family history of AD.

Dr. Rabinovici also reviewed clinical situations in which amyloid beta imaging is simply not useful. These include differentiating AD from other diseases in which amyloid beta deposition can be present, such as dementia with Lewy bodies; determining dementia severity; and situations in which imaging is unlikely to add value, namely straightforward clinical AD phenotypes.

Then came the big questions: Should society pay for amyloid scans? And what is the value of improved diagnosis given the limited efficacy of currently available therapies? Having already discussed the drawbacks of amyloid beta imaging -- the false positives, the costs, the potentially minimal impact on patient outcomes -- Dr. Rabinovici presented rationale in support of imaging, including the hidden costs of diagnostic uncertainty: second and third opinions, unnecessary imaging and lab tests, unnecessary treatments (eg, cholinesterase inhibitors in cases of frontotemporal dementia), and the value and peace of mind that patients and families may feel by simply having a diagnosis. From a therapeutic standpoint, he noted, amyloid beta imaging probably will also play a critical role in future drug development.

Overall, the presenters admitted that the idea of ordering biomarkers in cases of suspected AD remains somewhat controversial. As critics will point out, a more accurate AD diagnosis provides little benefit to patients given the modest efficacy of current therapies. However, the panel collectively regarded biomarker data, at least in research settings, as a valuable asset, ultimately improving the pathophysiologic understanding, diagnosis, and management of AD. Leaving the session, Dr. Jacques Hugon, a neurology professor from Saint-Louis Lariboisière Fernand-Widal University Hospital in Paris, who is studying the clinical use of AD biomarkers, commented to Medscape, "At my university, we order biomarkers on almost all of our suspected AD patients."