A topic that received a lot of attention at the University of California San Diego School of Medicine update on Alzheimer’s research was the use of Eli Lilly’s Amyvid for detection of amyloid beta deposits in the brain, one of the physical signatures of Alzheimer’s Disease. Dr. Gil Rabinovici, MD, a physician and researcher at the UC San Francisco Memory and Aging Center, provided an update on using Amyvid (florbetapir) PET tracer for amyloid imaging.
Dr. Rabinovici, a recognized expert on amyloid imaging, took the unusual approach of presenting a strong case against using imaging tests for many possible Alzheimer’s scenarios. This was a useful exercise, as it helped identify the cases in which Amyvid imaging would be especially helpful.
First, the positives on Amyvid: it’s reliable, with results for sensitivity and specificity in the 83% to 90% range. And this is for both visual (human) readings and quantitative (computerized) readings of imaging results. Amyvid also has the FDA’s stamp of approval as a diagnostic agent for brain imaging of amyloid plaques in patients. “Diagnostic” is the key word here: this is an example of a neuroscience research tool moving into the (specialist) doctor’s office.
The Problems with Amyvid Imaging for Amyloid Beta
So what are the drawbacks with Amyvid? There are several:
Very high rate of potential false positives. There are millions of healthy, cognitively normal older adults (age 65+) who have significant amounts of amyloid beta in their brains. An Amyvid scan could raise a false red flag with these individuals. (Read this article on why amyloid deposits may not be the proximate cause of AD.) Physicians and staff will need extensive training on how to correctly interpret Amyvid scan results, based on each individual patient’s health history, age, and cognitive profile.
It’s diagnostically accurate only in the narrowest sense. A positive Amyvid scan means confirmation of amyloid beta deposits in the brain. So what does this mean? If the scan is for a cognitively healthy 75 year old, the result might not mean much (see first drawback). Also, the Amyvid scan won’t differentiate between Alzheimer’s pathology and, say, Dementia with Lewy bodies (DLB), another form of dementia that includes amyloid beta in the brain.
Amyvid scans are very expensive. The current cost for Amyvid is $1,600 per dose, and that doesn’t appear to include the PET scanner time and staff overhead, so $3,000 – $4,000 per scan is probably a good “all in” number. Medicare is being petitioned to approve and pay for Amyvid scans – no word yet on whether they will sign up for this. Given the 60+ Million potential Medicare beneficiaries who could start receiving advertisements for “brain health scans” and the like, the potential for abuse and cost to the US taxpayer is enormous.
Dr. Douglas Galasko, MD, Director of the Shiley-Marcos Alzheimer’s Disease Research Center at UCSD, mentioned during his talk that he worries a bit about “drive thru” imaging and biomarker commercial enterprises, that are heavy on technology but light on clinical experience and judgment. Given the costs of these new imaging techniques, this is a valid concern.
When Amyvid Scans Make Good Sense
Back to the positive. There are definitely cases when Amyvid scans can be very helpful and prescient. The general profile on when to use this technology includes the following:
Cognitive impairment in middle aged (< 65 years) patients. The prevalence rates for Alzheimer’s Disease in people who are in their 50s or early 60s is quite low – less than 1%. If noticeable cognitive problems are present in a 55 year old, then an Amyvid scan can help confirm or rule out early onset Alzheimer’s Disease.
The Amyvid scan could also potentially help point to (but not diagnose) other considerations such as corticobasal syndrome, posterior cortical atrophy, and a host of other rather esoteric neurological conditions with this middle aged patient.
In general, Amyvid is a good addition to a very thin list of diagnostic tools for Alzheimer’s Disease, if it is used selectively with patient age and symptoms in mind.
Cognitive screening tools, such as computerized cognitive assessments, can also be useful in clinical settings. Medicare instituted a new preventive health benefit known as the Annual Wellness Visit (AWV), which includes a loosely defined “detection of any cognitive impairment”. This wellness visit could act as a large platform to move (cost effective) cognitive health screening into primary care offices.