Amyloid beta is the most widely recognized marker of Alzheimer Disease (AD), and many even believe it is a causal factor. Amyloid plaques are associated with neuronal damage that can eventually lead to profound dementia in a subset of patients. For patients with dementia, the standard imaging work-up has been MR and FDG-PET imaging of the brain. These diagnostic studies often help to establish the diagnosis of AD by distinguishing it from other conditions such as fronto-temporal dementia. However, these studies are less useful early on in the disease, at a time when treatment modifications may still be effective.
Clinical guidelines require the presence of dementia to make the diagnosis of AD. However, by then, it may be too late to halt or even delay the progression with treatments aimed at reducing amyloid deposition. The recent FDA approval of F18-Florbetapir, an amyloid tracer and imaging biomarker, is a giant leap forward.
As with any diagnostic test, amyloid imaging carries with it the expectation of increased diagnostic certainty, or at least the potential to alter medication choices and regimens, and/or improve patient understanding and motivation. The strength of amyloid imaging lies in its high negative predictive value. Its best use is when the presentation is atypical or when someone has an early-onset and objectively verified cognitive decline. This is where MR imaging and FDG-PET fall short. Amyloid scanning should neither be the front-line imaging study for elderly patients with cognitive decline nor a screening test for AD.
It is important to emphasize that amyloid deposits in the brain do not automatically equate to Alzheimer disease. With the appropriateness criteria and indications for amyloid scanning now established, CMS should work swiftly to approve reimbursement. Research can then be appropriately directed at drug development strategies for amyloid removal or perhaps even methods for preventing amyloid deposition in the first place.
Read “Amyloid PET Imaging Plays Pivotal Role in Alzheimer’s Care.”
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