Amyloid Imaging at UCSF

The following article was written by Linda L. Chao, Ph.D., Associate Adjunct Professor, Department of Radiology and Biomedical Imaging, UCSF and Henry F. VanBrocklin, Ph.D., Professor in Residence, Department of Radiology and Biomedical Imaging, UCSF

The FDA recently approved Amyvid (Florbetapir-F 18) for use in amyloid imaging in patients being evaluated for Alzheimer’s disease (AD) and other causes of cognitive decline. AD is the most common form of dementia, affecting almost half of the U.S. population over 85. Clinical signs of AD include cognitive impairments (particularly memory) and behavioral disturbances. Until recently, the only definitive way of diagnosing AD was by the presence of beta-amyloid plaques and neurofibrillary tangles, pathological hallmarks of the disease, in the brain at autopsy. Although doctors try to diagnose AD by taking the patient’s history and performing physical and mental status exams, 20% of dementia patients diagnosed with AD do not have plaques in their brains, a key component for the neuropathological confirmation of AD, at autopsy

Amyloid imaging basically involves injecting a “dye” that can get into the brain and stick to beta-amyloid plaques. When the “dye” is labeled with a radioactive isotope (such as fluorine 18) and used with a PET scanner, it is possible to see beta-amyloid plaques in a living person’s brain. As expected, amyloid imaging has shown that AD patients have a lot of plaques in their brains, older adults with normal memory function, generally, have little, if any plaques, and individuals with mild memory impairments have intermediate plaque levels.  Consistent with autopsy reports of plaques in the brains of individuals who died of non-AD causes and did not manifest symptoms of AD while they were alive, amyloid imaging has also shown that approximately 20 percent of “cognitively normal” seniors have evidence of plaques in their brains. This suggests that amyloid deposition occurs early in course of AD, beginning prior to the manifestation of disease symptoms. The FDA’s recent approval of Amyvid means that doctors may soon have a reliable way of diagnosing AD in patients with memory complaints while helping to rule out other forms of treatable dementia such as frontal temporal lobe dementia.

Although a large number of AD treatment trials are underway, none have been successful thus far. This has led to the suggestion that AD-modifying therapies may be most beneficial when used early in the disease process, before the onset of significant impairment. Therefore, amyloid imaging may supplement clinical evaluation in selecting patients for future anti-amyloid therapies. Detecting amyloid plaques in the brain may also be useful for determining whether anti-amyloid therapies actually work.

The approval of Amyvid also raises questions such as: How much will the imaging scans cost?  - Potentially $3,000 or more. Who will be able to get the scans? - Any older person concerned about AD. Are the scans worth getting given that there is currently no cure for AD? – It may confirm or rule out other forms of dementia. This is a very important advance that will benefit both patients and scientists.

For addition articles on Alzheimer’s disease, please see here.