What is beta amyloid and how is it implicated in Alzheimer’s disease?
Beta amyloid protein "plaques" in the brain are one of the defining features of Alzheimer's disease. However, we also know the effects of beta amyloid on a person’s brain and cognitive abilities are not straightforward. For example, research has shown that up to a third of older people without cognitive problems also have beta amyloid accumulation in their brains1 and beta amyloid can be present for years before symptoms of dementia can become apparent.2 We also don’t know what proportion of otherwise healthy people with beta amyloid in their brains will go on to develop Alzheimer’s disease.
How can we measure beta amyloid in the brain?
Research advances over the past decade have made it possible to detect beta amyloid in the brain through sophisticated neuroimaging techniques. In particular, special “tracers”, which bind to beta amyloid, are used with positron emission tomography (PET) to measure the amount of beta amyloid in a person’s brain.
Where is amyloid imaging available?
Amyloid imaging has not yet been approved for clinical use in Canada, although it is used in some Canadian research studies. The technology is available in the United States; in 2012, it was approved by the US Food and Drug Administration. In 2012, leading Canadian dementia experts also put forward recommendations on the use of amyloid imaging in the Canadian Consensus Conference on the Diagnosis and Treatment of Dementia (CCCDTD4).3 In CCCDTD4, the experts agreed that amyloid imaging is not ready for widespread use in Canada, and more research is needed to validate and evaluate this technology. In the meantime, they have specifically cautioned those who have obtained amyloid imaging outside Canada, recommending the results should only be interpreted with a specialist who is familiar with this technique.
When should amyloid imaging be used?
Amyloid imaging has great potential as a tool for diagnosing dementia (including differentiating types of dementia)4 and improving care, but there are still many unknowns. Although the regulatory status of amyloid imaging is different in Canada and the United States, experts on both side of the border have agreed that used alone, amyloid imaging cannot diagnose Alzheimer’s disease and other dementias.3,5 If the technology becomes available in Canada, amyloid imaging must only ever be used in conjunction with a thorough and detailed clinical exam and in consultation with specialists.3 Further, since we don’t know what proportion of people with positive amyloid scans will go on to develop Alzheimer’s disease, amyloid imaging should not be used for screening people without symptoms of dementia;3,5 in this case, the potential harms outweigh the benefits.
- Rowe CC, et al. Amyloid imaging results from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study of aging. Neurobiol Aging. 2010 Aug;31(8):1275-83.
- Villemagne VL et al. Longitudinal assessment of Aβ and cognition in aging and Alzheimer disease. Ann Neurol. 2011 Jan;69(1):181-92.
- Gauthier S, Patterson C, Chertkow H, Gordon M, Herrmann N, Rockwood K, Rosa-Neto P, Soucy JP. Recommendations of the 4th Canadian Consensus Conference on the Diagnosis and Treatment of Dementia (CCCDTD4). Can Geriatr J. 2012 Dec;15(4):120-6.
- Laforce R Jr, Rabinovici GD. Amyloid imaging in the differential diagnosis of dementia: review and potential clinical applications. Alzheimers Res Ther. 2011 Nov 10;3(6):31.
- Johnson KA, Minoshima S, Bohnen NI, Donohoe KJ, Foster NL, Herscovitch P, Karlawish JH, Rowe CC, Carrillo MC, Hartley DM, Hedrick S, Pappas V, Thies WH. Appropriate use criteria for amyloid PET: a report of the Amyloid Imaging Task Force, the Society of Nuclear Medicine and Molecular Imaging, and the Alzheimer's Association. Alzheimers Dement. 2013 Jan;9(1):e-1-16.