PET-CT, the likelihood of progression to dementia is low. This can provide useful reassurance and prevent the use of costly and unnecessary treatment11
.
Brain amyloid PET-CT imaging As an alternative strategy to imaging regional cerebral glucose metabolism in patients with suspected dementia, tracers have been developed to specifically bind the abnormal -amyloid (A) deposition characteristic of this condition. Currently in the UK, only one radiopharmaceutical is commercially available for amyloid PET-CT imaging – 18F-florbetapir (Amyvid™, Lilly, Indianapolis, IN, USA). Even so, there is evidence in the literature of similar compounds that have proven successful in differentiating between normal volunteers and subjects with Alzheimer’s disease, dementia with Lewy bodies, fronto-temporal dementia and mild cognitive impairment (MCI). The level of uptake in amyloid PET-CT scans is significantly higher in patients with Alzheimer’s disease and the pattern of uptake is similar to the regional hypometabolism in 18
F-FDG PET-CT scans17 .
Amyloid uptake has also been shown to be higher in subjects with dementia with Lewy bodies than in healthy controls and those with Parkinson’s disease or Parkinson’s disease with dementia. There is overlap in appearances such that amyloid imaging may not be helpful in differentiating these two dementia types16
. Since A deposition is not a feature of fronto-temporal dementia, these patients show scan
appearances similar to age-matched healthy subjects; amyloid PET-CT imaging should have a role in differentiating fronto-temporal dementia from Alzheimer’s disease16
.
Finally, patients with MCI that are found to have normal, age-matched uptake on amyloid PET-CT imaging are unlikely to progress to dementia17
. Therefore, using this test in MCI patients to differentiate
those with normal scan appearances from those with scan features suggestive of Alzheimer’s disease, would potentially permit appropriate withholding of expensive treatment from the former group, whilst simultaneously allowing early treatment intervention in the latter, should such treatment become available.
F-FDG and amyloid PET-CT imaging studies have been shown to add benefit over clinical assessment alone in the diagnosis of dementia. Anatomical imaging provides greater ease of access and also rules out structural reasons for dementia-like symptoms. With prominent political figures supporting the drive to better manage dementia, where is the message being lost in gaining the funding from commissioners to support the development of diagnostic tools to enable early dementia diagnosis? A drive to research the use of these imaging techniques in dementia could provide the evidence base to support appropriate commissioning.
Conclusion 18
Acknowledgements Bernadette Cronin and Daniel Levine are thanked for their advice and for reviewing this article.
-29-
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ABOUT THE AUTHOR David Fitzgerald is Radioisotope Service Manager in the Department of Nuclear Medicine and PET- CT, Royal Marsden NHS Foundation Trust. His interests include leadership and role development for nuclear medicine technologists/radiographers. He is a member of the SoR Nuclear Medicine Advisory Group and sits on the London – Surrey Borders Research Ethics Committee.
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