Oral Presentation Australian and New Zealand Society for Geriatric Medicine Annual Scientific Meeting 2025

Regional glucose hypometabolism demonstrated on FDG-PET imaging is dynamic in delirium superimposed on dementia (117197)

Aaron Johnson 1 , Anita Nitchingham 1 , Robert Welschinger 1 , Eva Wegner 1 , Christopher Rowe 2 , Vincent Dore 2 , Kun Huang 2 , Gideon Caplan 1
  1. Prince of Wales Hospital, Sydney
  2. Austin Health, Melbourne

Aims: Delirium superimposed on dementia (DSD) poses a significant diagnostic challenge in clinical practice and is associated with outcomes worse than delirium without dementia1,2. There is a need to develop strategies that more accurately differentiate between delirium, dementia, and DSD. The aims of this study were to describe the changes in cerebral glucose metabolism on fluorodeoxyglucose positron emission tomography (FDG-PET) in DSD and determine whether underlying neuropathology influences these changes. 

Methods: Cerebral glucose metabolism was examined using FDG-PET imaging in two groups: acutely unwell inpatients experiencing delirium with a background of Alzheimer's dementia (DSD group, N = 20) and well outpatients with Alzheimer's dementia alone (AD group, N = 19). Using semi-quantitative analysis, regional cerebral glucose metabolism in the DSD group was compared to the AD group to identify specific brain regions affected in DSD.

Results: There was predominant cortical cerebral glucose hypometabolism in the DSD group compared with the AD group. This involved the lateral frontal, parietotemporal, inferior posterior temporal and visual cortices bilaterally. In contrast, most subcortical regions demonstrated similar levels of glucose metabolism between the groups. 

Conclusions: Regional cerebral glucose metabolism in DSD does not represent an overlay of the changes that occur in delirium onto those that occur in AD3,4. This suggests that regional glucose hypometabolism in DSD may be influenced by other factors such as underlying neuropathology or acute illness. Neuropathology in AD predominantly affects the cortex of the brain, which may explain the cortical distribution of regional cerebral glucose hypometabolism in DSD. 

  1. Caplan GA. Delirium Superimposed Upon Dementia. J Am Med Dir Assoc. 2019;20(11):1382-3.
  2. Nitchingham A, Caplan GA. Current Challenges in the Recognition and Management of Delirium Superimposed on Dementia. Neuropsychiatr Dis Treat. 2021;17:1341-52.
  3. Nitchingham A, Pereira JV, Wegner EA, Oxenham V, Close J, Caplan GA. Regional cerebral hypometabolism on 18F-FDG PET/CT scan in delirium is independent of acute illness and dementia. Alzheimers Dement. 2023;19(1):97-106.
  4. Haggstrom LR, Nelson JA, Wegner EA, Caplan GA. 2-(18)F-fluoro-2-deoxyglucose positron emission tomography in delirium. J Cereb Blood Flow Metab. 2017;37(11):3556-67.