Brain metabolism during delirium

Background

Altered cerebral glucose metabolism manifested by increased cerebrospinal fluid (CSF) lactate and decreased neuron specific enolase during delirium has been found in CSF analyses in multiple settings, although without change in CSF or blood glucose. These changes correlate with markers of delirium severity and outcomes of delirium.

However, patients with delirium are acutely unwell in hospital and have multiple comorbidities. The contribution of acute illness and dementia have not been excluded.

Method

We studied two groups of acutely unwell older people in hospital after excluding underlying dementia by history and the Informant Questionnaire on Cognitive Decline in the Elderly. The first group had delirium and the second group had no delirium. All patients underwent a ¹⁸F‐fluorodeoxyglucose positron emission tomography (FDG‐PET) scan in hospital while unwell, and during delirium for the first group. Confounders on FDG‐PET such as structural brain lesions and medications that affect brain metabolism were excluded.

Then we also compared the delirium FDG‐PET scans to a group with Alzheimer’s dementia.

Result

Patients with delirium demonstrated a unique, novel pattern of brain hypometabolism that reflected symptoms of delirium. The affected areas included: bilateral thalami; right posterior cingulate cortex (PCC); right superior frontal, right infero‐lateral anterior temporal and left superior parietal cortices. The areas highly negatively correlated with delirium severity scores (Spearman’s rank correlation coefficients between ρ = ‐0.39 and ‐0.71; p values from 0.089 to 0.001) and performance on a range of relevant neuropsychological tests, for example thalami and Trail Making Test B (Spearman’s ρ = ‐0.52; p = 0.028). Direct comparison to AD scans significant thalamic hypometabolism (p<0.01) in delirium, but the PCC was not different.

Conclusion

In patients with acute illness but without dementia, delirium is accompanied by regional cerebral hypometabolism in a distribution that is not consistent with any known pattern of dementia. While there is some overlap with AD, thalamic hypometabolism is atypical of AD and consistent with the clinical features of delirium.

References

Nitchingham AR, Pereira JV‐B, 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 & Dementia 2022; 1‐10.