Transcranial Doppler to measure cerebral blood flow in delirium superimposed on dementia. A cohort study.

OBJECTIVE

Delirium superimposed on dementia (DSD) is frequently not diagnosed, at great cost. Both delirium and dementia are associated with cerebral hypoperfusion. A switch to anaerobic glycolysis in the central nervous system during delirium compared to Alzheimer's dementia (AD) suggests greater hypoperfusion in DSD. The main aims of this study were to investigate whether cerebral hypoperfusion could differentiate DSD from related entities, and the characteristics of that hypoperfusion.

METHODS

Prospective cohort study of 44 Geriatric Medicine patients in 4 groups: (1) delirium, no history of dementia; (2) DSD; (3) acute illness without delirium or dementia; and (4) AD, no delirium. We measured CBF using transcranial Doppler to assess flow velocity (FV) and pulsatility index in the middle cerebral artery (MCA).

RESULTS

DSD has lower FV than either AD or delirium alone, or acute illness (28.2 ± 4.7 vs AD: 41.3 ±15.7; P = .040; vs delirium 37.7 ± 8.2; P =.009; vs acute illness 43.0 ± 8.3; P <.001). A mean MCA FV cut-off of 32.25 cm/s diagnoses DSD with a sensitivity of 0.875 and specificity of 0.788, area under the curve 0.884; P = .001. Resolution of delirium improves FV (P = .005). FV correlates with delirium severity (delirium index R = -0.39; P = .009) and dementia (Mini-Mental State Examination, R = 0.33; P = .029, and Informant Questionnaire on Cognitive Decline in the Elderly, R = -0.41; P = .005).

CONCLUSIONS

Transcranial Doppler is a potential diagnostic and monitoring test for DSD. Correlation with clinical indicators of delirium suggests pathophysiological significance.