Clock Drawing Test in Mild Cognitive Impairment: Correlation With Cerebral Perfusion in Single-Photon Emission Computed Tomography

Objective: This study aimed to understand the relationship between the Clock Drawing Test (CDT) and decreased blood flow in mild cognitive impairment (MCI) patients, using single-photon emission computed tomography. Method: We characterized regional cerebral blood flow (rCBF) and the correlation with clinical variables and future conversion to dementia in 94 amnestic MCI patients. Blood perfusion data was correlated with the CDT (quantitative and qualitative scores) in order to evaluate their relationship and usefulness in predicting conversion to dementia. Results: MCI patients displayed reduced rCBF in brain areas including the caudate nucleus; the frontal, parietal, and temporal lobes; as well as the cerebral cortex and cerebellum. The decrease in rCBF was higher for patients who later developed dementia. At baseline, CDT scores of these patients correlated with hypoperfusion in cortical and subcortical areas typically affected in Alzheimer's disease (AD) median 3 years before developing dementia. CDT total score was significantly correlated with rCBF in the left temporal lobe and the putamen; the analysis of rCBF in Brodmann areas showed significant correlations between the several clock elements (face, numbers, and hands), underlying qualitative errors (stimulus-bound response and conceptual deficit), and rCBF, most significantly in the left inferior temporal gyrus, posterior entorhinal cortex, posterior cingulate cortex, left parahippocampal cortex, and left inferior prefrontal gyrus. Conclusions: This study showed that a quantitative score and a qualitative assessment of clock drawing (error analysis) corresponded to dysfunction in AD key areas at an early stage, supporting the CDT utility in the detection of prodromal AD. General Scientific Summary The Clock Drawing Test is a popular instrument for the detection of Alzheimer's disease. With this study, we were able to confirm that a low score and errors in clock drawings correspond to decreased cerebral blood flow in key areas of Alzheimer's disease in its prodromal phase (known as mild cognitive impairment), median 3 years before the development of a dementia state.