Metabolic alterations associated with impaired clock drawing in Lewy body dementia

The clock drawing test (CDT) is a widely used dementia screening instrument that assesses executive and visuospatial abilities; studies in patients with Alzheimer's disease (AD) suggest frontoposterior networks to be involved in clock drawing. Clock drawing errors are also often observed in dementia with Lewy bodies (DLB), but the functional neuroanatomical substrate of impaired clock drawing has not been firmly established in this disorder. The present study was designed to provide initial evidence for brain metabolic alterations associated with CDT performance in DLB. Twenty-one patients with DLB were enrolled. CDT ratings were correlated with the regional cerebral metabolic rate of glucose (rCMRglc) measured by 18F-fluoro-2-deoxy-glucose positron emission tomography (18F-FDG PET) in the statistical parametric mapping software package SPM5, controlling for overall cognitive impairment as measured by the Mini-Mental-State Examination (MMSE) score. There was a significant negative association between test scores and rCMRglc in a left-hemispheric posterofrontal network including the temporoparietal and dorsal pre-motor cortices and the precuneus. The present study provides evidence for a direct association between frontoparietal dysfunction and impaired CDT performance in DLB. These findings also suggest that the CDT is an appropriate screening instrument for this disorder and that metabolic dysfunction, and therefore disease severity, is mirrored by performance on the test.