Impaired memory and executive function associated with decreased medial temporal and prefrontal blood flow in Clinical Dementia Rating 0.5 status: the Osaki‐Tajiri project

Aim: The Clinical Dementia Rating (CDR) is an assessment of dementia severity based on observations of activities of daily living, and a CDR of 0.5 (CDR 0.5) represents questionable dementia. A combination of the Cognitive Abilities Screening Instrument (CASI) and the Trail Making Test (TMT) scores discriminated CDR 0.5 subjects from healthy participants with a high degree of accuracy. We investigated the neurological background of CDR 0.5 subjects by correlating CASI and TMT scores with regional cerebral blood flow (rCBF) as measured by single photon emission computed tomography (SPECT). Methods: From a community‐based cohort, 22 CDR 0.5 participants were recruited. CASI and TMT scores, rCBF measure using [¹²³I]‐N‐isopropyl‐p‐iodoamphetamine and SPECT were obtained. We evaluated the relationships between the CASI domain scores, between TMT scores and rCBF in a regions‐of‐interest‐based analysis, and voxel‐based analysis using Statistical Parametric Mapping 5 software. Results: We found that lower rCBF in the left medial temporal cortex correlated with a decreased CASI domain recent memory score both in the regions‐of‐interest and statistical parametric mapping analysis. In both the regions‐of‐interest and statistical parametric mapping analysis, the rCBF in the left prefrontal cortex correlated with CASI domain remote memory and mental manipulation and concentration. Conclusions: Our results indicate that some CDR 0.5 subjects have functional impairments in the medial temporal lobe as well as in the prefrontal cortex, as reflected in the cognitive decline measured by CASI and TMT.