Dementia in Down's syndrome: cerebral glucose utilization, neuropsychological assessment, and neuropathology.

We measured the cerebral metabolic rate for glucose (CMRglc) with positron emission tomography and [18F]2-fluoro-2-deoxy-D-glucose in a 47-year-old man with trisomy 21 Down's syndrome (DS) and autopsy-confirmed Alzheimer's disease. Dementia was evident from a confirmed history of cognitive decline, memory loss, and personality change. CMRglc in the subject was compared with the mean obtained in 13 healthy younger DS subjects, aged 19 to 33 years. Test scores of general intelligence, visuospatial ability, language, and memory function showed poorer performance in the older subject compared with the younger group. Mean hemispheric CMRglc in the older DS subject was 28% less than in the young DS group, and marked hypometabolism was evident in parietal and temporal lobe association cortices. At autopsy, extensive neuropathology was noted, especially in the parietal and temporal cortical regions, more so than reported in DS subjects without documented dementia. This study is the first complete assessment of cerebral metabolism, neuropsychological competence, and neuropathology in a DS subject with a documented course of dementia, and demonstrates the superimposition of Alzheimer type dementia on previous mental retardation.