Neuropsychological function and cerebral glucose utilization in isolated memory impairment and Alzheimer's disease

We hypothesized that 20 patients with isolated memory impairment (IMI) woul d demonstrate [F-18]-2-fluoro-2-deoxy-D-glucose utilization and a progressi on of neuropsychological symptoms consistent with Alzheimer's disease (AD). IMI subjects performed similarly to AD in recall and verbal fluency, but c omparable to normal subjects in other areas of cognitive functioning. A pos itron emission tomography (PET) diagnostic index based on parietal Z-scores categorized IMI patients into normal and abnormal metabolic patterns. Ten of the original 20 IMI patients (50%) reflected PET AD abnormalities. Clinical information was available for IMI patients at three-year follow-up . Ten (50%) had converted to AD, three were found to have pseudodementia an d the seven remained IMI. Of the 10 IMI patients with an originally normal PET index, three (30%) were diagnosed with AD at three years. Of the 10 wit h an abnormal index originally, seven (70%) converted to AD. The finding that memory deficit in IMI was as pronounced as that in AD pati ents is consistent with the notion that memory is an initial symptom of AD. A substantial number of the IMI patients reflected regional hypometabolism similar to AD, suggesting that IMI is likely an early stage in progressive dementia. A large percentage of IMI patients converted clinically to AD wi thin three years of initial study, though we observed impaired memory funct ioning well before a clinical diagnosis of AD could be made. In addition to potential clinical utility, IMI and PET represent an opportunity to study dementia in relation to brain chemistry at a time when brain pathology is i n the process of development. (C) 1999 Elsevier Science Ltd. All rights res erved.