Neuropsychological and Neuroimaging Findings of Frontal Variant of Alzheimer's Disease

ABSTRACT

BACKGROUND: Patients with Alzheimer's disease (AD) at an early stage present with memory decline and impairments of language and visuospatial functions. However, some AD patients occasionally show frontal lobe dysfunctions in the early stage those are known to emerge only at the advanced stage. This subtype of AD is called a frontal variant of AD (frontal AD). We report neuropsychological and FDG-PET findings of three cases of frontal AD. METHODS: Three patients met the diagnostic criteria of probable AD proposed by the NINCDS-ADRDA. However, they unusually showed clinical symptoms associated with frontal lobe dysfunctions even if they were relatively in the early stage of dementia. All the patients underwent neuropsychological tests and brain FDG-PET scans. Distribution of glucose hypometabolism was analyzed using statistical parametric mappings (SPM). RESULTS: Results of neuropsychological tests were consistent with findings of AD except that frontal lobe dysfunctions were prominent. FDG-PET scans and SPM analysis of these images showed hypometabolism in the frontal as well as temporo-parietal regions. Unlike the hypometabolism pattern found in frontotemporal dementia, frontal hypometabolism in our patients was not as severe as parietal hypometablism and hypometabolic regions within the temporal lobe were in the middle or posterior part of the middle and inferior temporal gyri rather than in the anterior part. CONCLUSIONS: Detailed neuropsycholgical tests and FDG-PET may help differentiate AD with frontal involvement in its early stage (frontal AD) from frontotemporal dementia. Future studies with FDG-PET in a larger series of frontal AD cases, especially with histologically proven cases, may be needed.