BACKGROUND: Semantic dementia (SD) is a type of primary progressive aphasia with prominent language dysfunction, mostly within the spectrum of frontotemporal lobar degeneration (FTLD). Although there is an overlap in clinical manifestations of SD attributable to FTLD and neuropathologically proven Alzheimer disease (AD), clinical diagnostic clues are not readily available. We present a characteristic finding based on a single-photon emission computed tomography (SPECT)-based regional cerebral blood flow study and its statistical imaging analysis for a rare case of SD with AD-like pathology.

CASE REPORT: A 61-year-old male was referred to our hospital due to difficulties in self-management and impaired comprehension of word meaning suggestive of SD. Although his brain MRI revealed mild frontal lobe atrophy, his SPECT with three-dimensional stereotactic surface projections (3D-SSP) analysis showed left-sided hypo-perfusion that was more prominent in the inferior temporal gyrus and the inferior parietal lobule, with bilateral frontal lobe hypo-perfusion. The SPECT scan also showed involvement of the right inferior parietal area and, in medial aspects, the posterior cingulate cortex and adjacent precuneus; these finding were compatible with early hypo-perfused areas seen in AD. The lumbar cerebrospinal fluid biomarker findings seemed to fit SD in association with probable AD pathology.

CONCLUSIONS: This is the first reported case to use SPECT with 3D-SSP statistical analysis as a potential, useful imaging modality for the diagnosis of SD with probable AD pathology.

Keywords: Alzheimer Disease, Aphasia, Primary Progressive, Biological Markers, Cerebrospinal Fluid, frontotemporal dementia, Tomography, Emission-Computed, Single-Photon