Amyloid deposition in semantic dementia: a positron emission tomography study

Abstract

BackgroundPittsburgh compound B ([11C]‐PIB) identifies amyloid‐β (Aβ) deposition in vivo. Asymptomatic Aβ deposition has been reported consistently in some healthy older subjects. Of patients with frontotemporal dementia, those who have later onset have a higher potential for Aβ deposition.ObjectiveComparison of Aβ deposition in Alzheimer's disease (AD), healthy older controls, and patients with early‐ and late‐onset semantic dementia (SD), a subtype of frontotemporal dementia.MethodsSubjects were recruited from tertiary academic care centers specializing in assessment and management of patients with neurodegenerative disease. We used the radiotracer [11C]‐PIB in a high‐resolution positron emission tomography scanner to evaluate 11 participants with SD (six with onset before age 65 and five with later onset), 9 with probable AD, and 10 controls over age 60. The main outcome measures were frontal, temporal, parietal, and total [11C]‐PIB standardized uptake value ratios to establish PIB‐positive (PIB+) cutoff.ResultsThe five patients with late‐onset SD were PIB‐negative. Two of six with early‐onset SD, seven of nine with AD, and 1 of 10 controls were PIB+. The SD participants who were PIB+ did not have memory or visuospatial deficits that are typical in AD.ConclusionsAβ deposition does not seem to be associated with late‐onset SD. Future larger studies might confirm whether a significant minority of early‐onset SD patients exhibit Aβ deposition. Copyright © 2016 John Wiley & Sons, Ltd.

Parietal Involvement in the Semantic Variant of Primary Progressive Aphasia with Alzheimer’s Disease Cerebrospinal Fluid Profile

“…However, svPPA patients with biological profile of AD are very rare. The percentage of svPPA-AD in our series (14%) is absolutely in line with previous studies revealing AD pathology in svPPA [6][7][8][9][10][13][14][15]19,[24][25][26][27][28][29] (Table 1). Moreover, we acknowledge that it would be preferable to have FDG-PET data for a better spatial resolution and sensitivity.…”

“…This second hypothesis would imply that late-onset svPPA might be more frequently associated with amyloid pathology than early-onset svPPA. A recent amyloid PET study in svPPA does not corroborate this hypothesis [24]. Moreover, two of our svPPA-AD patients have a disease onset before the age of 60 years, which cannot be considered as late-onset.…”

“…Pathologically, svPPA is nearly always associated with underlying TAR DNA-binding protein 43 (TDP-43) aggregates [14,15,23]. However, in a small proportion of cases, in vivo studies such as cerebrospinal fluid (CSF) analyses and amyloid imaging [19,[24][25][26][27] and also post mortem series [7][8][9][10][11][12][13][14][15]28,29] have reported Alzheimer's disease (AD) as pathological substrate (Table 1).…”

“…In this context, the biological surrogates for underlying AD pathology, including amyloid positron emission tomography (PET) and measurements of total tau, phosphorylated tau at threonine 181 (P-tau) and amyloid-β peptide 1-42 (Aβ42) in the CSF, are relevant to define the causative pathology in complex clinical syndromes [24].…”

FTD spectrum: Neuroimaging across the FTD spectrum

“…Recent molecular PET imaging studies have produced some interesting findings in SD. Firstly, amyloid PET studies have shown that a high proportion, in fact up to 30%, of SD patients can have beta-amyloid deposition in their brains [159][160][161][162][163] . The presence of betaamyloid deposition does not appear to influence the clinical presentation of SD, although the patients with beta-amyloid tend to be older 163 .…”