Amyloid deposition in semantic dementia: a positron emission tomography study

Background: Pittsburgh 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.

Objective: Comparison 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.

Methods: Subjects 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.

Results: The 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.

Conclusions: Aβ 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.