The atrophy pattern in Alzheimer-related PPA is more widespread than that of the frontotemporal lobar degeneration associated variants

Abstract

Objective: The three recognized variants of primary progressive aphasia (PPA) are associated with different loci of degeneration-left posterior perisylvian in logopenic variant (lvPPA), left frontal operculum in non-fluent variant (nfvPPA), and left rostroventral-temporal in semantic variant (svPPA). Meanwhile, it has become apparent that patients with lvPPA, in which Alzheimer pathology is the norm, frequently have more extensive language deficits-namely semantic and grammatical problems-than is captured in the strict diagnostic recommendations for this variant. We hypothesized that this may be because the degeneration in AD-related PPA typically extends beyond the left posterior perisylvian region.

Methods: Magnetic resonance images from 25 PPA patients (9AD-related PPA, 10 svPPA, 6 nfvPPA) and a healthy control cohort were used to calculate cortical thickness in three regions of interest (ROIs). The three ROIs being the left-hemispheric loci of maximal reported degeneration for each of the three variants of PPA.

Results: Consistent with past studies, the most severe cortical thinning was in the posterior perisylvian ROI in AD-related PPA; the ventral temporal ROI in svPPA; and the frontal opercular ROI in nfvPPA. Significant cortical thinning in AD-related PPA, however, was evident in all three ROIs. In contrast, thinning in svPPA and nfvPPA was largely restricted to their known peak loci of degeneration.

Conclusions: Although cortical degeneration in AD-related PPA is maximal in the left posterior perisylvian region, it extends more diffusely throughout the left hemisphere language network offering a plausible explanation for why the linguistic profile of lvPPA so often includes additional semantic and grammatic deficits.

Keywords: AD-related PPA; Alzheimer pathology; Atrophy; PPA.

Fig. 1

Whole-brain cortical thinning displayed on the pial surface for every PPA variant compared to a cohort of healthy age-matched volunteers. FDR-corrected (p < .001).

Fig. 2

Whole-brain cortical thinning of the three PPA groups; this is the same analysis and statistical threshold as presented in Fig. 1, except that the default FreeSurfer 10 mm smoothing kernel was employed.

Fig. 3

Results from the ROI analysis for the ROIs a) IFG b) PPS c) AFA; boxplot = 1st, 2nd, 3rd quartile; whiskers 95% CI; * = p < .05; ** = p < .005; *** = p < .001.