Subtypes of progressive aphasia: application of the international consensus criteria and validation using β-amyloid imaging

Abstract

Primary progressive aphasia comprises a heterogeneous group of neurodegenerative conditions with diverse clinical profiles and underlying pathological substrates. A major development has been the publication of the recent International Consensus Criteria for the three major variants namely: semantic, non-fluent/agrammatic and logopenic. The logopenic variant is assumed to represent an atypical presentation of Alzheimer pathology although evidence for this is, at present, limited. The semantic and non-fluent/agrammatic variants are largely associated with frontotemporal lobar degeneration with TDP-43 and tau pathology, respectively. The applicability of the International Consensus Criteria to an unselected clinical sample is unknown and no agreed clinical evaluation scale on which to derive the diagnosis exists. We assessed 47 consecutive cases of primary progressive aphasic seen over a 3-year period in a specialist centre, using a newly developed progressive aphasia language scale. A subgroup of 30 cases underwent (11)C-labelled Pittsburgh Compound B positron emission tomography imaging, a putative biomarker of Alzheimer's disease that detects β-amyloid accumulation, and they were compared with an age-matched group (n = 10) with typical, predominately amnestic Alzheimer's disease. The application of an algorithm based on four key speech and language variables (motor speech disorders, agrammatism, single-word comprehension and sentence repetition) classified 45 of 47 (96%) of patients and showed high concordance with the gold standard expert clinical diagnosis based on the International Consensus Criteria. The level of neocortical β-amyloid burden varied considerably across aphasic variants. Of 13 logopenic patients, 12 (92%) had positive β-amyloid uptake. In contrast, one of nine (11%) semantic variant and two of eight (25%) non-fluent/agrammatic cases were positive. The distribution of β-amyloid across cortical regions of interest was identical in cases with the logopenic variant to that of patients with typical Alzheimer's disease although the total load was lower in the aphasic cases. Impairments of sentence repetition and sentence comprehension were positively correlated with neocortical burden of β-amyloid, whereas impaired single-word comprehension showed a negative correlation. The International Consensus Criteria can be applied to the majority of cases with primary progressive aphasic using a simple speech and language assessment scale based upon four key variables. β-amyloid imaging confirms the higher rate of Alzheimer pathology in the logopenic variant and, in turn, the low rates in the other two variants. The study offers insight into the biological basis of clinical manifestations of Alzheimer's disease, which appear topographically independent of β-amyloid load.

Can MRI Visual Assessment Differentiate the Variants of Primary-Progressive Aphasia?

“…18 Furthermore, some researchers have proposed to diagnose lvPPA through a hierarchic decision tree in which the key feature of this group is that they are neither svPPA nor nfvPPA. 19 Applying such an algorithm to the present mixed cases would also have them classified as lvPPA. The subjects with mixed PPA in this study should, therefore, be considered analogous to those with lvPPA and are referred to henceforth as such.…”

“…While a number of studies have failed to demonstrate the utility of these features in the diagnosis of lvPPA, 17,45 atrophy of the left temporoparietal lobe has been consistently emphasized in Alzheimer disease-related aphasia. 17,19,45 In the "Materials and Methods" section, we mentioned our rationale for applying the lvPPA label to the group of patients with PPA whom we had previously reported as having mixed PPA. Turning to the individual visual reporting outcomes, we found low-to-moderate sensitivity (mean, 49% Ϯ 7%) for the prescribed atrophy patterns.…”

“…This radiologic finding resonates with the previously reported difficulty in distinguishing nfv-and lvPPA variants on clinical and neuropsychological grounds. 19,45 None of the radiologists had reported global atrophy for the n ϭ 16 lvPPA cohort. This is an important negative, given possible concerns about the severity of dementia in this group.…”

C9ORF72 repeat expansion in clinical and neuropathologic frontotemporal dementia cohorts

“…16 Our progressive aphasia group (n ϭ 39) included 8 with the newly recognized logopenic variant, which has been associated with underlying Alzheimer pathology. 17 They were included because clinical differentiation from the other variants of progressive aphasia requires relatively sophisticated analysis of speech and in most centers such cases would be subsumed under the broad rubric of FTD.…”

Spoken discourse in Alzheimer' disease: a review

“…Imaging studies have identified damage typically in the left temporoparietal junction, and a recent study showed that the severity of imaging abnormalities in this region correlated with the performance on naming and sentence repetition (Leyton et al 2012). Less consistent damage has been noted in the medial temporal and parietal cortex, posterior cingulate, inferior frontal and temporo-parietal cortex (GornoTempini et al 2008;Gorno-Tempini et al 2004;Rohrer et al 2010).…”