Lexical Markers of Disordered Speech in Primary Progressive Aphasia and ‘Parkinson-plus’ Disorders

Abstract

AbstractConnected speech samples elicited by a picture description task are widely used in the assessment of aphasias, but it is not clear what their interpretation should focus on. Although such samples are easy to collect, analyses of them tend to be time-consuming, inconsistently conducted, and impractical for non-specialist settings. Here, we analysed connected speech samples from patients with the three variants of primary progressive aphasia (svPPA N = 9, lvPPA N = 9, nfvPPA N = 9), progressive supranuclear palsy (PSP Richardson’s syndrome N = 10), corticobasal syndrome (CBS N = 13), and age-matched healthy controls. There were three principal aims. First, to determine the differences in quantitative language output and psycholinguistic properties of words produced by patients and controls. Second, to identify the neural correlates of connected speech measures. Third, to develop a simple clinical measurement tool: using data-driven methods, we optimised a 15-word checklist for use with the Boston Diagnostic Aphasia Examination ‘cookie theft’ and Mini Linguistic Aphasia Examination ‘beach scene’ pictures and tested the predictive validity of outputs fromLeast Absolute Shrinkage and Selection Operator(LASSO) models using an independent clinical sample from a second site. The total language output was significantly reduced in patients with nfvPPA, PSP and CBS relative to those with svPPA and controls. Patients with lvPPA and svPPA were found to use a disproportionately greater use of words that were more frequent and semantically diverse. Results from voxel-based morphometry analyses across the whole group revealed correlations between grey matter volume in (i) bilateral frontal lobes with overall language output, (ii) the left frontal and superior temporal regions with speech complexity, (iii) bilateral frontotemporal regions with phonology, and (iv) bilateral cingulate and subcortical regions with age of acquisition. With the 15-word checklists, the LASSO models showed excellent accuracy for within-samplek-fold classification (over 95%) and out-of-sample validation between patients and controls (over 90%), and moderately good (59% - 70%) differentiation between the motor disorders (nfvPPA, PSP, CBS) and lexico-semantic groups (svPPA, lvPPA). In conclusion, we propose that a simple 15-word checklist provides a suitable screening test to identify people with progressive aphasia, while further specialist assessment is likely to be needed to differentiate accurately some groups (e.g., svPPA versus lvPPA and PSP versus CBS).