Acoustic and Kinematic Assessment of Motor Speech Impairment in Patients With Suspected Four-Repeat Tauopathies

Abstract

Purpose: The aim of this study was to use acoustic and kinematic speech measures to characterize type of motor speech impairment-apraxia of speech (AOS) versus dysarthria-in individuals with four-repeat tauopathy (4RT)-associated syndromes, including nonfluent variant primary progressive aphasia (nfvPPA), primary progressive AOS (PPAOS), corticobasal syndrome (CBS), and progressive supranuclear palsy syndrome (PSPs).

Method: Twenty patient participants were recruited and stratified into two groups: (a) a motor-speech-impaired group of individuals with nfvPPA, PPAOS, CBS, or PSPs and suspected 4RT pathology ("MSI+") and (b) a non-motor-speech-impaired group of individuals with logopenic variant primary progressive aphasia ("MSI-"). Ten healthy, age-matched controls also participated in the study. Participants completed a battery of speech tasks, and 15 acoustic and kinematic speech measures were derived. Quantitative speech measures were grouped into feature categories ("AOS features," "dysarthria features," "shared features"). In addition to quantitative speech measures, two certified speech-language pathologists made independent, blinded auditory-perceptual ratings of motor speech impairment. A principal component analysis (PCA) was conducted to investigate the relative contributions of quantitative features.

Results: Quantitative speech measures were generally concordant with independent clinician ratings of motor speech impairment severity. Hypothesis-driven groupings of quantitative measures differentiated predominantly apraxic from predominantly dysarthric presentations within the MSI+ group. PCA results provided additional evidence for differential profiles of motor speech impairment in the MSI+ group; heterogeneity across individuals is explained in large part by varying levels of overall severity-captured by the shared feature variable group-and degree of apraxia severity, as measured by the AOS feature variable group.

Conclusions: Quantitative features reveal heterogeneity of MSI in the 4RT group in terms of both overall severity and subtype of MSI. Results suggest the potential for acoustic and kinematic speech assessment methods to inform characterization of motor speech impairment in 4RT-associated syndromes.

Supplemental material: https://doi.org/10.23641/asha.21401778.

Figure 1.

Flowchart detailing the process by which study participants were recruited, grouped, and assessed in the current study, as well as study-specific measures that form the basis of study results. CBS = corticobasal syndrome; CVC = consonant–vowel–consonant; DDK = diadochokinesis; HC = healthy controls; lvPPA = logopenic variant primary progressive aphasia; nfvPPA = nonfluent variant primary progressive aphasia; PPA = primary progressive aphasia; PPAOS = primary progressive apraxia of speech; PSPs = progressive supranuclear palsy syndrome; SIT = Speech Intelligibility Test; SLP = speech-language pathologist; WAB-R = Western Aphasia Battery–Revised. ^aInitial syndrome diagnoses (e.g., PPAOS, nfvPPA) and subgroupings (MSI+, MSI−) are treated as the diagnostic ground truth in the current study and are maintained even in cases where subsequent study-specific analyses—either quantitative speech measures and/or blinded auditory-perceptual ratings—did not agree with these initial designations.

Figure 2.

Classification and grouping schema for quantitative speech measures. (A) Listing of all quantitative speech measures, including abbreviation and category assignment. (B) Graphical representation of feature category assignment, indicating “AOS features” (left), “shared features” (overlap), and “dysarthria features” (right). AMR = alternating motion rate; AOS = apraxia of speech; SMR = sequential motion rate.

Figure 3.

Quantitative profiles of motor speech impairment across each of the three feature categories for the MSI+ group as compared with the MSI− group. Red shaded area at |z| ≥ 2 indicates cutoff for atypical (relative to healthy control mean) values. AOS = apraxia of speech; Dys = dysarthria.

Figure 4.

Principal component analysis results show stratification of MSI+ patients and reflect within-group heterogeneity in severity and speech features. Gray arrows indicate individual loadings for each quantitative variable. Group membership was connoted by shape and outline color, fill shaded based on Sentence Intelligibility Test (SIT) scores (%). For the MSI+ group only, individual patients are indicated with case numbers for cross-referencing purposes. PC1 = Component 1 (% variance explained); PC2 = Component 2 (% variance explained).

Figure 5.

Individual speech measures load differentially on Components 1 and 2, reflecting “Overall Severity” (C1) and “AOS Severity” (C2). Reference dashed red line indicates expected value (%) if all variable contributions were uniform. PC1 = Component 1; PC2 = Component 2; AMR = alternating motion rate; SMR = sequential motion rate.