Quantitative assessment of motor speech impairment in primary progressive aphasia
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CitationCordella, Claire. 2019. Quantitative assessment of motor speech impairment in primary progressive aphasia. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractPrimary progressive aphasia is a neurodegenerative aphasic syndrome that can be classified into three main variants: agrammatic/non-fluent (nfvPPA), logopenic (lvPPA), and semantic (svPPA). Motor speech impairment is a key diagnostic marker used to aid classification of the clinical variants of PPA. Identification of motor speech symptoms is useful not only for differential diagnosis of PPA subtypes but may also inform hypotheses related to anatomic localization of disease and underlying pathophysiologic mechanisms. However, the diagnosis and characterization of motor speech impairment poses unique challenges when applied to the PPA population. First, motor speech impairment must be differentiated from comorbid language impairment and second—upon identification of a motor speech impairment—a disorder of motor planning (i.e., apraxia of speech) must be differentiated from one of motor execution (i.e., dysarthria).
The proposed series of acoustic, kinematic, and imaging-based analyses were designed to assess the diagnostic efficacy and biological validity of quantitative speech measures for identifying motor speech impairment in PPA, and to determine if motor speech impairments in PPA are consistent with apraxia of speech and/or dysarthria. In Study 1, we investigate the diagnostic accuracy of quantitative measures of speech rate as compared to clinician-rated measures to identify nfvPPA (cf. lvPPA, svPPA). Study 1 results provide evidence that an articulation rate (AR) measure may be a useful quantitative proxy of motor speech impairment. Study 2 extends this finding and evaluates whether the AR measure sensitively detects very mild motor speech impairment in PPA, and whether the AR measure is responsive to longitudinal changes in motor speech function. We also investigate the neuroanatomical basis of motor speech impairment in PPA by relating the AR measure to cortical thickness in motor speech regions of interest. Lastly, in Study 3, we go beyond mere identification of motor speech impairment and seek to characterize individual profiles of motor speech impairment—with specific reference to apraxic and dysarthric features—using acoustic and kinematic measures of motor speech function. Results of the study series are interpreted in light of potential contributions to (1) diagnostic subtyping, (2) clinical monitoring, and (3) development of speech motor outcome measures.
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