Objective: This study examined the association of regional atrophy on MRI and motor speech in PSP.

Background: Motor speech impairment is common in PSP[1]. Although progressive apraxia of speech (PAOS) is a hallmark feature of the speech and language variant of PSP (PSP-SL), it is less common in other variants[1]. Atrophy of the SMA and premotor areas and abnormalities in SMA commissural fibers and motor tracts are associated with PAOS [2, 3]. The Apraxia of Speech Rating Scale (ASRS)[4] characterizes presence and severity of features of AOS, some of which overlap with dysarthria.  This study explored the relationship between ASRS and brain atrophy in PSP variants other than PSP-SL.

Method: 116 PSP participants (7 with PAOS, 102 with dysarthria), underwent volumetric MRI. ASRS scores ranged 0-52 (lower scores indicate fewer/less severe features of AOS). The clinical judgement of dysarthria severity ranged 0 (no dysarthria) to 4 (most severe). The regression model examined ASRS with explanatory variables of age, sex, PSPRS, dysarthria severity, and regional brain atrophy.

Results: Median score ASRS was 4 with interquartile range (IQR) 0-23. Median dysarthria severity was 2 with IQR 0-4. ASRS was related to PSP and dysarthria severity [figure1] but not age or sex. ASRS was associated with atrophy in SMA and superior frontal regions, and to a lesser extent the precentral region, but not the striatum, midbrain, or dentate nucleus, after accounting for dysarthria severity [figure2].

Conclusion: Although ASRS correlated with dysarthria severity (r = 0.56, p < 0.001), brain atrophy related to ASRS included cortical regions associated with PAOS (SMA and premotor) but not subcortical regions associated with dysarthria. The ASRS is sensitive to motor planning/programming impairments, even in the setting of concomitant dysarthria.

References: 1. Clark, H.M., et al., Motor Speech Disorders and Communication Limitations in Progressive Supranuclear Palsy. AJSLP, 2021: p. 1-12.
2. Whitwell, J.L., et al., Distinct regional anatomic and functional correlates of neurodegenerative apraxia of speech and aphasia: an MRI and FDG-PET study. Brain and Language, 2013. 125(3): p. 245-52.
3. Botha, H., et al., Disrupted functional connectivity in primary progressive apraxia of speech. NeuroImage: Clinical, 2018. 18: p. 617-629.
4. Duffy, J.R., et al., The Apraxia of Speech Rating Scale: Reliability, Validity, and Utility. AJSLP, 2023. 32(2): p. 469-491.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/regional-atrophy-and-motor-speech-in-psp/