Syndromes dominated by apraxia of speech show distinct characteristics from agrammatic PPA

TLDR

The study aimed to determine whether dominant apraxia of speech (AOS) resembles agrammatic primary progressive aphasia (agPPA) or primary progressive AOS (PPAOS) in clinical and imaging features. The authors compared 67 patients (18 PPAOS, 10 dominant AOS, 9 agPPA, 30 controls) using MRI, DTI, FDG‑PET, PiB‑PET and speech assessments, classifying AOS into type 1 (sound distortions) or type 2 (syllabic prosody). Dominant AOS patients most frequently exhibited type 2 AOS and premotor‑cortex focal atrophy with midbrain loss, mirroring PPAOS, whereas agPPA patients showed type 1 AOS and widespread cortical atrophy, indicating that dominant AOS aligns more closely with PPAOS than with agPPA.

Abstract

<h3>Objective:</h3> We assessed whether clinical and imaging features of subjects with apraxia of speech (AOS) more severe than aphasia (dominant AOS) are more similar to agrammatic primary progressive aphasia (agPPA) or to primary progressive AOS (PPAOS). <h3>Methods:</h3> Sixty-seven subjects (PPAOS = 18, dominant AOS = 10, agPPA = 9, age-matched controls = 30) who all had volumetric MRI, diffusion tensor imaging, F18-fluorodeoxyglucose and C11-labeled Pittsburgh compound B (PiB)-PET scanning, as well as neurologic and speech and language assessments, were included in this case-control study. AOS was classified as either type 1, predominated by sound distortions and distorted sound substitutions, or type 2, predominated by syllabically segmented prosodic speech patterns. <h3>Results:</h3> The dominant AOS subjects most often had AOS type 2, similar to PPAOS. In contrast, agPPA subjects most often had type 1 (<i>p</i> = 0.01). Both dominant AOS and PPAOS showed focal imaging abnormalities in premotor cortex, whereas agPPA showed widespread involvement affecting premotor, prefrontal, temporal and parietal lobes, caudate, and insula. Only the dominant AOS and PPAOS groups showed midbrain atrophy compared with controls. No differences were observed in PiB binding across all 3 groups, with the majority being PiB negative. <h3>Conclusion:</h3> These results suggest that dominant AOS is more similar to PPAOS than agPPA, with dominant AOS and PPAOS exhibiting a clinically distinguishable subtype of progressive AOS compared with agPPA.