Graded, multidimensional intra- and intergroup variations in primary progressive aphasia and post-stroke aphasia

Abstract

Language impairments caused by stroke (post-stroke aphasia, PSA) and neurodegeneration (primary progressive aphasia, PPA) have overlapping symptomatology, nomenclature and are classically divided into categorical subtypes. Surprisingly, PPA and PSA have rarely been directly compared in detail. Rather, previous studies have compared certain subtypes (e.g. semantic variants) or have focused on a specific cognitive/linguistic task (e.g. reading). This study assessed a large range of linguistic and cognitive tasks across the full spectra of PSA and PPA. We applied varimax-rotated principal component analysis to explore the underlying structure of the variance in the assessment scores. Similar phonological, semantic and fluency-related components were found for PSA and PPA. A combined principal component analysis across the two aetiologies revealed graded intra- and intergroup variations on all four extracted components. Classification analysis was used to test, formally, whether there were any categorical boundaries for any subtypes of PPA or PSA. Semantic dementia formed a true diagnostic category (i.e. within group homogeneity and distinct between-group differences), whereas there was considerable overlap and graded variations within and between other subtypes of PPA and PSA. These results suggest that (i) a multidimensional rather than categorical classification system may be a better conceptualization of aphasia from both causes; and (ii) despite the very different types of pathology, these broad classes of aphasia have considerable features in common.

Data-Driven, Visual Framework for the Characterization of Aphasias Across Stroke, Post-resective, and Neurodegenerative Disorders Over Time

“…By evaluating a large cohort of patients suffering from stroke, neurodegenerative, and post-resective aphasia, we have provided a two-dimensional framework that can visualize language impairment across a variety of disease etiologies. While the language tool assessment shared across three cohorts highlights the similarities of aphasia phenotypes across disease etiologies, as with prior dimensionality reduction studies ( 22 ), the proposed framework using only two dimensions also provides sufficient granularity to preserve clinical classifications across all cohorts. This visual method of characterizing an aphasia phenotype provides a simplified and intuitive method of rapidly assessing aphasia phenotypes across populations and time.…”

“…The behavioral similarity mirrors the neuroanatomical similarity, in which peak atrophy for patients with nfvPPA localizes to the left posterior inferior frontal gyrus and adjacent areas ( 3 ). Investigation at higher dimensions or with more detailed behavioral assessments would enable discernment of behavioral differences ( 22 ). For instance, studies of nfvPPA have shown that grammar and fluency can be dissociated; case examples of patients with nfvPPA were found to have near normal fluency but impaired grammar and vice versa.…”

“…Other studies have attempted to subtype PPA variants on a two dimensional template comprised of grammaticality and word comprehension, based on the clinical identification of orthogonal tasks for subtyping ( 36 , 37 ). Only one prior study, Ingram et al ( 22 ), proposed a multidimensional cross-cohort platform, composed of four dimensions. As compared to Ingram et al ( 22 ), this study focused on the development of a two dimensional platform using a screening aphasia battery to provide a single framework for characterizing phenotypes.…”

“…Only one prior study, Ingram et al ( 22 ), proposed a multidimensional cross-cohort platform, composed of four dimensions. As compared to Ingram et al ( 22 ), this study focused on the development of a two dimensional platform using a screening aphasia battery to provide a single framework for characterizing phenotypes. Because this study employed two native dimensions rather than a four factor rotated solution ( 22 ), the interpretations of the dimensions were distinct.…”

“…Second, using this framework, we demonstrate that disease phenotypes can be visually tracked over time. Recent efforts ( 22 ) have demonstrated the feasibility of comparing across patient cohorts using dimensionality reduction techniques; we propose an alternative two-dimensional platform and demonstrate the feasibility of tracking disease attributes over time. Ultimately, this method, combined with more detailed language evaluations shared across cohorts may allow for the interdisciplinary study of complex language networks, by focusing on their similarities rather than their differences.…”