The language profile of posterior cortical atrophy

Abstract

Background: Posterior cortical atrophy (PCA) is typically considered to be a visual syndrome, primarily characterised by progressive impairment of visuoperceptual and visuospatial skills. However, patients commonly describe early difficulties with word retrieval. This paper details the first systematic analysis of linguistic function in PCA. Characterising and quantifying the aphasia associated with PCA is important for clarifying diagnostic and selection criteria for clinical and research studies.

Methods: 15 patients with PCA, seven patients with logopenic/phonological aphasia (LPA) and 18 age matched healthy participants completed a detailed battery of linguistic tests evaluating auditory input processing, repetition and working memory, lexical and grammatical comprehension, single word retrieval and fluency, and spontaneous speech.

Results: Relative to healthy controls, PCA patients exhibited language impairments across all of the domains examined, but with anomia, reduced phonemic fluency and slowed speech rate the most prominent deficits. PCA performance most closely resembled that of LPA patients on tests of auditory input processing, repetition and digit span, but was relatively stronger on tasks of comprehension and spontaneous speech.

Conclusions: The study demonstrates that in addition to the well reported degradation of vision, literacy and numeracy, PCA is characterised by progressive oral language dysfunction with prominent word retrieval difficulties. Overlap in the linguistic profiles of PCA and LPA, which are both most commonly caused by Alzheimer's disease, further emphasises the notion of a phenotypic continuum between typical and atypical manifestations of the disease. Clarifying the boundaries between Alzheimer's disease phenotypes has important implications for diagnosis, clinical trial recruitment and investigations into biological factors driving phenotypic heterogeneity in Alzheimer's disease. Rehabilitation strategies to ameliorate the phonological deficit in PCA are required.

Figure 1

A-C) Regional differences in cortical thickness between A) PCA and controls, B) LPA and controls, and C) LPA and PCA. Colour scales represent FDR-corrected p values thresholded at a 0.05 significance level. Red and yellow represent lower cortical thickness in the patient groups compared with controls, and PCA compared with LPA, whereas dark and light blue represent greater cortical thickness. D) Overlap map of lower cortical thickness in PCA and LPA compared with controls. Blue represents areas which are reduced in PCA only, green shows regions reduced in LPA only, and orange shows areas reduced in both PCA and LPA compared with controls.

Figure 2

Mean composite ranking scores for each participant group across the domains of auditory input processing, repetition/working memory, comprehension, naming/fluency, and spontaneous speech.