Can we differentiate the primary progressive aphasias using visuospatial tests?

Abstract Introduction: Primary progressive aphasias (PPA) comprise three main variants: logopenic (lv-PPA), non-fluent (nfv-PPA) and semantic (sv-PPA). Differentiating the language profiles of the PPA variants remains challenging, especially for lv-PPA and nfv-PPA. As such there are advantages to using diagnostic tools that do not rely on speech and language. Here, we investigated the visuospatial short-term and working memory profiles of the PPA variants and typical Alzheimer’s disease (AD). When comparing the PPA variants, we hypothesised the lv-PPA and AD groups would have the most difficulty on these tasks and that this would relate to the integrity of posterior temporal and parietal brain regions. Method: Thirty-three lv-PPA, 26 nfv-PPA, 31 sv-PPA and 58 AD patients, and 45 matched healthy controls were recruited. All participants completed the WMS-III Spatial and Digit Span tasks and underwent a structural brain MRI for voxel-based morphometry analyses. Results: Spatial Span Forward (SSF) performance was impaired in lv-PPA but not in nfv-PPA or sv-PPA. In contrast, Digit Span Forward (DSF) performance was similarly impaired in lv-PPA and nfv-PPA, and preserved in sv-PPA. As expected, backward span scores were significantly lower for all groups. Neuroimaging analyses revealed that SSF and SSB performance in all patients combined correlated with grey matter loss in several clusters located in temporo-parieto-occipital brain regions. Post-hoc group comparisons of these regions showed that grey matter loss was more extensive in the lv-PPA and AD groups than the nfv-PPA and sv-PPA groups. Conclusion: The findings suggest that the visuospatial short-term and working memory profiles of the PPA variants are separable and likely reflect their distinct patterns of brain atrophy.