Verbal Short-Term Memory Disturbance in the Primary Progressive Aphasias: Challenges and Distinctions in a Clinical Setting.

David Foxe,Cathleen Taylor-Rubin,James R Burrell,Olivier Piguet,Muireann Irish,Nicholas J Cordato,Sau Chi Cheung,Rebekah M Ahmed

doi:10.3390/brainsci11081060

David Foxe, Cathleen Taylor-Rubin + Show 6 more

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https://doi.org/10.3390/brainsci11081060

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Abstract

Impaired verbal ‘phonological’ short-term memory is considered a cardinal feature of the logopenic variant of primary progressive aphasia (lv-PPA) and is assumed to underpin most of the language deficits in this syndrome. Clinically, examination of verbal short-term memory in individuals presenting with PPA is common practice and serves two objectives: (i) to help understand the possible mechanisms underlying the patient’s language profile and (ii) to help differentiate lv-PPA from other PPA variants or from other dementia syndromes. Distinction between lv-PPA and the non-fluent variant of PPA (nfv-PPA), however, can be especially challenging due to overlapping language profiles and comparable psychometric performances on verbal short-term memory tests. Here, we present case vignettes of the three PPA variants (lv-PPA, nfv-PPA, and the semantic variant (sv-PPA)) and typical Alzheimer’s disease (AD). These vignettes provide a detailed description of the short-term and working memory profiles typically found in these patients and highlight how speech output and language comprehension deficits across the PPA variants differentially interfere with verbal memory performance. We demonstrate that a combination of verbal short-term and working memory measures provides crucial information regarding the cognitive mechanisms underlying language disturbances in PPA. In addition, we propose that analogous visuospatial span tasks are essential for the assessment of PPA as they measure memory capacity without language contamination.

Highlights

Impaired verbal ‘phonological’ short-term memory is considered a cardinal feature of the logopenic variant of primary progressive aphasia and is thought to underpin many of the language deficits in this syndrome [1]
We demonstrate that visuospatial span tasks are essential for the assessment of PPA as they measure memory capacity without language contamination
Considering the semantic variant of PPA (sv-PPA) patient’s profile, we found digit and word span were spared whereas sentence repetition was compromised, likely to be due to his degraded semantic store [3]

Summary

Introduction

Impaired verbal ‘phonological’ short-term memory is considered a cardinal feature of the logopenic variant of primary progressive aphasia (lv-PPA) and is thought to underpin many of the language deficits in this syndrome [1]. Lv-PPA patients display impaired digit, letter, and word span on formal testing but perform normally on singledigit and -word repetition tasks [2,3,4]. These deficits occur in the context of relatively preserved grammar and articulation, phonological paraphasias may be present [1,3]. Verbal short-term memory performance remains relatively spared in the early stages of the semantic variant of PPA (sv-PPA) [3,4] These distinct verbal short-term memory profiles led the international consensus criteria for PPA to include ‘impaired sentence repetition and phrases’ as a core clinical feature of lv-PPA [1]—prompting clinicians to evaluate the verbal short-term memory system when assessing patients with a differential diagnosis of lv-PPA

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