When it is not primary progressive aphasia: A scoping review of spoken language impairment in other neurodegenerative dementias

Abstract

Background: Progressive difficulties with spoken language occur across the spectrum of degenerative dementia. When not a primary presenting and dominant symptom, language difficulties may be overlooked in favor of more prominent cognitive, behavior, or motor deficits. The aim of this scoping review is to examine the extent and nature of the research evidence describing (1) the spoken language impairments found in non-language led dementias, (2) their impact on everyday living, and (3) the reported language interventions.

Methods: We searched PubMed, MEDLINE, OVID-EMBASE, PsycINFO, and SpeechBITE using terms related to spoken language for the following dementia types: Parkinson's disease dementia (PDD), dementia with Lewy bodies (DLB), progressive supranuclear palsy (PSP), cortico-basal syndrome (CBS), behavior variant frontotemporal dementia (bvFTD), early-onset Alzheimer's disease (EOAD), posterior cortical atrophy (PCA), and motor neuron disease associated with FTD (MND+FTD). Risk of bias was assessed with the QualSyst tool.

Results: Seventy-three eligible studies were included. A wide range of spoken language impairments were reported, involving both linguistic (e.g., syntactic processing) and other cognitive (e.g., sustained attention) underlying mechanisms. Although the severity of these deficits was scarcely reported, in some cases they manifested as non-fluent, dynamic, and global aphasias. No papers in the review described either the impact of these language impairments on everyday living or language therapies to treat them.

Discussion: There is a need to understand better the level of disability produced by language impairment in people living with non-language-led dementias. Our findings suggest three calls for action: (1) research studies should assess the clinical relevance of any spoken language deficits examined, (2) both linguistic and cognitive underlying mechanisms should be fully described (to inform the design of effective language and behavioral interventions), and (3) trials of language therapy should be conducted in those groups of individuals where significant language impairment is proved.

Keywords: aphasia; communication disorders; dementia; language therapy; spoken language.

FIGURE 1

PRISMA flow diagram

FIGURE 2

Overview of the distribution of studies according to design and quality. A, Studies by design. Case‐report are considered studies where n = 1; case series are studies in which the paper contains multiple case reports; cohort studies were considered longitudinal studies of a group of patients (a case series followed over time); cross‐sectional studies were defined as a group of patients examined at one point in time (or multiple groups of patients at one point in time); case‐control studies corresponded to cross‐sectional study that compared to a healthy group or other disease group. B, Studies by quality. The definition of quality based on the summary score (SS) obtained on Standard Quality Assessment Criteria for Evaluating Primary Research Papers from a Variety of Fields (QualSyst) is strong (SS of >80), good (SS of 71–79), adequate (SS of 50–70) and limited (SS of <50)