SENSE-Cog Lewy: Investigating the Impact of Sensory Loss on the Diagnosis, Clinical Features and Prognosis of Lewy Body Dementia

Abstract Background Lewy Body Dementia (LBD) accounts for 20% of the nearly 65,000 people with dementia in Ireland, but fewer than 5% of those affected receive a formal diagnosis. LBD includes both Parkinson’s disease dementia (PDD) and dementia with Lewy bodies (DLB) and can be characterised by fluctuating and progressive cognitive difficulties, vivid visual hallucinations and REM sleep behaviour disturbances. Sensory function such hearing, vision and olfactory function declines with age—but increasing evidence shows that abnormal patterns of sensory dysfunction can be one of the earliest clinical signs and predictors of progression of neurodegenerative diseases such as Lewy body dementia and Parkinson’s disease dementia. Methods A scoping review was undertaken using Embase, CINAHL, PsychINFO and PubMed. Only reports on people with LBD (DLB and PDD) from any stage, prodromal to late stage were considered. Papers primarily addressing other forms of neurocognitive disorders were excluded. Sensory loss was conceptualised as the loss of smell, vision and hearing. Two reviewers independently assessed each study for inclusion, and disagreements were resolved by a third reviewer. Results Reports on sensory loss in LBD were very few and most often were comparing sensory loss across different dementia types. Strong associations were observed between olfactory loss and particular visual impairment patterns and the severity of both cognitive and non-cognitive DLB symptoms. Olfactory impairment is a potential early biomarker of DLB and PDD and severity of olfactory dysfunction can predict cognitive decline. Visual hallucinations, for example, were found to be closely linked to visual impairment patterns such as pareidolia. Conclusion This study highlights a knowledge gap regarding the patterns of sensory loss in LBD and their relationship with cognitive and non-cognitive LBD symptoms. Sensory assessments represent potentially valuable diagnostic and prognosis tool in LBD, with further research required to understand the aetiological mechanisms underlying sensory impairment in LBD and other dementias.