Sleep disturbance associated with temporal lobe degeneration in frontotemporal dementia

Abstract

AbstractBackgroundSleep abnormalities are increasingly recognized as markers and potential drivers of neurodegenerative proteinopathies. However, the sleep phenotype of less common dementias remains poorly characterised. In particular, clinical experience suggests that patients with focal temporal lobe degeneration in the frontotemporal dementia spectrum can experience sometimes striking sleep disruption. We recently had the opportunity to corroborate this clinical impression in a small series of representative patients participating in a larger cohort study.MethodsTo date, we have studied seven patients and three healthy age‐matched controls. The patients’ diagnoses comprise behavioural variant frontotemporal dementia associated with focal right temporal lobe atrophy (n = 3), semantic dementia associated with focal left temporal lobe atrophy (n = 2), young onset Alzheimer’s disease and logopenic aphasia (each n = 1). No participant had a past history of a clinical sleep disorder. Detailed data on sleep patterns, adapted standard sleep questionnaires (Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale), overnight oximetry and neuropsychological test scores (covering domains of executive function, emotion processing, memory, and auditory perceptual learning) pre‐/post‐overnight sleep were collected with the assistance of patients’ caregivers.ResultsTwo patients with right temporal lobe atrophy and one with left temporal lobe atrophy had marked sleep fragmentation, in one right temporal case accompanied by frequent sleep attacks, with increased overall time in bed and/or attempting to sleep. Epworth and Pittsburgh indices in these patients indicated significant daytime sleepiness and reduced sleep quality; none had evidence of significant sleep apnoea on overnight oximetry. Comparatively mild clinical sleep disturbances were reported in patients with other dementia diagnoses. However, there was evidence for reduced auditory perceptual learning benefit from overnight sleep relative to healthy older controls, particularly in the patients with underlying Alzheimer pathology.ConclusionsThese preliminary findings suggest that focal temporal lobe degeneration may be associated with clinically relevant sleep disruption, as part of the more pervasive derangement of homeostasis in these syndromes. Further work is indicated to define the hypnic phenotype in detail, with sleep electrophysiology and correlative behavioural, neuroimaging and laboratory data in larger patient cohorts.