Sleep Disorders in Neurodegenerative Diseases with Dementia: A Comprehensive Review

Dementia is a growing problem of global relevance, currently affecting over 55 million people worldwide. The number of new dementia cases is still increasing, primarily due to the aging of society. Dementia is defined as a substantial decline in cognitive function, and it is inherently associated with neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, dementia with Lewy bodies, frontotemporal dementia, and vascular dementia. Of note, most patients suffering from neurodegenerative conditions, in addition to cognitive impairment, often experience various types of sleep disorders, including insomnia, rapid eye movement sleep behavior disorder, sleep-disordered breathing, and circadian rhythm disturbances. There is increasing evidence of a bidirectional interaction between sleep disturbances and mental health. Disrupted sleep may directly aggravate neuropsychiatric symptoms, like depression, anxiety, agitation, and hallucinations, and conversely, such symptoms can make sleeping more difficult. This creates a feedback loop that inevitably leads to disease progression and deterioration in quality of life. In this review, we provide an up-to-date overview of the nature and mechanisms behind sleep disorders in major neurodegenerative diseases, summarize treatment strategies for handling sleep disturbances, and discuss the clinical relevance of sleep-mental health interactions in the context of neurodegeneration-associated dementia. Neurodegeneration is a complex problem on the border between neurology and psychiatry, and it poses a challenge to the healthcare system, as it requires multidisciplinary approaches for optimal management. Understanding the connection between sleep and neuropsychiatric symptoms offers further opportunities for better symptom control, improved quality of life, and slower cognitive decline.