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Tesi etd-03302017-230105

Thesis type
Tesi di dottorato di ricerca
The role of sleep in cognitive decline
Settore scientifico disciplinare
Corso di studi
tutor Dott.ssa Bonanni, Enrica
Parole chiave
  • mild cognitive impairment
  • sleep
  • cognitive decline
  • cyclic alternating pattern.
Data inizio appello
Data di rilascio
Riassunto analitico
Since the population is getting older in Western countries and the percentage of elderly subjects is increasing, a broad interest is developing towards neurological disease of aging, particularly dementia. Several conditions of increased risk of dementia have been identified; the principal one being mild cognitive impairment (MCI). MCI has been defined as a transitional state between normal aging and dementia, of which may represent a prodrome. The specific transition between normal ageing and MCI can be quite subtle and the distinction between MCI and early dementia can be challenging. <br>The aims of the first study (epidemiological) were (1) to evaluate the prevalence of sleep disturbances in an elderly population and (2) to study their relationship with chronic medical, psychiatric and neurological conditions.<br>Subjects were participants of a population-based study of older adults for dementia and mild cognitive impairment screening in Lunigiana. 2137 subjects (age range 65–85 years, 961 males and 1176 females) were identified as eligible. All patients underwent a clinical interview and answered a questionnaire about insomnia, sleepiness, snoring, sleep apnea and other sleep disturbances. In addition, subjects were administered the Mini Mental State Examination (MMSE), the Beck Depression Inventory and the Memory Assessment Clinic-Q (MAC-Q) by trained physicians. <br>Insomnia symptoms were reported in 63,8% of the study population. The most common sleep complaint was “early awakening” reported by nearly half of the subjects (46,6%), 200 patients presented an insomnia syndrome (11,2%). Almost one quarter of the subjects (24,6%) presented excessive sleepiness, while snoring affected 20,5% of the population and sleep apnoea 3,4%. Leg jerks were reported in 21,2 % of the subjects and other night-time disturbances like sleepwalking, nightmares, bed wetting and falling out of bed were reported by a small portion of participants 0,6%, 4,6%, 0,3%, 0,3% respectively. <br>MMSE as a continuous variable correlated with maintenance insomnia (p=0.04), daytime consequences of insomnia (p=0.04), excessive daytime sleepiness (p=0.03), leg jerks (p=0.03). <br>Univariate analysis of insomnia syndrome with number of comorbidities shows that having more comorbidities was related with an increased incidence of insomnia syndrome that increase from 8% (no comorbidities) to 21% (3 or more comorbidities) with an OR of 1.25.<br>Our results confirm that sleep problems are very common in elderly subjects and closely related to medical and psychiatric illnesses. Since mutual influences of nocturnal sleep problems and medical diseases have been proposed, comorbid sleep disorders should be fully evaluated by the clinician and should not be under diagnosed and under treated.<br><br>The aims of the second study (polysomnographic) were (1) to evaluate sleep variables (both conventional and microstructural) in subjects with MCI, and (2) to prospectively evaluate if and which sleep variables could predict evolution in dementia. <br>Nineteen subjects with MCI (mean age 68.5±7.0 years) and 11 cognitively intact healthy elderly individuals (mean age 69.2±12.6 years) underwent ambulatory PSG for the evaluation of nocturnal sleep architecture and CAP parameters. MCI subjects were clinically evaluated after two years of follow up in order to evaluate the eventual conversion to dementia and, according with status at follow up, subjects were divided into MCI converters and non converters. After 2 years of follow up, 11 MCI converted in dementia (57,8%).<br>Sleep architecture analysis suggested the presence of disturbed sleep in MCI with a significant reduction of REM sleep, of CAP rate and CAP slow components (A1 index) in MCI compared to cognitively intact elderly subjects. A2 and A3 subtypes (arousal-related fast components) increased as a percentage. Sleep architecture analysis did not show significant differences between the two subgroups of MCI, except for an increased REM Latency in MCI converters. CAP analysis showed a significantly decreased CAP rate, A1 index and A3 index in MCI converters vs non converters. Results of study 2 confirm that sleep is impaired in MCI, at both macro and microstructural levels, in line with previous studies reporting sleep alterations associated with neurodegeneration. <br>In conclusion our results suggest that sleep parameters and related alterations might contribute to elucidate the mechanism underlying the interplay between sleep cognitive function and cognitive decline in the context of neurodegeneration and may be considered as biomarkers in the diagnosis and prognosis of early-onset cognitive impairment. <br>