title: Sleep disorders and the natural history of Parkinson's disease: the contribution of epidemiological studies.
abstract: BACKGROUND
  Sleep disorders (SD) are one of the most frequent non-motor manifestations of Parkinson's disease (PD). Recent studies showed that SD may precede the onset of PD.
  
  
  OBJECTIVE
  We reviewed current literature concerning 1) the incidence of PD among subjects with SD; and 2) the occurrence and possible clinical correlations of SD during the course of PD.
  
  
  METHODS
  A Medline search found 17 longitudinal studies.
  
  
  RESULTS
  The incidence of PD among patients with rapid eye-movement sleep behavioural disorders ranged from 20% to 65% of cases, within a wide interval of time (range: 2.2-13.3). The incidence of SD during PD progressively increased with disease duration in population-based studies but presented marked fluctuations in clinical based studies. Older age, male gender, dopaminergic treatment with higher dosage, cognitive impairment and hallucinations were associated with the onset of SD during PD. In the only population-based study among Japanese men excessive daytime sleepiness was associated with a threefold increased risk of developing PD.
  
  
  CONCLUSIONS
  Available data suggest that SD could be the heralding clinical manifestation or a risk factor for PD onset. The prevalence of SD increases during the course of the PD and may be related to specific phenotype and rapid progression of PD. However, the current data are limited because of limited sample size and poor study design; prospective studies with larger sample size are warranted.
authors.affiliation: Azienda Ospedaliero-Universitaria Ospedali Riuniti, Medical and Neurological Sciences, Clinic of Nervous System Diseases, University of Foggia, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Zoccolella
authors.forename: Mariantonietta
authors.initials: M
authors.lastname: Savarese
authors.forename: Paolo
authors.initials: P
authors.lastname: Lamberti
authors.forename: Raffaele
authors.initials: R
authors.lastname: Manni
authors.forename: Claudio
authors.initials: C
authors.lastname: Pacchetti
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Logroscino
mesh_terms: D015897:Comorbidity; D006970:Disorders of Excessive Somnolence / Q000175:diagnosis / Q000453:epidemiology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D020447:Parasomnias / Q000175:diagnosis / Q000453:epidemiology; D010300:Parkinson Disease / Q000453:epidemiology*; D015995:Prevalence; D011597:Psychomotor Performance; D011788:Quality of Life; D012148:Restless Legs Syndrome / Q000175:diagnosis / Q000453:epidemiology; D012720:Severity of Illness Index; D007319:Sleep Initiation and Maintenance Disorders / Q000175:diagnosis / Q000453:epidemiology; D012893:Sleep Wake Disorders / Q000175:diagnosis* / Q000453:epidemiology*; D011795:Surveys and Questionnaires