title: Incidence of Parkinson's disease in Norway: the Norwegian ParkWest study.
abstract: OBJECTIVE
  To present the incidence of Parkinson's disease (PD) in Norway and to explore gender influences on incidence and age at onset, as well as severity and pattern of parkinsonism at the time of diagnosis in a representative drug naïve cohort with newly diagnosed PD.
  
  
  METHODS
  In four Norwegian counties comprising a base population of 1 052 075 inhabitants, multiple sources of case ascertainment and a four step diagnostic procedure were used to establish a representative cohort of patients with incident PD at a high level of diagnostic accuracy. Of a total of 604 subjects referred to the study, 265 individuals fulfilled the clinical research criteria of PD at their latest clinical visit, at a mean 28 months after identification.
  
  
  RESULTS
  The incidence of PD in the study area, age standardised to the 1991 European standard population, was 12.6/10(5yr-1) (95% CI 11.1 to 14.2). The overall age standardised male to female ratio was 1.58 (95% CI 1.22 to 2.06), with a consistent male preponderance throughout all age groups. Clinical onset of PD was later in women than in men (68.6 vs 66.3 years; p = 0.062) whereas severity and pattern of parkinsonism in drug naïve patients was not different between genders at the time of diagnosis.
  
  
  CONCLUSIONS
  Incidence rates of PD in Norway are similar to those in other Western European and American countries. Female gender was associated with a considerably lower risk of PD and slightly delayed motor onset but had no impact on severity of parkinsonism or clinical phenotype in incident drug naïve PD, suggesting that the female gender influences on the nigrostriatal system are most pronounced in the preclinical phase of the disease.
authors.affiliation: The Norwegian Centre for Movement Disorders, Stavanger University Hospital, PO Box 8100, N-4068 Stavanger, Norway. algu@sus.no
authors.forename: G
authors.initials: G
authors.lastname: Alves
authors.forename: B
authors.initials: B
authors.lastname: Müller
authors.forename: K
authors.initials: K
authors.lastname: Herlofson
authors.forename: I
authors.initials: I
authors.lastname: HogenEsch
authors.forename: W
authors.initials: W
authors.lastname: Telstad
authors.forename: D
authors.initials: D
authors.lastname: Aarsland
authors.forename: O-B
authors.initials: OB
authors.lastname: Tysnes
authors.forename: J P
authors.initials: JP
authors.lastname: Larsen
mesh_terms: D000328:Adult; D000367:Age Factors; D017668:Age of Onset; D000368:Aged; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D010300:Parkinson Disease / Q000175:diagnosis / Q000453:epidemiology*; D011446:Prospective Studies; D012737:Sex Factors