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 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 4-step diagnostic procedure were used to establish a representative cohort of patients with incident PD at a high level of diagnostic accuracy. Of totally 604 subjects referred to the study, 265 individuals fulfilled clinical research criteria of PD at their latest clinical visit at mean 28 months after identification.
Results: The incidence of PD in the study area, age-standardized to the 1991 European standard population, was 12.6/105yr-1 (95% CI 11.1 – 14.2). The overall age-standardized male-to-female ratio was 1.58 (95% CI 1.22 – 2.06), with a consistent male preponderance through all age groups. Clinical onset of PD was later in women than 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 time of diagnosis.
Conclusion: Incidence rates of PD in Norway are similar to those in other Western-European and American countries. Female gender was associated with considerable lower risk for PD and slightly delayed motor onset but had no impact on severity of parkinsonism or clinical phenotype in incident drug-naïve PD, suggesting that female-gender influences on the nigrostriatal system are most pronounced in the preclinical phase of the disease.