Incidence of Parkinson's disease and parkinsonism in northern Sweden: a population-based study.

The differential diagnosis of parkinsonian disorders is difficult, especially early in the course of the diseases. The clinical subtypes of Parkinson's disease (PD) have not so far been described in newly diagnosed patients. We present a prospective incidence cohort study of patients with idiopathic parkinsonian syndromes in the Umeå region in northern Sweden identified over a 4-year period. The clinical diagnoses were re-evaluated at follow-up visits at 12 months. We found 138 patients with parkinsonism: 112 PD, 12 multiple system atrophy with predominant parkinsonism (MSA-P), six progressive supranuclear palsy (PSP) and eight unclassifiable patients. The crude incidences for all age ranges per 100,000 were: PD 19.7 (95% confidence interval 16.1-23.3); MSA-P 2.1 (1.1-3.7); PSP 1.1 (0.4-2.4); idiopathic parkinsonism 24.3 (20.2-28.4). Age-standardized to the average Swedish population 2004-2007: PD 22.5 (18.3-26.7); MSA-P 2.4 (1.2-4.2); PSP 1.2 (0.4-2.6); idiopathic parkinsonism 27.5 (22.9-32.1). The crude annual incidence rate for PD, with exclusion of patients with normal dopamine receptor uptake (FP-CIT-SPECT), was 18.8 per 100,000 (95% confidence interval 15.2-22.4), age-adjusted to the average Swedish population 2004 to 2007: 21.5 (17.4-25.6). The incidence rates did not differ significantly between men and women. The cumulative incidence of PD up to 89 years of age was for men 3.4%, for women 2.6%, and for both sexes combined 2.9%. The annual incidence rates found for PD, idiopathic parkinsonism, MSA-P and PSP are among the highest reported.