Objective: To investigate possible long-term changes in the incidence of Parkinson’s disease (PD) in rural regions.

Background: Living in rural areas has long been suspected to increase the risk of PD. Rural living, agricultural occupation or well water drinking are possible proxies to a common nominator, such as pesticide exposure that could trigger PD pathogenesis via mitochondrial damage. During recent years, a global process of urbanization has paralleled a reallocation of labor from agriculture to other sectors and a large decrease in pesticide use. We hypothesized that these changes have decreased PD incidence in rural areas.

Methods: We compared annual age-standardized PD incidences of 317 urban and rural regions in Finland from an 18-year period (1997 to 2014). The total annual population in the analysis was 5.2-5.5 million with 26 731 new cases of PD. Regions were classified as rural or urban using population-based (<15 000 vs. >30 000) and production-based (<5% vs. >5% of work force in primary production) categorization. Annual regional PD incidences were derived from the Finnish National Prescription Register. Age-standardized incidence rates for each region and year were calculated using the EU standard population as reference.

Results: Age-adjusted incidence of PD was higher in rural areas over the entire study period (rural 33.2 vs. urban 30.9 per 100 000 person-years; incidence rate ratio=1.08, p<0.0001). The incidence increased in both rural and urban areas over 18 years, but there were no significant differences in the slopes (p=0.28) indicating no regional differences in the trend in IRs. The results were essentially the same using production-based classification of regions.

Conclusions: The current age-adjusted risk of PD in Finnish rural areas remains higher compared to urban areas and the incidence is on the rise in all regions. Rural-to-urban incidence rate ratio has not decreased. Either the specific rural risk factors have remained constant, the gradual reduction in incidence is too slow to be detected in 18 years, or the process is associated with a long latency period.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/long-term-incidence-of-parkinsons-disease-in-rural-areas-of-finland/