Parkinson's disease occurrence in Europe.

Parkinson's disease (PD) surveys and death-record studies in European populations were reviewed. Particular attention was given to methodological aspects. Two sets of quality criteria were used. Four door-to-door surveys revealed underdiagnosis of prevalent idiopathic parkinsonism ranging from 30% to 71%. Quality surveys based on medical records were scarce. The analysis of a) the time relationships between the diagnostic process and the study period for measurements, and b) a variation observed in the shape of the curve for age-specific prevalences, suggested that both incidence and prevalence were underestimated by these surveys, especially among the elderly. In the UK, Denmark and Sweden, mortality from parkinsonism increased over time for ages over 70 years, but decreased for the younger age groups. A two-fold variation in mortality was found between countries. It is concluded that PD is widely distributed in Europe, and that most geographical differences in reported disease occurrence can be explained by methodological variations in measurements. The pattern of variation of age-specific figures was similar for mortality and prevalence. This might reflect decreasing prevalences among those aged under 70 years and increasing ascertainment in the elderly. There is a need for research methods for specific purposes in this field to be developed.