Prevalence of parkinsonism and Parkinson's disease in the Arosa Island (Spain): a community-based door-to-door survey

There are scarce epidemiological data on parkinsonism in Spain. Since the Arosa Island community (Northwestern Spain) has been for centuries relatively isolated, it represents a potentially useful setting to undercover genetic factors with a founder effect, as well as local environmental influences. We performed a one-stage door-to-door survey in the Arosa Island in 2004 to determine the prevalence of parkinsonism and Parkinson's disease (PD) in the population aged 65 years or over. Out of 41 individuals detected with parkinsonism, 15 were diagnosed with PD (36.6%), 13 with drug induced parkinsonism (31.7%), seven with vascular parkinsonism (17.1%), four patients had parkinsonism with associated features (9.8%) and two had unspecified parkinsonism (4.9%). We obtained a crude prevalence rate of parkinsonism of 5.44% (adjusted rate: 4.73%) and a crude prevalence rate of PD of 1.99% (adjusted rate 1.7%); both prevalence rates increased with advancing age. The prevalence rate for parkinsonism was higher than that in similar populations of Spain and other European countries while that for PD was in the range obtained from these populations. Among PD cases, 26.7% (n=4) were undiagnosed before the survey. Most cases of drug-induced parkinsonism were secondary to neuroleptics and had not been previously diagnosed. The relatively high proportion of undiagnosed drug-induced parkinsonisms and PD is surprising in a public health system which is free and universal. The lack of excess of late-onset PD among Arosans does not support the existence of specific genetic or environmental factors contributing to PD in this particular geographical area.