A two-fold difference in the age-adjusted prevalences of Parkinson's disease between the island of Als and the Faroe Islands

With the aim of comparing the previously found high prevalence of idiopathi c Parkinson's disease (PD) in the Faroe Islands with the prevalence of PD i n an area of Denmark, we used the same case-finding methods for case ascert ainment and the same strict criteria to diagnose PD on the island of Als. D uring the last year before the prevalence date (1 January 1998), we found i n various registries from pharmacies, hospital, private neurologist and gen eral practioners 121 patients with suspected Parkinsonism out of 56 839 inh abitants on the island of Als. After exclusion of those who had other disea ses, a total of 79 patients were left for further examinations. Among these we found 58 with PD. The overall prevalence of PD was estimated to be 102. 0 and the age-adjusted prevalence to be 98.3 per 100 000 persons compared w ith 187.6 and 209.0 in the Faroe Islands. Compared with the previous result s from the Faroe Islands (prevalence date 1 July 1995) we found an even low er mean age at onset of PD symptoms and at onset of treatment, a lower prop ortion of definite PD and a lower average dose of levodopa. We therefore co nclude that the two-fold higher prevalence in the Faroe Islands than on the island of Als was not due to an early diagnosis and a higher ascertainment of cases with mild PD, which was suggested as being one possible explanati on for our previous finding of a high prevalence of PD in the Faroe Islands .