Study of the prevalence of Parkinson's disease using dopamine transporter imaging

To investigate the prevalence of Parkinson's disease (PD), a three-phase study was conducted.

In phase 1, standardized interviews were performed in a random sample of elderly aged 65 years or older using a questionnaire. In phase 2, neurological examinations were performed to clinically diagnose PD. In phase 3, dopamine transporter (DAT) imaging was performed to support the clinical diagnosis. After the three-phase study, longitudinal clinical observation was performed.

A total of 714 subjects participated in the phase-1. Two hundred and twenty-two subjects, scored more than two points, were referred to the movement disorder specialist. Eighteen of these subjects showed overt or equivocal parkinsonian features. Three subjects were clinically diagnosed with possible PD: five with essential tremor with equivocal extrapyramidal signs, eight with frontal-subcortical gait disorder and two with drug-induced parkinsonism. The three subjects with possible PD showed a typical PD pattern of reduced DAT density. DAT density was normal in the other 15 subjects. Results of long-term follow-up supported the diagnoses. The crude prevalence of PD was 0·42 per 100 persons.

During the clinical evaluation, we encountered a very large proportion of subjects with equivocal parkinsonian features, who posed a diagnostic challenge and a substantial risk of misestimating the prevalence of PD. The combination of DAT imaging and longitudinal clinical observation of equivocal cases enabled us to differentiate PD from other conditions. We suspect that the variation in estimates of the prevalence of PD may be attributable to a considerable proportion of subjects with equivocal parkinsonian features and how they are evaluated.