Natural history and effectiveness of early detection of Parkinson's disease: results from two community-based programmes in Taiwan (KCIS no. 11).

Objectives: The natural course of Parkinson's disease (PD), as measured on the Hoehn-Yahr (H-Y) scale, and the impact that early detection would have on prognosis for those with the disease, has barely been addressed since the introduction of L-dopa. This study aimed to elucidate the natural history of PD and effectiveness of early detection in reducing advanced disability and mortality.

Method: A total of 21 362 participants aged 40 years or older were invited to two community-based programmes for the early detection of PD. The step-by-step annual progression rates from H-Y stage I to stage IV or V, and cumulative survival rates, by the H-Y scale, were estimated and applied to simulated data to assess the impact of different screening intervals upon stage at diagnosis and subsequent survival.

Results: The average duration in stages I, II and III was estimated as 2.83, 6.62 and 1.41 years, respectively. The average delay time before deteriorating into H-Y stage III was 9.45 year. Application of these parameters to simulated model predicted a 36% (95% CI: 28-39%), 26% (95% CI: 20-32%) and 19% (95% CI: 13-24%) reduction in death for annual, 5-yearly and 10-yearly screening programmes, respectively.

Conclusion: The present study recommended a 5-yearly screening programme, with 74% of PD cases prevented from progressing to H-Y stage III or worse within 10 years of diagnosis, and leading to a corresponding 26% reduction in mortality.