Active and Passive Methods of Detecting Parkinson's Disease

Field: Medicine (Health Sciences)

To the Editor: Previous studies of the early detection of idiopathic Parkinson's disease (IPD) raised the possibility of introducing population-based screening to detect IPD in the early stage.1 It is therefore of great interest to assess the IPD detection rates of different methods. To the knowledge of the authors, no population-based data are available to compare different case-finding methods in IPD detection. In 2001, the Keelung Community-based Integrated Screening (KCIS) program offered a one-stage neurological survey (active detection method) for half of the residents who attended the KCIS program by random selection of screening activities. Limited access to neurologists meant that the other community residents were diagnosed with IPD using a conventional case-finding method (passive detection method). Thus, a natural experiment similar to a randomized controlled trial provided an opportunity to compare the detection rates of active and passive methods of detecting IPD. Enrolled subjects were obtained from participants in the KCIS program, described in full elsewhere.2 Of 20,951 residents aged 40 and older, 11,332 were administered the active detection method and the remaining 9,621 subjects the passive detection method. Seventy-one IPD cases diagnosed before 2001 in the active detection group and 45 in the passive detection group were excluded. Neurologists evaluated each participant in the active detection group for IPD using a standardized diagnostic protocol; 62 cases were detected in 2001. The remaining participants were followed by linkage of these screenees with national health insurance (NHI) claim records to track potential diagnosis of IPD between 2001 and 2004. For the passive method, screenee data for 2001 to 2004 were examined to estimate IPD incidence rate according to year by linking with the NHI claim records. The neurologists confirmed the Hoehn-Yahr (H-Y) stage of the 62 IPD cases diagnosed in 2001. Sixty-one of the remaining 250 IPD cases diagnosed using linkage with NHI claims records were further sampled to confirm their H-Y stage using chart review. Distribution of early- (H-Y Stage I or II) and late-stage (H-Y Stage III or greater) according to the two detection methods was compared. The cumulative detection rate was calculated by adding up each year's detection rate of IPD. The risk ratio of being at Stage III or greater for active detection method as opposed to passive detection method was calculated using the Poisson method. Two hundred nine IPD cases were detected using the active detection method and 103 using the passive detection method. The cumulative detection rate for the two groups is shown in Figure 1A. The active method was able to detect 1.7 times as many (95% confidence interval (CI) = 1.35–2.34) IPD cases as the passive method (P < .001). In the active detection group, 82.7% of IPD cases were detected in an early H-Y stage. In the passive detection group, 52% IPD cases were diagnosed in the early stage (Figure 1B). The risk ratio of being at H-Y Stage III or greater for the active versus passive detection method was 0.36 (95% CI = 0.20–0.65). The active detection method could reduce 64% (95% CI = 35–80%) of IPD cases from H-Y Stage I to Stage III. Although door-to-door surveys seemed to yield higher prevalence rates than record-based studies,3 no study has directly elucidated the differences between case-finding methods and compared different methodologies of determining IPD. The current study directly proved that the active method detects 1.7 times as many IPD cases as the passive method. In addition, the study design was able to overcome the potential discrepancies of previous epidemiological studies. A previous study found that subjects in H-Y Stage I may have the same life expectancy as the general population.4 Early detection and treatment of IPD may increase life expectancy.5-8 One study found that IPD cases detected early had a 51% lower incidence of Stage III or greater and 25% lower mortality.4 The results of the current study suggest that the active detection method identified more Stage I and II IPD cases (82.7%) than did the NHI claims records (52%, P = .003). In addition, the active detection method could reduce the incidence of IPD cases at H-Y Stage III or greater at diagnosis by 64%. The active detection method is more time consuming and requires more resources, but delayed treatments may result in rapid progress in H-Y stage and much greater costs to treat complications that accompany disease progression.9, 10 The cost effectiveness and benefit of the active and passive detection methods need further evaluation. We acknowledge the assistance of our colleagues in the Bureau of Health in Keelung City for implementing the KCIS program. Conflict of Interest: All authors have no conflicts of interest. Author Contributions: Chiung-Jung Wen: data analysis, interpretation, literature search, figures, writing. Amy Ming-Fang Yen: data collection and analysis. Sherry Yueh-Hsia Chiu, Sam Li-Sheng Chen, Jean Ching-Yuan Fann: data interpretation, light editing. Yuarn-Chung Hwang, Ta-Fu Chen, Ying-Rong Wen: data collection. Horng-Huei Liou: study design, data collection and interpretation, substantial editing of manuscript. Hsiu-Hsi Chen: study design, data collection, data interpretation, final editing of manuscript. Hsiu-Hsi Chen had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Sponsor's Role: None.