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Background The purpose of this study was to determine the extent to which summary index scores from the short form Parkinson's Disease Questionnaire (PDQ-8) replicate those from the parent form (PDQ-39) in a longitudinal study. Methods Longitudinal data gained from the PD-MED trial were examined (n = 1867), to determine the extent the PDQ-8 replicates results from the PDQ-39 at baseline and follow up. The sensitivity to change of the PDQ-8 was also compared with that of the PDQ-39. Finally, results on the two measures were compared with those from the Hoehn and Yahr (HY) clinical staging scale. Results Results of the Single Index summary score gained from the PDQ-8 were found to closely replicate those gained from the PDQ-39 at each of the three time points. Furthermore at each time point the intraclass correlation coefficient between the two measures was very high (ICC range 0.93–0.96). Similarly, the two measures gave very similar accounts of change (e.g. from baseline to follow up at one year effect sizes were 0.18 for the single index calculated using the PDQ-39, and 0.09 when calculated using the PDQ-8). Similar levels of correlation were found between the two indices when correlated with the HY scale. Conclusions The PDQ-8 closely replicates results gained from the PDQ-39 when calculating single indices. In instances where a single summary score of the impact of PD on self-reported quality of life is needed, it is likely the PDQ-8 will provide reliable and accurate information.

Background There is no consensus on the association between exposure to hydrocarbons and the risk of Parkinson's disease (PD). We conducted a systematic review and meta-analysis to summarise the epidemiological evidence and included a new large case-control study. Methods Data were extracted following a predefined protocol. Risk estimates regarding the association between hydrocarbon exposure and PD were consolidated to produce a summary odds ratio (OR), 95% confidence intervals (CI), and p-value. In our case-control study, 1463 PD patients and 685 controls were recruited from clinical trials and completed a structured questionnaire describing their previous working exposure to hydrocarbons and other demographic measures. The association between exposure to hydrocarbons and risk of PD was evaluated using logistic regression. Results The systematic search identified 13 case-control studies matching the inclusion criteria. The meta-analysis included 3020 PD cases and 6494 controls. The summary OR was 1.32 (95% CI 1.08–1.62, p = 0.006) for hydrocarbon exposure (ever versus never). In the PD GEN study, occupational exposure to hydrocarbons significantly increased the risk of PD (OR = 1.61; 95% CI 1.10–2.36, p = 0.014), and risk dose-dependently increased for subjects exposed greater than 10 years compared to subjects never exposed (OR = 2.19; 95% CI 1.13–4.26, p = 0.021). The addition of PD GEN data increased the total numbers to 4483 PD cases and 7179 controls and strengthened the significant association (summary OR = 1.36; 95% CI 1.13–1.63, p = 0.001). Conclusions This systematic review supports a positive association between hydrocarbon exposure and PD. Data from prospective studies are required to reinforce the relationship between hydrocarbon exposure and PD.