Background Simple, robust and clinically meaningful outcome measures are required for neuroprotective trials in Parkinson's disease (PD). We explored the feasibility of using a new composite binary outcome measure of ‘dead or dependent’ in PD clinical trials, using data from an on–going prospective follow–up study of an incident cohort of patients with PD.

Methods Two hundred incident patients underwent annual follow–up, including assessment of the Hoehn and Yahr stage (H&Y) and Schwab and England activities of daily living scale (S&E). Annual scores were converted into binary variables (H&Y<3 versus H&Y≥3, and S&E≥80% versus S&E<80%). A new outcome of ‘dead or dependent’ versus ‘alive and independent’ was also created, with dependence in activities of daily living defined as a S&E<80%. Using these data, sample sizes were calculated for hypothetical three–year randomised control trials (RCTs) of neuroprotective agents in which the trial outcome was either defined by a binary clinical variable, all–cause mortality, or PD–related mortality.

Results The largest sample sizes were required to use PD–related mortality (n=1808 in each study arm), and all–cause mortality (n=713) as the trial outcome. The new outcome of ‘death or dependency’ required the smallest sample size of all the outcome measures (n=261), including the other binary measures (H&Y≥3, n=565; S&E<80%, n=407).

Conclusion ‘Death or dependency’ is a feasible and potentially important new composite outcome measure for PD trials, including neuroprotective trials, although more work needs to be done to confirm this.