Parkinson's disease dementia (PDD) has become an increasing area of research as treatments for the motor features of Parkinson's disease (PD) have improved and the population of patients with PD grows and ages. If predictors could be used to identify a sub-population of patients at risk of developing an early PDD then research into its neuropathological basis and treatment could be more effectively targeted to specific individuals. At present the predictors with the most evidence have arisen from longitudinal studies tracking the development of dementia in populations of incident, newly diagnosed patients with PD. Evidence exists for predictors across multiple domains: clinical, biological, neuroimaging and genetic. Some of the most robust of these suggest that PDD may develop as the result of an age and tau dependent, posterior cortically based process driven in some cases by mutations in the gene for glucocerebrosidase (GBA). It is clear, though, that more research needs to be undertaken into finding reliable predictors of PDD. At present the best approach may be to combine a set of predictors already identified in order to provide a basis for understanding why and how it occurs. Through this, new therapeutic strategies may emerge.

BACKGROUND: There is currently little evidence regarding the selection of patients for clinical trials in Parkinson's Disease (PD), especially those involving experimental therapies delivered using invasive techniques. OBJECTIVE: Understanding which patients are recruited will increase awareness of issues regarding parity of access to clinical trials and have an impact on the wider applicability of results, as well as provoking discussion regarding future improvements in the enrolment process. METHODS: TRANSEURO is an open label multi-centre surgical transplant trial which seeks to investigate the feasibility and efficacy of grafts of human foetal ventral mesencephalic tissue in patients with PD. The Cambridge based cohort of TRANSEURO participants (n = 26) was compared with a population representative sample of patients with PD eligible for, but not enrolled in, TRANSEURO (n = 33). Measurements were available in both populations for demographics, neuropsychological tests, tests of motor and non-motor function and quality of life. RESULTS: Patients enrolled in TRANSEURO were younger and had significantly more years of education with higher scores on the revised Addenbrooke's Cognitive Examination. This difference was accounted for by memory, fluency and visuospatial subscores. There were significant differences in the Movement Disorder Society Unified PD Rating Scale scores with better motor function but more motor complications in the enrolled group. Those enrolled were also more likely to be under the care of the principal investigator of the study. CONCLUSIONS: in this trial our population was younger and more educated with higher cognitive scores and better motor function than eligible PD patients not enrolled. This raises interesting questions about the parity of access to clinical trials of this nature amongst patients with PD.