Supporting meaningful contributions of people affected by Parkinson's throughout the research process: Key considerations for inclusive patient and public involvement across the globe

Patient and public involvement (PPI), defined as research undertaken with people affected by a condition as partners rather than participants, is increasingly recognized as a marker of high-quality research and is now encouraged or required by many funders. Research agendas and practices need to reflect the realities of people living with Parkinson's Disease (PD) ensuring research addresses the priorities of those affected.

This narrative review examines the role of PPI across the research cycle, including priority setting, commissioning, study design, delivery, dissemination, implementation, and evaluation. We provide guidance and practical examples of how meaningful PPI can be achieved in PD research. The review explains how perspectives of lived experience can improve the relevance, feasibility, accessibility, and highlight its impact on PD research. We discuss practical considerations for embedding meaningful PPI, including project governance structures, dedicated staffing, remuneration, flexibility in conduct, and how to embed the perspectives of under-served PD communities in PPI. Finally, we consider challenges and opportunities for PPI in low- and middle-income countries, where underdiagnosis, stigma, health literacy barriers, and structural inequities require culturally responsive and community-led approaches.

Involving people affected by Parkinson's as equal partners in research has the potential to improve individual studies and to reshape the wider PD research agenda to be more inclusive, representative, and responsive to the priorities of those most affected.

To realise this potential, we must make a collective commitment to treat PPI as a requirement, provide funding and infrastructure support for implementation, and share experiences.