Biologic Definition of Parkinson Disease: A Pivotal Role for Molecular Imaging

I]MIBG scintigraphy-provide objective in vivo measures of neurodegeneration that complement α-synuclein seed amplification assays and genetic stratification. In addition, we review the current state of α-synuclein PET tracer development and critically evaluate its potential to enable direct visualization of disease-defining pathology in vivo. We highlight the growing importance of biomarker-driven classification systems for patient stratification and the design of trials of disease-modifying therapies in PD. At the same time, we address key scientific, methodologic, and ethical challenges associated with implementing biologically grounded disease definitions. Together, these developments position molecular imaging as a cornerstone of future precision medicine approaches in PD.