Is there a need to redefine Parkinson's disease?

Parkinson's disease (PD) is classically defined by its cardinal motor features and current clinical diagnostic criteria require the presence of bradykinesia and at least one additional motor symptom out of tremor, rigidity or postural instability. However, converging evidence from clinical, neuropathological, imaging and genetic research suggests initiation of PD-specific pathology prior to appearance of classical motor signs. This is of particular relevance in relation to the development of disease-modifying or neuroprotective therapies which would require intervention at the earliest stages of disease. A key challenge in PD research, therefore, is to better characterize markers for the 'preclinical' stages of the illness. Development of PD criteria by combining such markers allowing for an early diagnosis and intervention could pave the way for the design and implementation of future disease modification trials.