Critical appraisal of brain pathology staging related to presymptomatic and symptomatic cases of sporadic Parkinson's disease.

Clinical Parkinson's disease (PD) is a well-characterised syndrome that benefits significantly from dopamine replacement therapies. A staging procedure for sporadic PD pathology was developed by Braak et al. assuming that the abnormal deposition of alpha-synuclein indicates the intracellular process responsible for clinical PD. This paradigm has merit in corralling patients with similar cellular mechanisms together and determining the potential sequence of events that may herald the clinical syndrome. Progressive pathological stages were identified--1) preclinical (stages 1-2), 2) early (stages 3-4, 35% with clinical PD) and 3) late (stages 5-6, 86% with clinical PD). However, preclinical versus early versus late-stage cases should on average be progressively older at the time of sampling, a feature not observed in the cohort analysed. In this cohort preclinical cases would have developed extremely late-onset PD compared with the other types of cases analysed. While the staging scheme is a valuable concept, further development is required.