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BackgroundThe second consensus criteria for the diagnosis of multiple system atrophy (MSA) are widely recognized as the reference standard for clinical research, but lack sensitivity to diagnose the disease at early stages.ObjectiveTo develop novel Movement Disorder Society (MDS) criteria for MSA diagnosis using an evidence-based and consensus-based methodology.MethodsWe identified shortcomings of the second consensus criteria for MSA diagnosis and conducted a systematic literature review to answer predefined questions on clinical presentation and diagnostic tools relevant for MSA diagnosis. The criteria were developed and later optimized using two Delphi rounds within the MSA Criteria Revision Task Force, a survey for MDS membership, and a virtual Consensus Conference.ResultsThe criteria for neuropathologically established MSA remain unchanged. For a clinical MSA diagnosis a new category of clinically established MSA is introduced, aiming for maximum specificity with acceptable sensitivity. A category of clinically probable MSA is defined to enhance sensitivity while maintaining specificity. A research category of possible prodromal MSA is designed to capture patients in the earliest stages when symptoms and signs are present, but do not meet the threshold for clinically established or clinically probable MSA. Brain magnetic resonance imaging markers suggestive of MSA are required for the diagnosis of clinically established MSA. The number of research biomarkers that support all clinical diagnostic categories will likely grow.ConclusionsThis set of MDS MSA diagnostic criteria aims at improving the diagnostic accuracy, particularly in early disease stages. It requires validation in a prospective clinical and a clinicopathological study. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Immune changes occur in all neurodegenerative conditions, but there are significant differences between diseases. For Parkinson's disease (PD), the immune system involvement is still being identified with considerable promise for therapeutic targeting. Post-mortem analyses of PD patient brains and pre-clinical cell and rodent models of PD identify increased inflammation in the brain and an elevation in central and peripheral pro-inflammatory cytokines. The cells involved include activated microglia surrounding degenerating neurons, currently thought to be neuroprotective in early disease stages but detrimental at later stages. Very different astrocytic reactions are found in the PD brain compared to other neurodegenerative conditions, with a loss of normal astrocyte functions contributing to a neurotoxic or dysfunctional phenotype (rather than classical astrogliosis found in all other neurodegenerative conditions). Astrocytes in PD are also actively involved in clearing α-synuclein away from vulnerable neurons, but the eventual accumulation of α-synuclein in their cytoplasm promotes a pro-inflammatory response and contributes to their dysfunctional phenotype and the spreading of PD pathology. Infiltration of peripheral immune cells also occurs in the PD brain, particularly T cells and monocytes. Both CD4 and CD8 T cells occur in regions of cell loss, with cytotoxic CD8 T cells occurring in the earliest stages and CD4 T helper cells occurring with disease progression. Current evidence points towards infiltrating monocytes as also playing a role in neuron death. Further characterisation of the successive molecular changes in both the resident and peripheral immune cells invading the PD brain will provide targets for disease modification.

We are at a critical juncture in our knowledge of the etiology and pathogenesis of Parkinson disease (PD). It is clear that PD is not a single entity simply resulting from a dopaminergic deficit; rather it is most likely caused by a combination of genetic and environmental factors. Although there is extensive new information on the etiology and pathogenesis of PD, which may advance its treatment, new syntheses of this information are needed. The second part of this two-part, state-of-the-art review by leaders in PD research critically examines the research field to identify areas for which new knowledge and ideas might be helpful for treatment purposes. Topics reviewed in Part II are genetics, animal models, and oxidative stress.