Cutaneous nerve fiber pathology and function in Parkinson's disease and atypical parkinsonism - a cohort study.

There is scientific evidence for ongoing neurodegeneration and alpha-synuclein pathology involving the peripheral nervous system in Parkinson's disease (PD) and multiple system atrophy (MSA). We explored putative disease-mirroring properties of cutaneous nerve fibers in patients with PD (n = 20), MSA (n = 12), four-repeat tauopathies (n = 11), and controls (n = 20). Assessments included clinical rating scales, blood sampling, sudomotor testing, skin punch biopsies from the neck and leg, and 1-year follow-up. Skin alpha-synuclein seeding amplification assay (SAA) and determination of intraepidermal nerve fiber density (IENFD) were performed. Reduced electrochemical skin conductance was evident in MSA, associated with clinical rating scores. Cervical skin SAA (PD vs controls) achieved a 100% sensitivity and 70% specificity for detecting PD. We found no difference in baseline IENFD, nor in 1-year changes, in patients relative to controls. Baseline IENFD, plasma neurofilament light, and SAA kinetics associated with 1-year clinical disease progression in MSA. Skin may harbor promising prognostic properties in MSA.