α‐Synuclein real‐time quaking‐induced conversion in the cerebrospinal fluid of uncertain cases of parkinsonism

A reliable biomarker is needed for accurate and early differentiation between Parkinson disease and the various forms of atypical parkinsonism. We used a novel real‐time quaking‐induced conversion (RT‐QuIC) assay to detect α‐synuclein (α‐syn) aggregates in cerebrospinal fluid (CSF) of 118 patients with parkinsonism of uncertain clinical etiology and 52 controls. Diagnostic accuracy to distinguish α‐synucleinopathies from non–α‐synucleinopathies and controls was 84% (sensitivity = 75%, specificity = 94%, area under the curve = 0.84, 95% confidence interval = 0.78–0.91, p < 0.0001, positive predictive value = 93%). CSF α‐syn RT‐QuIC could be a useful diagnostic tool to help clinicians differentiate α‐synucleinopathies from other forms of parkinsonism when the clinical picture is uncertain. Ann Neurol 2019;85:777–781