Evaluation of Cerebrospinal Fluid α‐Synuclein Seed Amplification Assay in Progressive Supranuclear Palsy and Corticobasal Syndrome

Background Seed amplification assay (SAA) testing has been developed as a biomarker for the diagnosis of α‐synuclein‐related neurodegenerative disorders. Objective The objective of this study was to assess the rate of α‐synuclein SAA positivity in progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS) and to analyze clinical and pathological features of SAA‐positive and ‐negative cases. Methods A total of 96 cerebrospinal fluid samples from clinically diagnosed PSP (n = 59) and CBS (n = 37) cases were analyzed using α‐synuclein SAA. Results Six of 59 (10.2%) PSP cases were α‐synuclein SAA positive, including one case who was MSA‐type positive. An exploratory analysis showed that PSP cases who were Parkinson's disease–type positive were older and had a shorter disease duration compared with SAA‐negative cases. In contrast, 11 of 37 (29.7%) CBS cases were α‐synuclein SAA positive, including two cases who were MSA‐type positive. Conclusions Our results suggest that α‐synuclein seeds can be detected in PSP and CBS using a cerebrospinal fluid α‐synuclein SAA, and in PSP this may impact on clinical course.