Two-step detection of Lewy body pathology via smell-function testing and CSF α-synuclein seed amplification.

Cerebrospinal fluid (CSF) α-synuclein (α-syn) seed amplification assays (SAAs) can detect Lewy body pathology (LBP) with high accuracy but are invasive and costly. To address these challenges, this study evaluated a two-step workflow combining prescreening via smell-function testing with confirmatory CSF α-syn SAA testing only in individuals with reduced smell, for predicting postmortem LBP status. Among 358 autopsied participants, the two-step workflow predicted brain LBP with high accuracy overall (94%), and within clinical subgroups (clinical parkinsonism=95%; clinical Alzheimer's disease [AD]=94%; clinically unimpaired [CU]=93%). It reduced the need for confirmatory CSF testing by 43% overall (23% clinical parkinsonism; 35% clinical AD; 80% CU). In an independent in vivo cohort (N=1209), the workflow predicted CSF α-syn SAA status with 79% accuracy and reduced CSF testing by 26%. This approach may reduce invasive CSF testing, alleviating patient burden and lowering healthcare costs.