α-Synuclein seed amplification assay in Lewy body dementia versus Alzheimer's disease.

INTRODUCTION

Differentiating dementia with Lewy bodies (DLB) from Alzheimer's disease (AD) is challenging. Seed amplification assay (SAA) is sensitive for the detection of misfolded α-synuclein.

METHODS

Patients with DLB (N = 31) and AD (N = 25) were recruited and evaluated. Misfolded α-synuclein was assessed in cerebrospinal fluid (CSF), skin, urine, and olfactory mucosa using SAA.

RESULTS

The accuracy of α-synuclein-SAA for DLB was 87% (95% confidence interval [CI]: 77% to 98%) in CSF, 85% (95% CI: 75% to 98%) in skin, 58% (95% CI: 47% to 69%) in olfactory mucosa, and 59% (95% CI: 51% to 66%) in urine. The core symptoms - fluctuations, REM sleep behavior disorder, and parkinsonism - had accuracies for SAA positivity of ≥79%. Notably, 95% of SAA-positive patients also had hyposmia.

DISCUSSION: These findings support the use of CSF and skin α-synuclein-SAAs as diagnostic tools for DLB, with strong associations between SAA and clinical phenotype. In particular, intact olfactory function is associated with a lower risk of SAA positivity.

HIGHLIGHTS: CSF and skin biopsies show high diagnostic accuracy for α-synuclein, demonstrating good concordance.Strong correlations exist between core symptoms of DLB and pathological α-synuclein.A very high sensitivity of hyposmia for pathological α-synuclein is observed.A novel proof-of-concept is offered for the potential detection of pathological α-synuclein in urine, marking the first such comparative analysis between patients with DLB and AD.