Diagnostic performance RT‐QuIC based detection of alpha‐synuclein seeds in a clinical cohort with cognitive impairment.

Background: Lewy Body Dementia (LBD) is the second most common neurodegenerative dementia. To date, no validated biochemical marker is available to support clinical diagnosis. The development of the Real‐Time Quaking‐Induced Conversion (RT‐QuIC) assay for detecting alpha‐synuclein (aSyn) seeds in biological samples can be a sensitive biomarker specific for the diagnosis easily applicable in a clinical setting. We aimed to describe the diagnostic performance of RT‐QuIC aSyn assay in cerebrospinal fluid (CSF) to diagnose LBD in a clinical cohort with cognitive impairment. Method: A cohort of subjects with cognitive impairment (neurodegenerative and non‐neurodegenerative) with available CSF sample at the moment of first evaluation was selected by convenience sample in our database. Subjects had clinical follow‐ups ranging from 6 months to 12 years and current clinical diagnosis according to established consensus criteria. The diagnostic performance of RT‐QuIC aSyn for the diagnosis of LBD were evaluated. Result: The test was evaluated in 155 subjects (age 65 years (SD 11), MMSE 24 (SD 4.5), 56% male) with the following clinical diagnoses: LBD (n = 40), Alzheimer's disease (AD) (n = 73)(all with compatible CSF profile), frontotemporal dementia (FTD) (n = 7), non‐neurodegenerative mild cognitive impairment (MCI) (n = 21), other neurodegenerative diagnoses (n = 12) and healthy controls (n = 2). aSyn was detected in 33/40 (83%) LBD patients, 7/73 (10%) AD, 0/7 FTD patients, 0/21 MCI patients, 0/12 patients with other neurodegenerative diseases and 0/2 healthy controls. Only 3/7 (42%) LBD subjects with a negative RT‐QuIC asyn fulfilled criteria for LBD (established or prodromal) at the moment of first evaluation as compared with 23/33 (69%) of LBD with positive RTQuIC suggesting a more initial disease in the negative group at the moment of CSF sampling. The sensitivity and specificity of the assay were 83% and 94% respectively for the diagnosis of LBD, with a PPV of 83% and a NPV of 94%. Conclusion: Detection of αSyn seeds by RT‐QuIC has a good performance in identifying patients with LBD in a clinical cohort of cognitively impaired subjects. The test also identifies aSyn co‐pathology in a subgroup of subjects diagnosed with AD. [ABSTRACT FROM AUTHOR]