Cerebrospinal-fluid biomarkers for predicting phenoconversion in patients with isolated rapid-eye movement sleep behavior disorder.

Study objectives: Patients with isolated rapid-eye-movement sleep behavior disorder (iRBD) have an increased risk of developing neurodegenerative diseases. This study assessed cerebrospinal-fluid (CSF) biomarkers of neurodegeneration and blood-brain barrier (BBB) alteration in patients with iRBD compared to controls and ascertain whether these biomarkers may predict phenoconversion to alpha-synucleinopathies (Parkinson's Disease (PD), Dementia with Lewy bodies (DLB), Multiple System Atrophy (MSA)).

Methods: Patients and controls underwent between 2012 and 2016 a neurological assessment, a lumbar puncture for CSF biomarker analysis (β-amyloid42 - Aβ42; total-tau, and phosphorylated tau), and BBB alteration (CSF/serum albumin ratio). All patients with iRBD were followed until 2021 and then classified into patients who converted to alpha-synucleinopathies (iRBD converters, cRBD) or not (iRBD non-converters, ncRBD).

Results: Thirty-four patients with iRBD (mean age 67.12 ± 8.14) and 33 controls (mean age 64.97 ± 8.91) were included. At follow-up (7.63 ± 3.40 years), eight patients were ncRBD and 33 patients were cRBD: eleven converted to PD, 10 to DLB, and two to MSA. Patients with iRBD showed lower CSF Aβ42 levels and higher CSF/serum albumin ratio than controls. Cox regression analysis showed that the phenoconversion rate increases with higher motor impairment (hazard ratio [HR] = 1.23, p = 0.032). CSF Aβ42 levels predicted phenoconversion to DLB (HR = 0.67, p = 0.038) and BBB alteration predicted phenoconversion to PD (HR = 1.20, p = 0.038).

Discussion: This study showed that low CSF Aβ42 levels and high BBB alteration may predict the phenoconversion to DLB and PD in patients with iRBD, respectively. These findings highlight the possibility to discriminate phenoconversion in iRBD patients through CSF biomarkers; however, further studies are needed.