Objective: To describe the frequencies of neurodegenerative biomarker abnormalities in the adult Mayo Clinic iRBD prospective registry cohort.

Background: The majority of patients with idiopathic REM sleep behavior disorder (iRBD) are thought to have prodromal synucleinopathy. Many iRBD patients have neurodegenerative biomarker abnormalitiessuch as olfactory, orthostatic blood pressure, cognitive, or motor function impairments. We sought to describe the frequencies of neurodegenerative biomarker abnormalities in the adult Mayo Clinic iRBD prospective registry cohort.

Methods: We included adults diagnosed with iRBD by ICSD-3 criteria, and excluded symptomatic RBD patients (i.e., diagnosis of mild cognitive impairment, dementia with Lewy bodies, Parkinson disease, or multiple system atrophy). We considered clinical neurodegenerative biomarker measures as abnormal when subjects met age- and sex-defined cut-offs for the brief Smell Identification Test (BSIT) and neurocognitive assessments [Montreal Cognitive Assessment (MOCA), “Kokmen” Short Test of Mental Status (STMS)], King-Devick Test (KDT), orthostatic systolic blood pressure (SBP) drop >10 mm Hg, or timed up and go (TUG) speed > 7.5 seconds.

Results: Thirty-eight iRBD subjects participated. Mean age was 65.4 (range 21 – 84) years, and 12 (31%) were women. Duration of dream enactment symptoms was 11+/-16 years. Eighteen (47%) were receiving antidepressant medications. Mean (range) measure scores were: BSIT 8.8 (4-12) correct, MOCA 26.2 (20-30), STMS 34.3 (30-38), KD 60.2 (39-125.6) seconds, SBP drop 14.64 (1-49), and TUG 8.5 (5.3-13.8) seconds. The number (%) with abnormal biomarker measures were: BSIT 6 (16%), MoCA 6 (16%), STMS 0%, KD 12 (32%), SBP drop 15 (41%), and TUG 11 (31%). Overall, 31 (82%) had one or more clinical neurodegenerative biomarker abnormalities at baseline, and 20 (52%) had two or more at baseline.  Antidepressant medication was not associated with abnormality on any of the measures.

Conclusions: Over 80% of iRBD patients in this cohort had at least one neurodegenerative biomarker abnormality present, supporting the hypothesis that iRBD is a prodromal synucleinopathy. Further longitudinal analyses of this cohort compared to matched control subjects are planned.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/neurodegenerative-biomarker-abnormality-frequency-in-idiopathic-rem-sleep-behavior-disorder/