Objective:

To determine whether autonomic reflect testing can predict phenoconversion in individuals with isolated REM sleep behavior disorder (iRBD).

Background:

Autonomic dysfunction is common across alpha (α)-synucleinopathy subtypes,
including iRBD, a prodromal state of the α-synucleinopathies. However, the presence and distribution of autonomic dysfunction as a risk factor for phenoconversion in iRBD remains unclear.

Design/Methods:

We performed ART on 45 individuals with iRBD and followed them yearly for an average of 4.6 yrs., during which 6 individuals phenoconverted. We evaluated the ability of individual ART components (sympathetic cholinergic, cardiovagal, sympathetic adrenergic) to predict phenoconversion using predictive models, both alone and combined with measures of olfaction, cognition, motor function, and skin biopsy assessment of dermal α-synuclein. Six individuals had follow-up ART.  

Results:

87% of iRBD participants had an abnormal baseline ART, and 100% had an abnormal follow-up ART. A combination of cardiovagal function (abnormal heart rate variability with deep breathing) and MDS-UPDRS III score best predicted phenoconversion (AUC = 0.74).

Conclusions:

Autonomic dysfunction is common in iRBD. Cardiovagal dysfunction was most commonly affected and most predictive of phenoconversion, especially if combined with motor examination.