Autonomic impairment in REM sleep behavior disorder: a potential biomarker of phenoconversion?

Excerpt

Since the seminal description in 1986 by Schenck and Mahowald [9], rapid eye movement sleep behavior disorder (RBD) has been well established as one of the earliest and specific prodromal signs of impending α-synucleinopathy-induced neurodegeneration. Idiopathic—or the more accurate contemporary term “isolated”—RBD (iRBD) is a diagnosis implying the absence of other signs or symptoms of clinically manifest α-synucleinopathy [e.g. Parkinson’s disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy (MSA), or pure autonomic failure (PAF)]. Several longitudinal studies have now demonstrated that patients with iRBD have a very high risk  of developing one of these disorders within their lifetime, with an overall phenoconversion rate of close to 90%, or 6–10% per year from the time of the iRBD diagnosis [3, 7, 8]. Like RBD, autonomic impairment is a prodromal manifestation of the α-synucleinopathies, and like RBD can occur decades prior to phenoconversion [2, 10]. Indeed, many patients with RBD have findings consistent with PAF [6] and, conversely, patients with PAF frequently have RBD [4]. The co-segregation of RBD and autonomic dysfunction provides rationale for the evaluation of autonomic impairment as a potential biomarker in patients with iRBD, however few studies on this topic have been reported [1]. …