Idiopathic rapid eye movement sleep behaviour disorder is characterized by nocturnal violence,
increased muscle tone during rapid eye movement sleep and the lack of any other neurological disease. However, idiopathic rapid eye movement sleep behaviour disorder can precede
parkinsonism and
dementia by several years. Using 3 T magnetic resonance imaging and
neuromelanin-sensitive sequences, we previously found that the signal intensity was reduced in the locus coeruleus/subcoeruleus area of patients with
Parkinson's disease and rapid eye movement sleep behaviour disorder. Here, we studied the integrity of the locus coeruleus/subcoeruleus complex with
neuromelanin-sensitive imaging in 21 patients with idiopathic rapid eye movement sleep behaviour disorder and compared the results with those from 21 age- and gender-matched healthy volunteers. All subjects underwent a clinical examination, motor, cognitive, autonomous, psychological, olfactory and colour vision tests, and rapid eye movement sleep characterization using video-polysomnography and 3 T magnetic resonance imaging. The patients more frequently had preclinical markers of
alpha-synucleinopathies, including
constipation, olfactory deficits,
orthostatic hypotension, and subtle motor impairment. Using
neuromelanin-sensitive imaging, reduced signal intensity was identified in the locus coeruleus/subcoeruleus complex of the patients with idiopathic rapid eye movement sleep behaviour. The mean sensitivity of the visual analyses of the signal performed by neuroradiologists who were blind to the clinical diagnoses was 82.5%, and the specificity was 81% for the identification of idiopathic rapid eye movement sleep behaviour. The results confirm that this complex is affected in idiopathic rapid eye movement sleep behaviour (to the same degree as it is affected in
Parkinson's disease).
Neuromelanin-sensitive imaging provides an early marker of non-dopaminergic
alpha-synucleinopathy that can be detected on an individual basis.