Magnetic resonance imaging in rapid eye movement sleep behavior disorder: Diffusion tensor imaging and voxel-based morphometry

While rapid eye movement (REM) sleep behaviour disorder (RBD) in animals has been associated with stuctural brain stem lesions since the very beginning of RBD research, human brain imaging of RBD did not reveal specific results at first. It was later that single cases of symptomatic RBD due to inflammatory, neoplastic or ischemic lesions were described. Only recently, systematic voxel-based morphometry (VBM) and diffusion tensor imaging (DTI) studies for RBD have been performed. The SINBAR Sleep Innsbruck Barcelona Group investigated 26 idiopathic RBD (iRBD) patients and 14 age-matched controls with both statistical parametric mapping (SPM) and DTI. Substantial decreases of fractional anisotropy in midbrain tegmentum and rostral pons were found, and mean diffusivity was increased in midbrain and pontine reticular formation. In addition VBM revealed an increase of gray matter densities in both hippocampi of iRBD patients. The Marburg group performed DTI in 12 iRBD and 12 controls and reported microstructural changes in the brainstem, substantia nigra, olfactory region, left temporal lobe, coronal radiata and the right visual stream. A recent study performed VBM in 20 iRBD and compared the findings to 18 age-matched controls. This study found significant gray matter volume reduction in the anterior lobes of the cerebellum, the pontine tegmentum and the left parahippocampal gyrus. In summary, the areas highlighted from these studies are in line with areas regulating features of REM sleep, and in part with evolving synucleinopathies.