Objective: Do motor abnormalities in iRBD patients relate to volume and shape abnormalities in subcortical structures involved in cortico-subcortical circuitry?

Background: Idiopathic rapid eye movement sleep behavior disorder (iRBD) is considered as a risk factor for the development of Parkinson’s disease. Structural brain abnormalities preceding onset of motor signs in Parkinson’s disease remain poorly understood and iRBD offers one way to better understand preclinical Parkinson’s disease. In iRBD, both volume and cortical thickness abnormalities are found. Another technique, vertex-based shape analysis, allows for quantification of surface differences and overcomes some limitations of voxel-based measures. No study has yet studied shape of subcortical structures in relation to motor abnormalities in iRBD patients.

Methods: Forty-one patients with iRBD and 41 controls underwent MRI examination. Voxel-based morphometry (VBM) was used to investigate local gray matter volume. Subcortical structures (i.e., putamen, caudate nucleus, globus pallidus, and thalamus) were studied for global volume and shape. Patients with iRBD underwent several motor tasks including the alternate finger tapping test, the Purdue Pegboard test, and the Timed Up and Go test. The UPDRS-III was conducted to assess severity of motor symptoms.

Results: Shape in the left caudate nucleus correlated significantly with alternate finger tapping test using both hands (r=0.50, cluster size: 552 vertices), the left hand only on the medial surface (r=0.48, size: 569 vertices) and the lateral surface (r=-0.47, size: 211 vertices), and the right hand (r=0.46, size: 154 vertices). Significant relationships were also obtained between the alternate finger tapping test score for both hands and normalized volume of the left caudate nucleus (r=0.31) and between UPDRS-III scores and the left putamen (r=-0.33). UPDRS-III scores on the left side also correlated with a cluster of gray matter volume in the cerebellopontine angle (r=0.56, size: 47 voxels).

Conclusions: In summary, patients with iRBD present with shape and global volume abnormalities that relate to motor abnormalities. The alternate finger tapping test, as the only motor task that correlated significantly with anatomical measures, was associated with both shape and volume. Abnormal motor signs were also associated to volume in a region that encompasses the dorsal IX/X motor nucleus.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/shape-and-volume-abnormalities-relate-to-motor-abilities-in-idiopathic-rapid-eye-movement-sleep-behavior-disorder/