Ictal SPECT Imaging Findings in Parkinson's Disease with Rapid Eye Movement Sleep Behavior Disorder

Background: Rapid eye movement sleep behavior disorder (RBD) is an established prodrome and symptom of synucleinopathies. The pathophysiology of this disorder has been well studied but there is a lack of functional imaging data to illustrate the dysfunction in vivo.

Objectives: We aimed to investigate the functional changes of RBD, by performing ictal REM sleep SPECT, comparing subjects with Parkinson's Disease (PD) and evidence of RBD to subjects with PD and no RBD.

Methods: Participants underwent a targeted clinical assessment, followed by video polysomnography (vPSG). Ictal ^99mTc-HMPAO SPECT was performed by injecting the tracer during vPSG confirmed REM sleep in seven cases (PD with RBD) and five controls (PD without RBD). Voxel-wise, whole brain regional relative perfusion changes between both groups were assessed using statistical parametric mapping.

Results: No difference in relative regional brain perfusion was demonstrated at a family wise error corrected p-value of 0.05 between the case and control groups. At an uncorrected P-value of <0.01, combined with a cluster extent threshold of 300 voxels, four clusters of increased perfusion were identified in the case group compared to the control group. The clusters were seen in the motor, somatosensory association, and prefrontal cortices. The reverse contrast did not show any significant clusters.

Conclusions: Increased perfusion of the motor cortex is in keeping with previous publications and motor phenomena seen in RBD. However, clusters included additional cortical regions. These findings demonstrate RBD as a wider sleep network dysfunction, rather than a manifestation of simple pontomedullary interruption.