Impact of Depression on Cognitive Function and Phenoconversion to Neurodegenerative Diseases in Patients With Isolated REM Sleep Behavior Disorder

Background: This study was aimed at analyzing cognitive function and quantitative electroencephalogram (qEEG) in patients with isolated REM sleep behavior disorder (iRBD) based on the presence of depression and at evaluating the impact of depression on phenoconversion to neurodegenerative diseases.Methods: Individuals diagnosed with iRBD via polysomnography were included. Based on the presence of depression, patients were categorized into two groups. Neuropsychological tests and qEEG were conducted following the diagnosis of iRBD, and outcomes were compared between the two groups. Patients were regularly followed to monitor their phenoconversion status. Cox regression analysis was performed to assess the hazard ratio associated with depression.Results: Ninety iRBD patients (70% males) were included, with a median age of 66.3 years. Depression was identified in 26 (28.9%) of these patients. The depressed group showed significantly poorer performance only in color reading subtest of Stroop (p=0.029) compared to the nondepressed group, showing reduced processing speed. In qEEG, relative gamma power (p=0.034) and high gamma power (p=0.020) in the parietal region were significantly higher in the depressed group than in the nondepressed group. Depression was associated with a hazard ratio of 3.32 for the risk of phenoconversion to neurodegenerative diseases in iRBD patients (p=0.011).Conclusion: Depressive symptoms in iRBD patients should be closely monitored as they could aggravate cognitive dysfunction and increase the risk of phenoconversion to neurodegenerative diseases.