Systematic video-analysis of motor events during REM sleep in idiopathic REM sleep behavior disorder, follow-up and DAT-SPECT

Abnormal motor manifestations in REM sleep are the most visible feature of idiopathic REM sleep behavior disorder (iRBD), which precedes the overt alpha-synucleinopathy. The aim of this study was to perform a systematic visual analysis of the motor events (ME) captured during video-polysomnography, and clarify their relation to the disease severity. Thirty-four iRBD patients (5 women, 29 men; age 67.7 ± 7.2) with a mean follow-up duration 2.9 ± 1.1 years. and 33 controls (10 women, 23 men; age 61.5 ± 8.2) were examined. The ME captured during REM sleep were classified into four categories, previously defined by Frauscher et al. according to clinical severity: minor/simple jerks, major, complex and violent. An average frequency of 110.8 ± 75.2 ME per hour were identified in iRBD, 7.5 ± 11.6 in the controls (p < 0.001). Of these ME, 68.4% were classified as minor/simple jerks, 9.3% as major, 21.7% as complex and 0.7% as violent. The ME frequency was negatively associated with tracer binding on dopamine transporter single-photon emission computed tomography (DAT-SPECT); the association was stronger for caudate nucleus compared to putamen. During follow-up seven patients (24.1%) phenoconverted, yielding a yearly phenoconversion rate 8.3%. Violent ME were associated with increased hazard ratio for phenoconversion in frequency (p = 0.012) and total duration (p = 0.007). Patients with higher amounts of violent ME had a greater risk of phenoconversion; therefore, their role as a predictor should be considered. Additionally, ME were associated with nigrostriatal degeneration, according to DAT-SPECT. These findings indicate that the degree of the clinical severity of motor manifestations in iRBD reflects the severity of the disease.