Diagnostic and physiologic RWA cutoffs in Koreans broadly align with Western findings, though discrepancy with earlier Asian cohort data suggests that multinational, multi-ethnic studies are warranted to assess generalizability across Asian populations.
Key Findings
Results
Diagnostic cutoffs for REM sleep without atonia (RWA) with specificity constrained to 1.00 were successfully derived for multiple channel-method combinations in a Korean iRBD cohort.
Cutoffs were derived in 68 patients with iRBD and 46 age- and sex-matched controls.
Combined SM-any and FDS-phasic-3s cutoff was 36.2% (95% CIs, 29.2–42.7%; AUC = 0.98).
Combined SM-any and FDS-phasic-30s cutoff was 21.2% (95% CIs, 7.6–31.9%; AUC = 0.98).
SM-tonic-30s cutoff was 6.5% (95% CIs, 2.8–6.9%; AUC = 0.82).
RAI cutoff was 0.78 (95% CIs, 0.74–0.92; AUC = 0.93) and SM-CRWA% cutoff was 7.1% (95% CIs, 5.5–7.5%; AUC = 0.94).
Results
External evaluation of SM-based diagnostic cutoffs in an independent population-based cohort showed specificities of ≥0.90.
External validation was performed in 68 matched controls from a population-based cohort.
Specificities for diagnostic cutoffs were ≥0.90 in the external cohort.
For optimal cutoffs, specificities fell within the derivation cohort's 95% confidence intervals, with the exception of SM-any-3s.
This indicates reasonable stability of the derived cutoffs across independent samples.
Results
The 95th percentile RWA values in external controls were quantified across multiple scoring methods.
95th percentile values in external controls were: 24.6% for any-3s, 21.9% for any-30s, 9.7% for CRWA%, and 0.91 for RAI.
These values represent physiologic upper-normal limits in the population-based external cohort.
These normative values provide reference ranges for distinguishing pathologic from physiologic RWA levels.
Methods
RWA was quantified using four distinct scoring methods applied to submentalis and bilateral flexor digitorum superficialis EMG channels.
The four methods were: SINBAR (3-second mini-epochs), AASM (30-second epochs), RAI (REM Atonia Index), and CRWA%.
EMG activity was automatically detected using a validated algorithm.
Variables were labeled using a 'channel-event-method' format to systematically compare across approaches.
Both submentalis (SM) and bilateral flexor digitorum superficialis (FDS) muscles were assessed.
Discussion
Korean RWA diagnostic and physiologic cutoffs broadly align with previously reported Western findings, but discrepancies exist with earlier Asian cohort data.
The alignment with Western data suggests that ethnicity alone may not account for major differences in RWA thresholds.
Discrepancy with earlier Asian cohort data indicates that within-Asian variability may be significant.
Authors conclude that multinational, multi-ethnic studies are warranted to assess generalizability across Asian populations.
This is the first study to derive RWA diagnostic cutoffs specifically in a Korean population using a multichannel, multi-method approach.
Results
The combined channel approach (SM plus FDS) achieved the highest AUC values (0.98) for iRBD diagnosis.
Combined SM-any and FDS-phasic-3s yielded AUC = 0.98 with a cutoff of 36.2%.
Combined SM-any and FDS-phasic-30s also yielded AUC = 0.98 with a cutoff of 21.2%.
Single-channel SM-tonic-30s had a lower AUC of 0.82.
These results support the utility of multichannel EMG recording for maximizing diagnostic accuracy.
What This Means
This research suggests that specific thresholds of abnormal muscle activity during REM sleep — a condition called REM sleep without atonia (RWA) — can be reliably measured and used to diagnose isolated REM sleep behavior disorder (iRBD) in Korean patients. iRBD is a sleep disorder where people physically act out their dreams, and it is an important early warning sign for certain neurodegenerative diseases like Parkinson's disease. The researchers used automated analysis of muscle activity from multiple body sites (chin and forearms) and four different scoring methods to determine the exact percentage of REM sleep time that shows abnormal muscle activity, establishing diagnostic cutoffs that correctly identified iRBD patients while avoiding false positives in healthy controls.
The study found that when combining chin and forearm muscle recordings, the diagnostic accuracy was very high (AUC up to 0.98), and these cutoffs held up well when tested in an independent group of healthy individuals from the general population — most showed specificities of 90% or higher. Notably, the thresholds derived in this Korean cohort were broadly similar to those previously reported in Western (primarily European) populations, suggesting that the biological basis of RWA may be consistent across these groups.
However, the Korean findings differed from some earlier data reported in other Asian populations, raising questions about whether RWA thresholds are truly uniform across all Asian ethnic groups. This research suggests that larger multinational studies including diverse Asian populations are needed to confirm whether the same diagnostic cutoffs can be universally applied, which has practical implications for the standardized clinical diagnosis of iRBD worldwide.
Noh T, Byun J, Hong J, Yoon I, Jung K. (2026). Diagnostic cutoffs of REM sleep without atonia for identifying isolated REM sleep behavior disorder in a Korean population.. Sleep medicine. https://doi.org/10.1016/j.sleep.2026.108811