What are the American Academy of Sleep Medicine (AASM) guidelines for diagnosing REM Sleep Without Atonia (RSWA)?

AASM Guidelines for Diagnosing REM Sleep Without Atonia (RSWA)

The American Academy of Sleep Medicine (AASM) defines REM Sleep Without Atonia (RSWA) as the presence of sustained muscle activity (tonic) during REM sleep, measured as epochs with at least 50% of the duration showing EMG chin amplitude greater than the minimum amplitude during NREM sleep, and/or excessive transient muscle activity (phasic) during REM sleep. 1

Diagnostic Criteria for RSWA

• Polysomnography (PSG) is the standard diagnostic test required for the diagnosis of RSWA, as it allows for proper measurement of muscle activity during confirmed REM sleep periods 2
• RSWA is characterized by two main types of abnormal muscle activity during REM sleep:
  • Tonic activity: Sustained muscle tone during REM sleep, defined as epochs with at least 50% of the duration showing EMG chin amplitude greater than the minimum amplitude during NREM sleep 1, 3
  • Phasic activity: Transient muscle activity occurring in brief bursts during REM sleep 1, 3

Quantitative Diagnostic Thresholds

• For 3-second mini-epoch scoring, the diagnostic thresholds for muscle activity are:
  • Submentalis (chin) muscle: 15.5-15.8% for phasic activity and 19.5-21.6% for "any" muscle activity 4, 5
  • Anterior tibialis (leg) muscle: 29.7-30.2% for both phasic and "any" muscle activity 4, 5
  • Combined submentalis/anterior tibialis: 37.9-39.5% for phasic activity and 39.5-43.4% for "any" muscle activity 4, 5
• For tonic muscle activity, diagnostic thresholds range from 0.70% to 1.2% 4, 5
• The REM atonia index (RAI) threshold for submentalis ranges from 0.86 to 0.88 (with lower values indicating more RSWA) 4, 5
• Phasic burst duration thresholds are approximately 0.65-0.72 seconds for submentalis and 0.71-0.79 seconds for anterior tibialis 4, 5, 3

Recent Updates to Diagnostic Thresholds

• Contemporary research (2024) suggests optimized diagnostic cutoffs for:
  • Submentalis "any" activity: 6.5-14.0% (AUC = 92.5%) 3
  • Combined submentalis and flexor digitorum superficialis "any" activity: 15.1-27.4% (AUC = 95.8%) 3
  • Flexor digitorum superficialis RAI: 0.888-0.930 (AUC 92.8%) 3

Important Considerations for Accurate Diagnosis

• Limb movements associated with respiratory events should not be counted as periodic limb movements to avoid misdiagnosis 6
• Respiratory events can trigger limb movements as a physiological response to oxygen desaturation or arousal, which should not be confused with RSWA 6
• Combining phasic burst durations with RSWA muscle activity measurements improves the sensitivity and specificity of diagnosis 4, 5
• RSWA can occur with or without dream-enacting behaviors (REM Sleep Behavior Disorder) 7

Clinical Significance

• RSWA is the polysomnographic hallmark of REM Sleep Behavior Disorder (RBD) 8, 7
• RSWA severity in isolated RBD patients may predict early conversion to neurodegenerative conditions such as Parkinson's disease or dementia with Lewy bodies 7
• In patients with Parkinson's disease, RSWA severity is associated with more severe motor symptoms and disease progression 7

Diagnostic Protocol

• Full-night polysomnography is preferred, though split-night studies can also be used for RSWA assessment 4, 5
• EMG recordings should include at minimum the submentalis (chin) muscle, though additional recordings from limb muscles (anterior tibialis, flexor digitorum superficialis) improve diagnostic accuracy 3
• Both visual scoring methods and automated analyses (such as the REM atonia index) can be used, with combined approaches offering the best diagnostic performance 4, 5, 3