REM-Related Obstructive Sleep Apnea (REM OSA): Definition and Clinical Significance
REM OSA is defined as obstructive respiratory events occurring predominantly or exclusively during REM sleep, characterized by an apnea-hypopnea index (AHI) ≥5 per hour with a ratio of REM-AHI to NREM-AHI >2 and NREM-AHI <15 per hour. 1, 2, 3
Key Characteristics of REM OSA
Pathophysiology
- Occurs when the upper airway is most prone to collapse due to REM sleep atonia 1
- Respiratory events during REM sleep are typically:
Epidemiology
- Higher prevalence in women than men 1, 3
- More common in patients under 60 years of age 3
- Usually occurs in the context of mild-to-moderate overall OSA severity 1
- Prevalence estimated at 21.6% of OSA patients in some populations 3
Diagnostic Criteria
- Requires polysomnography (PSG) to diagnose, as it's necessary to differentiate REM from NREM sleep 4
- According to the International Classification of Sleep Disorders (ICSD-3), OSA diagnosis requires:
- PSG-determined obstructive RDI ≥5 events/hour with typical OSA symptoms, or
- Obstructive RDI ≥15 events/hour even without symptoms 4
- For REM OSA specifically, the ratio of REM-AHI to NREM-AHI should be >2 3
Clinical Significance and Health Implications
Cardiovascular Impact
- Associated with systemic hypertension independently of overall AHI 1
- May increase cardiometabolic risk 1
- Higher prevalence in patients with diabetes mellitus 5
- Associated with reduced daytime cerebral blood flow in the ventromedial prefrontal cortex and insula 6
Neurological Impact
- Causes excessive daytime sleepiness similar to non-stage-dependent OSA 1
- Affects brain health even in milder OSA cases 6
- Reduced daytime regional cerebral blood flow observed even in patients with AHI <15 6
Treatment Considerations
PAP Therapy Challenges
- CPAP treatment for REM OSA should be longer than the standard 4 hours considered as good compliance 1
- This is because REM sleep occurs predominantly during the second half of the night 1
- Patients with REM OSA often show poor adherence to CPAP therapy 1
Treatment Approach
- Treatment decisions should consider the overall AHI as well as REM-specific AHI 2
- For patients with comorbid insomnia and OSA, a combined approach using cognitive behavioral therapy for insomnia (CBT-I) followed by PAP therapy is recommended 7
Diagnostic Pitfalls to Avoid
- Failing to acquire sufficient REM sleep during diagnostic testing (at least 30 minutes recommended) 5
- Not distinguishing between REM and NREM events when interpreting sleep studies 2
- Overlooking REM OSA in patients with mild overall AHI but significant REM-specific events 2
- Not considering REM OSA in female patients or those with diabetes mellitus, who have higher prevalence 5, 3
REM OSA represents a distinct clinical entity with potentially significant health implications even when the overall AHI suggests mild disease. Proper diagnosis requires careful attention to sleep stage-specific respiratory events during polysomnography, and treatment may need to be tailored to ensure adequate coverage during REM sleep periods.