Polysomnography Interpretation: Mild Obstructive Sleep Apnea with REM-Predominant Pattern
This polysomnography demonstrates mild obstructive sleep apnea (OSA) with a REM-predominant pattern, characterized by an overall AHI of 2.3 (using 4% desaturation criteria) that increases to 9 when using 3% desaturation criteria, with markedly elevated REM-sleep AHI of 7 compared to non-REM AHI <1. 1
OSA Severity Classification
Using the 4% desaturation criterion, the AHI of 2.3 falls below the diagnostic threshold for OSA (AHI <5 = normal), but using the 3% desaturation criterion, the AHI of 9 meets criteria for mild OSA (AHI 5-15). 1
The American Academy of Sleep Medicine defines OSA severity as: Normal (AHI <5), Mild (AHI 5-15), Moderate (AHI 15-30), and Severe (AHI ≥30). 2, 1
The choice of desaturation threshold (3% vs 4%) significantly impacts diagnosis—this patient's classification changes from "normal" to "mild OSA" based on this criterion alone. 1
Key Pathological Findings
REM-Predominant Sleep Apnea Pattern
The REM-sleep AHI of 7 is markedly elevated compared to non-REM AHI <1, indicating REM-predominant OSA—a pattern associated with positional dependency and potentially underestimated severity. 3
REM sleep typically shows more severe respiratory events due to decreased upper airway muscle tone and reduced arousal threshold. 3
Oxygen Desaturation Profile
The lowest oxygen saturation of 84% represents clinically significant desaturation, particularly given the patient spent 71% of the night supine. 4, 5
Multiple oxygen saturation indices correlate with OSA severity: lowest oxygen saturation (LO₂), oxygen desaturation index (ODI), and time spent below 90% saturation (T<90%). 4
The nadir SpO₂ of 84% is inversely correlated with OSA severity and indicates moderate hypoxemic stress during respiratory events. 3, 4
Sleep Architecture Abnormalities
The shortened REM latency of 44 minutes (normal >90 minutes) suggests sleep fragmentation or underlying sleep debt. 2
Sleep efficiency of 90% is within normal limits, but frequent awakenings up to 14 minutes duration indicate sleep fragmentation despite adequate total sleep time. 2
Sleep latency of 1 minute is abnormally short, suggesting either severe sleepiness or sleep deprivation. 2
Positional Dependency
71% supine sleep position is clinically significant—supine-predominant OSA typically shows 2-3 fold higher AHI in supine versus non-supine positions. 2
The combination of REM-predominant and likely positional OSA suggests this patient's true OSA severity may be underestimated if they sleep non-supine at home. 2
Clinical Implications and Treatment Considerations
Diagnostic Certainty
This patient meets criteria for mild OSA using 3% desaturation criteria (AHI 9), which is the more sensitive and clinically relevant threshold for detecting respiratory events. 1, 6
The REM AHI of 7 alone would classify as mild OSA even using 4% criteria, supporting the diagnosis. 1
Treatment Recommendations
CPAP therapy is indicated when AHI ≥5 with documented symptoms (excessive daytime sleepiness, impaired cognition, mood disorders, insomnia) or cardiovascular comorbidities. 7
For Medicare coverage, CPAP requires either AHI ≥15, or AHI ≥5 with symptoms—this patient qualifies if symptomatic. 7
Positional therapy should be considered given 71% supine sleep and likely positional component. 2
Common Pitfalls to Avoid
Do not dismiss this study as "normal" based solely on the 4% desaturation AHI of 2.3—the 3% criterion AHI of 9 and REM AHI of 7 indicate clinically significant disease. 1, 6
The REM-predominant pattern means this patient experiences significant respiratory disturbance during the most restorative sleep stage, which can cause disproportionate symptoms despite "mild" overall AHI. 3
Supine-predominant OSA may be more severe than captured if the patient typically sleeps in other positions at home. 2
The combination of short sleep latency (1 minute) and short REM latency (44 minutes) suggests significant sleep debt or fragmentation that warrants clinical correlation. 2
Additional Evaluation Needed
Clinical correlation with symptoms (Epworth Sleepiness Scale, witnessed apneas, morning headaches, cardiovascular comorbidities) is essential to determine treatment necessity. 7
Consider repeat study if symptoms are severe but AHI appears mild, as night-to-night variability and positional factors may underestimate true severity. 2
Evaluate for cardiovascular comorbidities (hypertension, arrhythmias, coronary disease) which lower the treatment threshold. 7