Rapid-eye-movement-specific Sleep-disordered Breathing: a Possible Cause of Excessive Daytime Sleepiness

Some patients referred for polysomnography with complaints of excessive daytime sleepiness (EDS) and clinically suspected obstructive sleep apnea (OSA) have a respiratory disturbance index (RDI) < 10. Many would consider these patients not to have OSA. We reviewed 34 such patients to determine whether respiratory disturbances confined primarily to rapid eye movement (REM) sleep correlated with an objective criterion for EDS: a mean sleep latency (MSL) < 10 min. REM-specific events were quantified with indices calculated for REM sleep alone. Univariate linear regression showed that a REM-specific respiratory disturbance index (REM-RDI) and the transient arousal index (TAI) computed for REM sleep (REM-TAI) were associated with a low MSL (R2 = -0.35, p = 0.001; and R2 = -0.27, p = 0.01, respectively). In our subjectively sleepy patients with an overall RDI < 10, a REM-RDI > or = 15 had the highest predictive accuracy (82%) for an MSL < 10 min. Seventeen of the 34 study patients had a REM-RDI > or = 15. Their mean MSL was 8.3 +/- 0.8 min. We conclude that within a group of patients with daytime sleepiness, suspected OSA, and a normal RDI, there may be a subset who have clinically significant REM-specific sleep-disordered breathing.