Prevalence of objective excessive daytime sleepiness in a cohort of patients with mild obstructive sleep apnea

Study objectives Obstructive sleep apnea (OSA) is common, yet the relationship between mild OSA and excessive daytime sleepiness (EDS) is unclear. Our objective was to determine the prevalence of objective EDS in a population with mild OSA using the mean sleep latency (MSL) from the multiple sleep latency test (MSLT). Methods We retrospectively analyzed 1205 consecutive patients who underwent a polysomnography and a following day MSLT at a single sleep center. Adult patients who met criteria for mild OSA with an apnea-hypopnea index of 5 to <15 events/h were identified, and the percentage of patients with a MSL <= 8 min was determined. Sleep study and demographic variables were examined to evaluate predictors of objective EDS. Results Of 155 patients with mild OSA, objective EDS was found in 36% (56/155) with an average MSL of 5.6 +/- 2.1 min in the objectively sleepy patients. Objectively sleepy patients with mild OSA had greater total sleep time (411.6 +/- 48.9 vs. 384.5 +/- 61.7 min, p = 0.004), increased sleep efficiency (84.9 +/- 9.7 vs. 79.7 +/- 12.7%, p = 0.01), and decreased wake after sleep onset time (53.0 +/- 36.9 vs. 67.4 +/- 46.1 min, p = 0.04) compared to patients with mild OSA but without objective EDS, with total sleep time being an independent predictor of MSL (p = 0.006). The Epworth Sleepiness Scale (ESS) weakly correlated with objective EDS (rho = - 0.169, p = 0.03). Conclusions There is a large subgroup of patients with mild OSA patients who have objective sleepiness. This may represent an ideal subgroup to target for future studies examining the effect of treatment in mild OSA. Additionally, the ESS was a poor predictor of this subgroup with mild OSA and objective EDS.