Clinical and polysomnographic characteristics of patients with excessive daytime sleepiness

Background and Objective Excessive daytime sleepiness (EDS) is a common symptom of many sleep disorders. EDS is the result of disturbed sleep or the sleep-waking process. The measurement of the degree of EDS is important for diagnosis and for its correlation with the severity of sleep disorders. We aimed to compare the characteristics of sleep disorders which were related to EDS and to investigate whether the Epworth Sleepiness Scale (ESS) and multiple sleep latency test (MSLT) were correlated with the polysomnographic parameters. Methods 387 patients with EDS who completed both polysomnography (PSG) and MSLT were included. The severity of EDS was evaluated using ESS. Comparison of demographic, PSG, and MSLT results according to the final diagnosis and obstructive sleep apnea (OSA) subgroups categorized by the Apnea-Hypopnea Index. Results The ESS score did not differ between the groups, except for narcolepsy type 1 and delayed sleep phase disorder (p = 0.026). While the ESS score showed weak correlation with some PSG parameters, the mean sleep latency (mSL) of MSLT showed a significant and stronger correlation with PSG parameters. The mSL was significantly shorter in patients with severe OSA (4.6 ± 3.0, p < 0.001) while the ESS did not show any difference among the different severities of OSA (p = 0.754). Parameters which reflect OSA severity showed significant correlations with mSL. Conclusions ESS is insufficient for reflecting differences in the types and severities of sleep disorders, so the objective parameters of PSG and MSLT are necessary for more precise diagnosis. There was significant but weak correlation with mSL in the case of ESS ≤ 10, indicating that ESS was a poor screening tool but could be a convenient tool for follow-up study, rather than repeated MSLT.