Insomnia features and patient-reported daytime sleepiness in patients with obstructive sleep apnea

Previous preliminary evidence suggests insomnia features playing a major causative or confounding role in daytime sleepiness in obstructive sleep apnea (OSA) patients. We investigated further this hypothesis in a larger OSA patient cohort. In a cross-sectional study in a tertiary medical center, consecutive patients presenting with suspected OSA, but without other sleepiness-promoting comorbidities, and tested by in-lab polysomnography (PSG) were evaluated prospectively for excessive daytime sleepiness (EDS) using the Epworth Sleepiness Scale (ESS) and for insomnia using the Insomnia Severity Index (ISI) respectively. Two hundred and thirty patients (63 female; average age: 54,1 y) were included in this OSA treatment-naïve cohort. ISI values correlated best (Spearman's rho = 0,29, p < .001) with the total ESS score than any PSG -associated metric did. Especially ISI item 7- (interference of sleep problems with daily functions, r = 0,33, p < .001) and item 2 - (difficulty staying asleep, r = 0,28, p < .001) and to a lesser degree item 4 - (satisfaction with own current sleep patterns, r = 0,23, p = 0,025) scores showed significant correlations. Notably, no single significant correlation was found between ESS score and any PSG-metric at all. In a multiple regression analysis, the ISI item 7 score emerged as the sole significant independent predictor of the ESS score. We conclude that insomnia may significantly impact patient-reported daytime sleepiness in OSA patients. We suggest that assessment of insomnia symptoms and features (e.g. by means of ISI) should always be performed in OSA patients reporting daytime sleepiness. We propose that these preliminary findings should be validated in larger and diverse cohorts of OSA patients.