Daytime sleepiness and disturbed sleep quality are core symptoms of sleep disorders. In addition, depressive symptoms are often reported. In the present study, we examined the possible relationships of daytime sleepiness, sleep quality and objective and subjective rated depressive symptoms in three major sleep disorders: obstructive sleep apnea (OSA; n = 25), restless legs syndrome (RLS; n = 18) and psychophysiological insomnia (n = 21), compared to healthy controls (n = 33).

Otherwise healthy subjects without a history of psychiatric disorder or psychotropic medication use were included. The Epworth Sleepiness Scale (ESS) for daytime sleepiness assessment and the Pittsburg Sleep Quality Inventory (PSQI) for subjective sleep quality were administered. Participants filled in the Beck Depression Inventory (BDI) as indicator of subjective rated depression and underwent a standard psychiatric interview; observer ratings comprised the Hamilton Depression Scale (HAMD) and the Hamilton Anxiety Scale (HAMA).

As expected daytime sleepiness was highest in OSA, whereas insomnia patients showed the highest depression and anxiety scores and the worst subjective sleep assessment. In contrast to the HAMD, the BDI was unable to differentiate among patient groups. Objective (HAMD) and subjective (BDI) rated depression correlated significantly in insomnia, RLS and healthy controls, but surprisingly not in OSA. Subjective rated depression (BDI) correlated significantly with subjective sleep quality (PSQI) in these patients. This correlation was not present in insomnia, RLS or controls. Therefore, increased BDI levels in OSA are possibly related to disturbed sleep (PSQI) rather than to depression.