Nonrestorative sleep as a distinct component of insomnia

Abstract

Study objectives: Explore characteristics of nonrestorative sleep (NRS) in prospectively defined subgroups of individuals with NRS symptoms, investigate whether NRS can occur independently of difficulties initiating and maintaining sleep (DIS/DMS), and determine its effect on waking function.

Design: Cross-sectional and longitudinal population-based study comparing patterns of daytime symptoms, and their persistence, in cohorts of subjects with NRS symptoms grouped according to presence or absence of DIS and DMS.

Setting: 28 sleep centers in the US.

Participants: Subjects reporting awakening unrestored or unrefreshed at least 3 times weekly over the previous 3 months were classified, based on self-reported sleep problems, to DIS (n = 138), DMS (n = 44), DIS+DMS (n = 125), and NRS-only (no DIS or DMS; n = 192) cohorts. Eighty healthy volunteers formed a control group.

Interventions: None.

Measurements and results: Polysomnography confirmed DIS and/or DMS in 56/138 (41%), 18/44 (41%), and 37/125 (30%) subjects in DIS, DMS, and DIS+DMS cohorts, respectively; and absence of DIS or DMS in 115/192 (60%) NRS-only subjects and 52/80 (65%) healthy volunteers. Multiple subject-reported endpoints including the Endicott Work Productivity Scale, Pittsburgh Insomnia Rating Scale, Restorative Sleep Questionnaire, and SF-36, showed that NRS-only subjects had significantly impaired daytime function relative to healthy volunteers, comparable to impairment affecting subjects with DIS and/or DMS. Symptoms persisted over 3 months.

Conclusions: This study confirms that NRS can occur independently of other components of insomnia. Daytime symptoms were as severe in individuals with NRS-only as those whose NRS symptoms were combined with DIS or DMS.

Figure 1

Mean (SD) Endicot Work Productivity Scale (EWPS) scores in NRS cohorts, with and without DIS/DMS, and healthy volunteers. DIS, difficulty initiating sleep; DMS, difficulty maintaining sleep; NRS, nonrestorative sleep; SD, standard deviation

Figure 2

Restorative sleep and daytime consequences in subjects with NRS symptoms, with and without DIS/DMS, and healthy volunteers, mean (SD) scores on the Restorative Sleep Questionnaire (RSQ)-Weekly (A), RSQ-Daily (B), and Daytime Consequences of Sleep Questionnaire (DCSQ) (C) DIS, difficulty initiating sleep; DMS, difficulty maintaining sleep; NRS, nonrestorative sleep; SD, standard deviation

Figure 3

Clinician-rated symptom severity for subjects with DIS, DMS, DIS+DMS, and NRS-only, and healthy volunteers, mean (SD) Clinical Global Impression of Severity (CGIS) scores. DIS, difficulty initiating sleep; DMS, difficulty maintaining sleep; NRS, nonrestorative sleep; SD, standard deviation

Figure 4

Polysomnography-measured sleep parameters in DIS, DMS, DIS+DMS, NRS-only, and healthy volunteer cohorts, latency to persistent sleep (LPS) (A) and wake after sleep onset (WASO) (B) DIS, difficulty initiating sleep; DMS, difficulty maintaining sleep; NRS, nonrestorative sleep

Figure 5

Time spent in stage 3/4 sleep (A) or REM sleep (B) over the 8-hour polysomnography period (mean for each hour on Days 9/10). PSG, polysomnography