Clinical significance of night-to-night sleep variability in insomnia

Objectives: To evaluate the clinical relevance of night-to-night variability of sleep schedules and insomnia symptoms. Methods: The sample consisted of 455 patients (193 men, mean age = 48) seeking treatment for insomnia in a sleep medicine clinic. All participants received group cognitive behavioral therapy for insomnia (CBTI). Variability in sleep parameters was assessed using sleep diary data. Two composite scores were computed, a behavioral schedule composite score (BCS) and insomnia symptom composite score (ICS). The Insomnia Severity Index, the Beck Depression Inventory, and the Morningness-Eveningness Composite Scale were administered at baseline and post-treatment. Results: Results revealed that greater BCS scores were significantly associated with younger age, eveningness chronotype, and greater depression severity (p<0.001). Both depression severity and eveningness chronotype independently predicted variability in sleep schedules (p<0.001). Finally, CBTI resulted in reduced sleep variability for all sleep diary variables except bedtime. Post-treatment symptom reductions in depression severity were greater among those with high versus low baseline BCS scores (p<0.001). Conclusions: Results suggest that variability in sleep schedules predict reduction in insomnia and depressive severity following group CBTI. Schedule variability may be particularly important to assess and address among patients with high depression symptoms and those with the evening chronotype.