Circadian Phase and Phase Angle Disorders in Primary Insomnia

Objectives: We aimed to identify the prevalence of circadian phase and phase angle abnormalities in patients with insomnia. Methods: We conducted a cross-sectional, multicenter study at three sleep laboratories in the United States and Australia. Patients with insomnia and healthy control participants completed a sleep log for 7 days. Circadian phase was assessed from salivary dim light melatonin onset (DLMO) time during a 12-hour laboratory visit. Results: Seventy-nine patients meeting the Research Diagnostic Criteria for Primary, Psychophysiological, Paradoxical, and/or Idiopathic Childhood Insomnia (46 females, 35.5 +/- 12.3 years [M +/- SD]) and 21 controls (14 females, 34.4 +/- 11.8 years). As compared to controls, patients with insomnia tried to initiate sleep on average at the same clock time (24: 17 +/- 1: 17 hours vs. 24: 13 +/- 1: 30 hours, respectively; p =.84) but had a later average DLMO times (20: 56 +/- 1: 55 hours, 18: 17-01: 21 vs. 22: 02 +/- 2: 02 hours, 17: 11-04: 52, respectively; p = .04). Consequently, patients with insomnia slept at an earlier circadian phase than controls (phase angle, bedtime-DLMO 2: 13 hours (+/- 1: 43) vs. 3: 10 hours (+/- 1: 08), respectively; p = .008), of whom 10% tried to sleep at or before DLMO (compared to 0 controls), and 22% tried to sleep before or within 1 hour after DLMO (compared to 6% of controls). Conclusions: A substantial proportion (10%-22%) of patients with insomnia initiate sleep at too early a circadian phase, implicating a circadian etiology for their insomnia. Outpatient circadian phase assessments should be considered to improve differential diagnoses in insomnia and to inform the development of appropriately timed circadian-based treatments.