Abstract 18 Poster Session III, Monday, 5/3 (poster 257)

Background: Delayed sleep phase syndrome (DSPS) is an increasingly recognised sleep disorder associated with suboptimal performance at school or work. International Classification of Sleep Disorders (ICSD) criteria for diagnosis are a) an inability to fall asleep or spontaneously awaken at desired clock times, b) a phase delay of the major sleep episode, c) symptoms present for at least 1 month, d) normal sleep when strict schedules are not necessary (e.g., vacation), and e) illustration of sleep delay with a two-week sleep log. Potential pharmacologic treatments include melatonin analogues. Published estimates of its prevalence range from 0.17% in a sample of adults to 7.3% in a sample of students. A large school-based survey was undertaken to address uncertainty in prevalence of DSPS due to variability in sampling, study design and case definition in previous studies. The study is unique in that there was clinical verification of diagnosis in participants with possible DSPS.

Methods: Students attending grades 7 through 12 in Halifax Nova Scotia schools, serving a mixed urban-rural municipality (pop. 330,000), were selected using stratified single-stage proportional allocation cluster sampling. Subjects filled out a modified School Sleep Habits Survey (©Mary Carskadon 1994, Bradley Hospital/Brown University Sleep Research Laboratory, Rhode Island) and the Beck Depression Inventory. Students who met one or more criteria for DSPS on survey responses were asked to complete a three-week sleep diary and to meet with a psychiatrist to establish a diagnosis of DSPS, Motivated Sleep Phase Delay (MSPD), initial insomnia or other disorder. Univariate analyses were adjusted for survey design using Stata Statistical Software.

Results: 1743 students took part in the survey (46% male, 54% female) of whom 1712 had evaluable data. Participants ranged in age from 12-13 (25%), 14-15 (36%), 16-17 (26%) to 18-20 (13%) with a mean age of 15. 17% reported delayed sleep onset (≥60 minutes to fall asleep on school days). 64 students with possible DSPS were invited up to 3 times for psychiatric interviews and 25 complied. Interview confirmed that 9 of 25 participants met 4 of 5 ICSD criteria for a prevalence of 0.53% (95% CI: 0.24 - 1.0%). 5 of the 9 participants did not return their sleep logs, which is required for evaluation of the fifth ICSD criterion. Assuming the same proportion of cases in those who refused interview, an upper limit of DSPS prevalence would be 1.3%. 5 interviewed subjects who did not have DSPS had MSPD, 10 had initial insomnia and one had no sleep disorder.

Discussion: Although single components of DSPS such as delayed sleep onset are common in adolescents, DSPS meeting ICSD criteria is less common than documented in previous studies, which have relied on participant self-report without clinical verification. Which portions of the population would benefit from environmental or pharmacological interventions remains to be studied.

Funded by Servier Canada