Phase-angle differences between dim-light melatonin onset and sleep onset in patients diagnosed with delayed sleep phase syndrome

Background: In current literature, the majority of the population shows a dim-light melatonin onset (DLMO) around 10pm and a phase angle difference to sleep onset of approximately 2h . But until now no study has investigated the phase angle difference between these values for extreme evening types, namely patients diagnosed with delayed sleep phase syndrome (DSPS) . Therefore, we collected DLMO as well as sleep diaries of those patients .Methods: We compared 79 patients diagnosed with DSPS at a Sleep Medicine Centre and 9 controls . The mean age was 38 .4 (SD=14 .8); 46 .6% were female . We collected saliva, melatonin and sleep diaries from all participants . The patient group was split into three subgroups according to their DLMO; G1: late bedtime, DLMO before midnight (n=17); G2: late bedtime, DLMO between 0am and 2am (N=26); G3; ultra late bedtime, DLMO after 2am (n=36) . ANOVA (w/ Bonferroni correction) was used for statistical analysis .Results: Controls mean DLMO was 10:21pm, the patients subgroups DLMO was 10:49pm (G1); 0:48am (G2) and 3:25am (G3); the groups differed significantly from each other (except G1 and controls) . The reported sleep onset was 23:59pm in controls, 03:36am (G1); 02:20am (G2) and 03:34am (G3) . The groups were all different between them with the exception of G1 and G3 . The phase angle differences were 1:41h (controls), 4:46h (G1); 1:33h (G2) and 00:08h (G3) . Phase angle differences differed significantly between groups, with the exception of G2 and controls . There were no significant group differences for age .Conclusions: G1 showed late sleeping schedules but showed a DLMO close to the controls . We therefore considered them a “behavioural evening group” . G3 showed the latest DLMO and the least phase angle difference, therefore called “sleep phase delay” . The phase angle difference was only similar between G2 and the healthy group . For the extreme sleep onset groups (G1, G3), there were statistically significant differences in DLMO and sleep onset phase angle . This study enhances the importance of DLMO measurement for therapeutically intervention, suggesting the sleep diary as a poor indicator of circadian phase in DSPD patients . Furthermore, melatonin DLMO does not explain all late bedtimes . Diagnosis should be complemented by objective sleep onset measures, such as actimetry or polysomnography.