The reliability of objective total sleep time in predicting the effectiveness of cognitive-behavioral therapy for insomnia

Background: Despite insomnia diagnosis is based only on subjective sleep assessment, recent literature suggested the usefulness of objective sleep duration for the identification of two insomnia phenotypes based on objective total sleep time (oTST). In particular, insomnia with short sleep duration (SS) (oTST<6 h) seems to receive less benefit from Cognitive-Behavioral Therapy for Insomnia (CBT-I) compared to patients with normal sleep duration (NS) (oTST≥6 h). The aim of this study is to evaluate CBT-I response of patients previously divided into SS and NS and to assess the agreement between oTST measured by polysomnography (PSG) and by actigraphy in identifying the two subgroups. Methods: Fifty-three insomnia patients (50.9% females; mean age 56.53 ± 11.43) underwent a baseline PSG and an actigraphic evaluation to identify SS and NS subjects. Insomnia Severity Index (ISI) and sleep diaries data (wakefulness after sleep onset) were considered primary outcomes. All the other sleep diaries variables were used as secondary outcomes. Results: Throughout PSG we identified 22 NS (41.5%) and 31 SS (58.5%) patients, whereas actigraphic evaluation identified 38 NS (71.7%) and 15 SS (28.3%) patients. All subjects showed significant improvement after treatment, however, no effect of group membership was found to influence CBT-I response. Strikingly, actigraphy and PSG differed in identifying the two subgroups. Specifically, only 27 out 53 (51%) were consistently classified as SS [K = 0.086, 95% confidence interval: -0.132 to 0.305, p = 0.448]. Conclusions: Our results challenge the reliability and usefulness of oTST in predicting CBT-I effectiveness. Future studies might focus on night-to-night variability experienced by insomnia patients for the prediction of CBT-I outcomes.