Comparison of the effects of cognitive-behavioral therapy for insomnia between patients with primary insomnia and comorbid insomnia

Cognitive behavioral therapy for insomnia (CBT-I) is effective for not only primary insomnia (PI) but also comorbid insomnia (CI; insomnia associated with psychiatric/physical diseases or other types of sleep disorders). This study aimed to compare the outcomes of CBT-I implemented in the same manner between patients with PI and CI. In total, 41 adult patients who had completed CBT-I were enrolled in this retrospective analysis and divided into a PI group and a CI group. The authors then examined and compared the significance of changes after therapy between the two groups. The magnitude of improvement on the Japanese version of the Insomnia Severity Index (ISI-J) was analyzed as the primary endpoint. In the PI group (n = 24), both the ISI-J score and the dose of hypnotics decreased significantly following CBT-I. On the other hand, in the CI group (n = 17), only the dose of hypnotics decreased significantly; no statistically significant improvement was seen in the ISI-J score. Sleep onset latency and sleep quality rating in recorded sleep diaries were significantly correlated with improved ISI-J scores in the CI group only. CBT-I was shown to be effective for CI, but its efficacy for CI was inferior to that for PI in terms of impact on sleep and mental condition. These results suggest that in addition to the basic components of CBT-I, treatment for CI, especially when accompanied by severe insomnia symptoms, should include approaches targeting the comorbid disease.