Many types of studies including meta-analyses have identified the effectiveness of cognitive behavioral therapy for insomnia (CBT-I) in the treatment of chronic insomnia disorder [1, 2], and the therapy is currently recommended by insomnia treatment guidelines as the first-line treatment for the disorder [3, 4]. CBT-I was originally developed for treating primary insomnia (PI), however, many studies have shown that the therapy can be deemed efficacious for treating insomnia comorbid with somatic or mental diseases (CI). Recent studies have also revealed the substantial efficacy of CBT-I not only for the severity of insomnia symptoms but also for important disease-related outcomes in chronic insomnia disorder comorbid with psychiatric diseases [5, 6]. In particular, a recent finding that response to insomnia treatment mediated eventual remission from depression suggested that focused effort to improve insomnia has the potential to enhance depression treatment outcomes [7]. However, previous studies could not clarify whether the magnitude of the improvement of insomnia symptoms with CBT-I is different between PI and CI, and whether the treatment is effective for tapering the dose of hypnotics.
The study by Iwashita and his colleagues compared the outcomes of CBT-I, which was implemented with 5 sessions including sleep hygiene education, progressive muscle relaxation, sleep scheduling (sleep restriction therapy and stimulus control therapy), and a review and summary of the sessions, between patients with PI and those with CI [8]. As a result, although a substantial tapering of hypnotics was achieved in both groups, the efficacy on insomnia symptoms of CI was inferior to that of PI. This finding impressed that CBT-I consisting of standard components without including therapeutic approaches to comorbidity is less effective for CI. In this regard, previous studies indicated that patients with insomnia comorbid with depression report more unhelpful beliefs about sleep and rumination than those who experience insomnia without comorbid depression and that such cognitive problems are linked to the development of more treatment-resistant insomnia [9, 10]. Maladaptive beliefs about sleep may also serve as barriers to engagement and adherence to some of the treatment recommendations. Thus, it would be likely that maladaptive beliefs and rumination in insomnia comorbid with depression should be addressed using cognitive therapy. Besides, standard CBT-I is not always the best choice for cases of insomnia associated with sleep apnea since they possibly show the temporal aggravation of daytime sleepiness immediately after sleep restriction therapy [11].
Considering these, modification of the content of basic components or adding approaches tailored to comorbid diseases would be necessary to improve the treatment outcome of CBT-I for CI.
Footnotes
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