Impact of phenotypic heterogeneity of insomnia on the patients’ response to cognitive-behavioral therapy for insomnia: Current perspectives

Insomnia is one of the most common mental disorders and the most frequent sleep disorder encountered in clinical practice, with a prevalence of about 7% in the European population. Insomnia Disorder (ID) is defined as a disturbance of sleep initiation or maintenance, followed by a feeling of non-restorative sleep and several diurnal consequences ranging from occupational and social difficulties to cognitive impairment. Cognitive-Behavioral Therapy for Insomnia (CBT-I) is considered the first-choice therapy for this disorder because its effectiveness has been proven to be greater in the long term with fewer side effects in comparison to pharmacotherapy. Although its effectiveness has been well established, it has been reported that nearly 40% of patients do not achieve remission after treatment. This finding could be the consequence of heterogeneity of ID between patients. It has been proposed that this heterogeneity might be ascribable to indices that are not related to sleep quality and quantity, such as comorbidities, life events, and personality traits. However, several works focused on the role of sleep markers, in particular objective total sleep time, for the phenotypization of ID and treatment response. The aim of this work is to summarize the available scientific literature regarding the impact of ID subtype on CBT-I response.