Insomnia Subtypes in Clinical Population According to the Insomnia Type Questionnaire (ITQ): A Multi‐Centre Study in Spanish Sleep Clinics

TL;DR

This study identifies five insomnia subtypes in Spanish sleep clinics, showing that some subtypes are more common and have different psychological traits.

Contribution

The study validates the use of the Insomnia Type Questionnaire (ITQ) for subtyping insomnia in clinical populations.

Findings

Insomnia subtypes Type 1 and Type 3 were overrepresented in sleep clinics compared to the general population.

Type 1 insomnia patients had higher depression and anxiety scores than other subtypes.

Type 3 patients were more worried about sleep, while Type 4 had the lowest depression and anxiety scores.

Abstract

The lack of robust subtyping for insomnia disorder (ID) led to its current classification as a uniform condition. A novel approach to subtyping ID developed a new tool, the insomnia type questionnaire (ITQ). Our research aimed to assess whether the ID subtypes identified in the general population could also be found in ID patients referred to sleep clinics in a multi‐centre study throughout Spain, and to gather insights for the management of complex ID patients. The ITQ classified ID patients into the five previously described subtypes: Type 1 = 35.1%, Type 2 = 12%, Type 3 = 46.7%, Type 4 = 5.8% and Type 5 = 0.4%. Compared to the general population, there was an overrepresentation of Types 1 and 3, consistently across all participating clinical centres. The total self‐reported sleep duration was 4.7 (SD 1.2) h, with no significant differences between subtypes. Type 1 patients had significantly higher scores in the Insomnia Severity Index, Inventory of Depressive Symptomatology self‐rated and State–Trait Anxiety Inventory. Type 3 patients were more worried about their sleep. Type 4 had the lowest depression and anxiety scores. ITQ subtyping showed that ID patients attending sleep clinics had high scores in depression, specially Type 1 patients, who probably need a differentiated therapeutic approach. The over‐representation of Type 3 patients suggests that they are more worried about their sleep than the other subtypes. These findings highlight the difficulties faced by sleep clinicians to treat complex and refractory‐toto‐treatment ID patients and those with comorbid insomnia.

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