International Classification of Sleep Disorders: A brief account of its history and of its importance for clinical practice

The International Classification of Sleep Disorders (ICSD) is an essential tool for understanding, diagnosing, and treating sleep disorders. This classification was first published in 1990 as an updated version of the consensus-based classification of sleep disorders developed in 1979. Subsequently, in 2005, following a revision made in 1997, a second edition (ICSD-2) was published, which updated and expanded the classification by introducing new categories and subcategories and updating the terminology to reflect advances in sleep research during that period. In contrast to the revised ICSD-1, which utilized a three-axis classification system (diagnosis of the disorder, procedures to detect the disorder, and medical and psychiatric conditions associated with the disorder), the ICSD-2 classification system was based only on one axis, namely the diagnosis of disorder, and focused more on the disorders themselves to provide comprehensive information on each one of them to facilitate their proper identification and treatment. Given the significant progress made in the diagnosis and treatment of these disorders over the past 20 years, a third edition and a revised version were published in 2014 and 2023, respectively, to include new disorders, new knowledge on existing disorders, and new terminology. The objective of this article is to briefly describe the main contributions of the ICSD to the understanding, diagnosis, and treatment of sleep disorders, with an emphasis on the ICSD-3-TR. It also aims to explore both the evolution of the ICSD and the importance of its use in clinical practice.