Classification of sleep disorders

The classification of sleep disorders is necessary to discriminate among disorders in order to facilitate an understanding of the symptoms, etiology, pathophysiology, and treatment. The earliest sleep classification system was organized largely according to the major symptoms-insomnia, excessive sleepiness, and abnormal events that occur during sleep-because the pathophysiologic basis for many of the sleep disorders was unknown. The latest edition of the International Classification of Sleep Disorders, Second Edition (ICSD-2), published in 2005, combines a symptomatic presentation (insomnia) with one organized in part on the basis of pathophysiology (circadian rhythms) and in part on body systems (breathing disorders). This organization is necessary because of the varied nature of the sleep disorders and because the pathophysiology for many of the disorders is unknown. The ICSD-2 is not only a listing of the sleep disorders but also a text manual that lists relevant information about the diagnostic features and epidemiology to help the reader more easily differentiate among the disorders.