Introduction The International Classification of Sleep Disorders (ICSD-2)  classification lists 85 sleep disorders in eight major categories, each presented in detail with a descriptive diagnostic text that includes specific diagnostic criteria: (1) the insomnias; (2) the sleep-related breathing disorders; (3) the hypersomnias not due to a breathing disorder; (4) the circadian rhythm sleep disorders; (5) the parasomnias; (6) the sleep-related movement disorders; (7) other sleep disorders; and (8) isolated symptoms, apparently normal variants and unresolved issues. The ICSD-2 also includes in its appendices: Sleep disorders that are associated with conditions classifiable elsewhere (Appendix A); as well as Other psychiatric and behavioral disorders frequently encountered in the differential diagnosis of sleep disorders (Appendix B) (seeTable 13.1). Insomnias The insomnias are defined by the symptom of difficulty with sleep initiation and/or maintenance, and final awakenings that occur earlier than the desired wake-up time. There can also be a complaint of non-restorative sleep or poor sleep quality. Such symptoms occur despite adequate time and opportunity for sleep and result in some form of daytime impairment. The insomnias can be either primary or secondary. Secondary forms of insomnia can occur when insomnia is a symptom of a medical or psychiatric illness, other sleep disorders, or substance abuse. Primary sleep disorders are those that can have both intrinsic and extrinsic factors involved in their etiology but are not regarded as having causes secondary to those disorders that can result in (secondary) insomnia. Although not specifically discussed in the ICSD-2, the term comorbid insomnia is now championed by many sleep experts as the more appropriate term to describe many secondary insomnias.
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