Insomnia is defined as difficulty with the initiation, maintenance, duration, or quality of sleep that results in the impairment of daytime functioning, despite adequate opportunity and circumstances for sleep.1,2 (Difficulty with sleep maintenance implies waking after sleep has been initiated but before a desired wake time.) Most research studies adopt an arbitrary definition of a delay of more than 30 minutes in sleep onset or a sleep efficiency (the ratio of time asleep to time in bed) of less than 85 percent.1 However, in clinical practice, a patient's subjective judgment of sleep quality and quantity is a more important factor. Transient insomnia lasts less than one week, and short-term insomnia one to four weeks.
Chronic insomnia — insomnia lasting more than one month3 — has a prevalence of 10 to 15 percent2,4 and occurs more frequently in women, older adults, and patients with chronic medical and psychiatric disorders.1 It may follow episodes of acute insomnia in patients who are predisposed to having the condition and may be perpetuated by behavioral and cognitive factors, such as worrying in bed and holding unreasonable expectations of sleep duration.5 Consequences include fatigue, mood disturbances, problems with interpersonal relationships, occupational difficulties, and a reduced quality of life.
Taking a careful history from the patient and a bed partner, if present, usually allows accurate categorization of the causes of insomnia. Asking the patient to keep a diary documenting times of sleep for one to four weeks may be helpful. Polysomnography is rarely needed unless there is a strong suspicion of sleep-disordered breathing or periodic limb movement disorder or unless insomnia fails to respond to treatment.6