Sleep disorders in psychiatry.

Sleep is an active state that is critical for our physical, mental, and emotional well-being. Sleep is also important for optimal cognitive functioning, and sleep disruption results in functional impairment. Insomnia is the most common sleep disorder in psychiatry. At any given time, 50% of adults are affected with 1 or more sleep problems such as difficulty in falling or staying asleep, in staying awake, or in adhering to a consistent sleep/wake schedule. Narcolepsy affects as many individuals as does multiple sclerosis or Parkinson disease. Sleep problems are especially prevalent in schizophrenia, depression, and other mental illnesses, and every year, sleep disorders, sleep deprivation, and sleepiness add billions to the national health care bill in industrialized countries. Although psychiatrists often treat patients with insomnia secondary to depression, most patients discuss their insomnia with general care physicians, making it important to provide this group with clear guidelines for the diagnosis and management of insomnia. Once the specific medical, behavioral, or psychiatric causes of the sleep problem have been identified, appropriate treatment can be undertaken. Chronic insomnia has multiple causes arising from medical disorders, psychiatric disorders, primary sleep disorders, circadian rhythm disorders, social or therapeutic use of drugs, or maladaptive behaviors. The emerging concepts of sleep neurophysiology are consistent with the cholinergic-aminergic imbalance hypothesis of mood disorders, which proposes that depression is associated with an increased ratio of central cholinergic to aminergic neurotransmission. The characteristic sleep abnormalities of depression may reflect a relative predominance of cholinergic activity. Antidepressant medications presumably reduce rapid eye movement (REM) sleep either by their anticholinergic properties or by enhancing aminergic neurotransmission. Intense and prolonged dreams often accompany abrupt withdrawal from antidepressant drugs, a reflection of an REM rebound after drug-induced REM deprivation. The postulated link between sleep and psychiatric disorders has been reinforced by the findings of modern neurobiology.