sleep disorders I

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Sleep disorders are among the most common clinical problems encountered in medicine, including in psychiatry. The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) divides all sleep disorders into 3 general groups: primary, secondary to a mental disorder, and others, namely those related to a general medical condition or substance abuse.

Primary sleep disorders are presumed to result from an endogenous disturbance in sleep-wake generating or timing mechanisms, often complicated by behavioral conditioning. These disorders are further subdivided into parasomnias and dyssomnias. Parasomnias are characterized by abnormal behavioral or physiological events in association with sleep, sleep stages, or sleep-wake transitions, rather than increased or decreased sleep. Parasomnias include nightmare disorder, sleep terror disorder, and sleepwalking disorder. Dyssomnias are characterized by abnormalities in the amount, quality, or timing of sleep. These include primary insomnia and hypersomnia, narcolepsy, breathing-related sleep disorder (ie, sleep apnea), and circadian rhythm sleep disorder. This article focuses primarily on insomnia, rather than the numerous other sleep disorders.

Primary insomnia is the general term for difficulty in initiating or maintaining sleep. Because sleep requirements vary from individual to individual, insomnia is considered clinically significant when a patient perceives the loss of sleep as a problem. Insomnia may be characterized further as acute (transient) or chronic.

Pathophysiology:

Rapid eye movement and nonrapid eye movement

Sleep is divided into 2 categories, rapid eye movement (REM) and nonrapid eye movement (NREM). Each of these sleep states is associated with distinct central nervous system activity.

NREM sleep is further divided into 4 progressive categories, termed stages 1-4 sleep. The arousal threshold rises with each stage of sleep, with stage 4 (delta) being the sleep state from which a person is least able to be aroused, characterized by high-amplitude slow waves.

REM sleep is characterized by muscle atonia, episodic REMs, and low-amplitude fast waves on electroencephalogram (EEG) readings. Dreaming occurs mainly during REM sleep.

Disturbances in the pattern and periodicity of REM and NREM sleep often are found when people complain of sleep disorders.

Sleep-wake cycles

Sleep-wake cycles are governed by a complex group of biological processes that serve as internal clocks.

The suprachiasmatic nucleus, located in the hypothalamus, is thought to be the body's anatomic timekeeper, responsible for the release of melatonin on a 25-hour cycle.

The pineal gland secretes less melatonin when exposed to bright light; therefore, the level of this chemical is lowest during the daytime hours of wakefulness.

Multiple neurotransmitters are thought to play a role in sleep. These include serotonin from the dorsal raphe nucleus, norepinephrine contained in neurons with cell bodies in the locus ceruleus, and acetylcholine from the pontine reticular formation. Dopamine, on the other hand, is associated with wakefulness.

Abnormalities in the delicate balance of all of these chemical messenger systems may disrupt a variety of physiologic, biologic, behavioral, and EEG parameters responsible for REM (ie, active) sleep and NREM (slow-wave) sleep.

Frequency:

In the US: Approximately one third of all Americans have sleep disorders at some point in their lives. Approximately 20-40% of adults report difficulty sleeping at some point each year. Approximately 17% consider the problem to be serious. Sleep disorders are a common reason for patient visits throughout medicine. Approximately one third of adults have insufficient sleep syndrome. Twenty percent of adults report chronic insomnia.
Mortality/Morbidity:

Chronic insomnia is associated with an increased risk of depression, anxiety, excess disability, reduced quality of life, and increased use of health care resources.
Insufficient sleep can result in industrial and motor vehicle accidents, somatic complaints, cognitive dysfunction, depression, and decrements in daytime work performance owing to fatigue or sleepiness.
Sex:

Primary insomnia is more common in women, with a female-to-male ratio of 3:2. Hormonal variations during the menstrual cycle or during menopause may cause disruptions in sleep.
Obstructive sleep apnea is more common in men (4%) than in women (2.5%).
Age:

Increasing age predisposes to sleep disorders (5% in persons aged 30-50 y and 30% in those aged 50 y or older).
Elderly people experience a decrease in total sleep time, with more frequent awakenings during the night.
People who are elderly have a higher incidence of general medical conditions and are more likely to be taking medications that cause sleep disruption.

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