Sleep Disorders

Background

Sleep disorders are among the most common clinical problems encountered in medicine and psychiatry. Sleep problems can be primary or result from a variety of psychiatric and medical conditions. Inadequate or nonrestorative sleep can markedly impair a patient's quality of life.^[1]
Primary sleep disorders result from an endogenous disturbance in sleep-wake generating or timing mechanisms, often complicated by behavioral conditioning. Primary sleep disorders are subdivided into parasomnias and dyssomnias. Parasomnias are unusual experiences or behaviors during sleep and include sleep terror disorder and sleepwalking (which occur during Stage 4 sleep) and nightmare disorder (which occurs during REM sleep). 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.
Assessing if a sleep disorder is primary or secondary is important. At times, assessing if anxiety and depression are causing sleep problems or if the anxiety and depression are secondary to a primary sleep problem is difficult. See Medscape's Anxiety Disorders and Depression Resource Centers.
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 are often found when people aver to experiencing 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 various physiologic, biologic, behavioral, and EEG parameters responsible for REM (ie, active) sleep and NREM (slow-wave) sleep.

Epidemiology

Frequency

United States

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% of adults 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 and accompanying danger of suicide, anxiety, excess disability, reduced quality of life, and increased use of health care resources.
• Insufficient sleep can result in industrial and motor vehicle crashes, somatic symptoms, cognitive dysfunction, depression, and decrements in daytime work performance owing to fatigue or sleepiness.
• Yaffe et al suggest that older women with sleep-disordered breathing (characterized by recurrent arousals from sleep and intermittent hypoxemia) have an increased risk of developing cognitive impairment compared with those without sleep-disordered breathing.^[2]

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).
• People who are elderly 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.
• People who are elderly may have widespread or multisite pain that is associated with sleep difficulty, according to the Maintenance of Balance, Independent Living, Intellect, and Zest in the Elderly study (MOBILIZE) study.^[3]