13 SLEEP DISORDERS
Harrison’s Manual of Medicine
Hypersomnias (Disorders of Excessive Daytime Sleepiness)
Disorders of Circadian Rhythmicity
Disorders of sleep are among the most common problems seen by clinicians. More than one-half of adults experience at least occasional insomnia, and 15– 20% have a chronic sleep disturbance.
Approach to the Patient
Patients may complain of: (1) difficulty in initiating and maintaining sleep (insomnia); (2) excessive daytime sleepiness, fatigue, or tiredness; (3) behavioral phenomena occurring during sleep [sleepwalking, rapid eye movement (REM) behavioral disorder, periodic leg movements of sleep, etc.]; or (4) circadian rhythm disorders associated with jet lag, shift work, and delayed sleep phase syndrome. A careful history of sleep habits and reports from the sleep partner (e.g., heavy snoring, falling asleep while driving) are a cornerstone of diagnosis. Completion of a day-by-day sleep-work-drug log for at least 2 weeks is often helpful. Work and sleep times (including daytime naps and nocturnal awakenings) as well as drug and alcohol use, including caffeine and hypnotics, should be noted each day. Objective sleep laboratory recording is necessary to evaluate sleep apnea, narcolepsy, REM behavior disorder, periodic leg movements, and other suspected disorders.
Insomnia, or the complaint of inadequate sleep, may be subdivided into difficulty falling asleep (sleep-onset insomnia), frequent or sustained awakenings (sleep-offset insomnia), or persistent sleepiness despite sleep of adequate duration (nonrestorative sleep). An insomnia complaint lasting one to several nights is termed transient insomnia and is typically due to situational stress or a change in sleep schedule or environment (e.g., jet lag). Short-term insomnia lasts from a few days up to 3 weeks; it is often associated with more protracted stress such as recovery from surgery or short-term illness. Long-term (chronic) insomnia lasts for months or years and, in contrast to short-term insomnia, requires a thorough evaluation for underlying causes. Chronic insomnia is often a waxing and waning disorder, with spontaneous or stressor-induced exacerbations.
EXTRINSIC INSOMNIA Transient situational insomnia can occur after a change in the sleeping environment (e.g., in an unfamiliar hotel or hospital bed) or before or after a significant life event or anxiety-provoking situation. Treatment is symptomatic, with intermittent use of hypnotics and resolution of the underlying stress. Inadequate sleep hygiene is characterized by a behavior pattern prior to sleep and/or a bedroom environment that is not conducive to sleep. In preference to hypnotic medications, the pt should attempt to avoid stressful activities before bed, reserve the bedroom environment for sleeping, and maintain regular rising times.
PSYCHOPHYSIOLOGIC INSOMNIA Pts with this behavioral disorder are preoccupied with a perceived inability to sleep adequately at night. Rigorous attention should be paid to sleep hygiene and correction of counterproductive, arousing behaviors before bedtime. Behavioral therapies are the treatment of choice.
DRUGS AND MEDICATIONS Caffeine is probably the most common pharmacologic cause of insomnia. Alcohol and nicotine can also interfere with sleep, despite the fact that many pts use these agents to relax and promote sleep. A number of prescribed medications, including antidepressants, sympathomimetics, and glucocorticoids, can produce insomnia. In addition, severe rebound insomnia can result from the acute withdrawal of hypnotics, especially following use of high doses of benzodiazepines with a short half-life. For this reason, hypnotic doses should be low to moderate, the total duration of hypnotic therapy should be limited to 2–3 weeks, and prolonged drug tapering is encouraged.
MOVEMENT DISORDERS Patients with restless legs syndrome complain of creeping dysesthesia deep within the calves or feet associated with an irresistible urge to move the affected limbs; symptoms are typically worse at night. Treatment is with dopaminergic drugs (L-dopa or dopamine agonists). Periodic limb movement disorder consists of stereotyped extensions of the great toe and dorsiflexion of the foot recurring every 20–40 s during non-rapid eye movement sleep. This common condition is present in 1% of the general population; treatment options include dopaminergic medications or benzodiazepines.
OTHER NEUROLOGIC DISORDERS A variety of neurologic disorders produce sleep disruption through both indirect, nonspecific mechanisms (e.g., neck or back pain) or by impairment of central neural structures involved in the generation and control of sleep itself. Common disorders to consider include dementia from any cause, epilepsy, Parkinson’s disease, and migraine.
PSYCHIATRIC DISORDERS Approximately 80% of pts with mental disorders complain of impaired sleep. The underlying diagnosis may be depression, mania, an anxiety disorder, or schizophrenia.
MEDICAL DISORDERS In asthma, daily variation in airway resistance results in marked increases in asthmatic symptoms at night, especially during sleep. Treatment of asthma with theophylline-based compounds, adrenergic agonists, or glucocorticoids can independently disrupt sleep. Inhaled glucocorticoids that do not disrupt sleep may provide a useful alternative to oral drugs. Cardiac ischemia is also associated with sleep disruption; the ischemia itself may result from increases in sympathetic tone as a result of sleep apnea. Pts may present with complaints of nightmares or vivid dreams. Paroxysmal nocturnal dyspnea can also occur from cardiac ischemia that causes pulmonary congestion exacerbated by the recumbent posture. Chronic obstructive pulmonary disease, hyperthyroidism, menopause, and gastroesophageal reflux are other causes.
Insomnia treatment is usually effective. Cognitive therapy emphasizes understanding the nature of normal sleep, the circadian rhythm, the use of light therapy, and visual imagery to block unwanted thought intrusions. Behavioral modification involves bedtime restriction, set schedules, and careful sleep environment practices. Some pts benefit from low-dose sedating tricyclics (e.g., 10 mg amitriptyline) or the judicious use of benzodiazepine or its congeners. A judicious use would be either short-term (1 week) or limited use not to exceed 3 days/week.
Hypersomnias (Disorders of Excessive Daytime Sleepiness)
Differentiation of sleepiness from subjective complaints of fatigue may be difficult. Quantification of daytime sleepiness can be performed in a sleep laboratory using a multiple sleep latency test (MSLT), the repeated daytime measurement of sleep latency under standardized conditions. Common causes are summarized in Table 13-1.
Table 13-1 Evaluation of the Patient with the Complaint of Excessive Daytime Somnolence
SLEEP APNEA SYNDROME Respiratory dysfunction during sleep is a common cause of excessive daytime sleepiness and/or disturbed nocturnal sleep, affecting an estimated 2 to 5 million individuals in the U.S. Episodes may be due to occlusion of the airway (obstructive sleep apnea), absence of respiratory effort (central sleep apnea), or a combination of these factors (mixed sleep apnea). Obstruction is exacerbated by obesity, supine posture, sedatives (especially alcohol), nasal obstruction, and hypothyroidism. Sleep apnea is particularly prevalent in overweight men and in the elderly, and is often undiagnosed. Treatment consists of correction of the above factors, positive airway pressure devices, oral appliances, and sometimes surgery.
NARCOLEPSY (Table 13-2) Narcolepsy is a disorder of excessive daytime sleepiness and intrusion of REM-related sleep phenomena into wakefulness (cataplexy, hypnagogic hallucinations, and sleep paralysis). Cataplexy, the abrupt loss of muscle tone in arms, legs, or face, is precipitated by emotional stimuli such as laughter or sadness. The excessive daytime sleepiness usually appears in adolescence, and the other phenomena, variably, later in life. The prevalence is 1 in 4000. Hypothalamic neurons containing the neuropeptide orexin (hypocretin) regulate the sleep/wake cycle and have been implicated in narcolepsy. Sleep studies confirm a pathologically short daytime sleep latency and a rapid transition to REM sleep.
Table 13-2 Prevalence of Symptoms in Narcolepsy
Somnolence is treated with stimulants such as methylphenidate (10 mg bid–20 mg qid); pemoline, dextroamphetamine, and methamphetamine are alternatives. Modafinil, a novel wake-promoting agent, was recently approved for the treatment of excessive daytime sleepiness in narcolepsy; the usual dose is 200–400 mg/d given as a single dose. Adequate nocturnal sleep time and the use of short naps are other useful measures. Cataplexy, hypnagogic hallucinations, and sleep paralysis respond to the tricyclics protriptyline (10–40 mg/d) and clomipramine (25–50 mg/d) and to the selective serotonin uptake inhibitor fluoxetine (10–20 mg/d).
Disorders of Circadian Rhythmicity
Insomnia or hypersomnia may occur in disorders of sleep timing rather than sleep generation. Such conditions may be (1) organic—due to a defect in the hypothalamic circadian pacemaker, or (2) environmental—due to a disruption of entraining stimuli (light/dark cycle). Common examples of the latter include jet-lag syndrome and shift work. Delayed sleep phase syndrome is characterized by late sleep onset and awakening with otherwise normal sleep architecture. These patients usually respond to a rescheduling regimen in which bedtimes are successively delayed by 3 h/day until the desired early bedtime is achieved (chronotherapy). Advanced sleep phase syndrome moves sleep onset to the early evening hours with early morning awakening. Bright-light phototherapy in the morning hours or melatonin therapy during the evening hours may benefit pts with these disorders as well as those with jet lag and shift-work disorders.
For a more detailed discussion, see Czeisler CA, Winkleman JW, Richardson GS: Sleep Disorders, Chap. 27, p. 155, in HPIM-15.