Medical School · Year 3 · Neurology · includes a quiz and discussion video

Seminar 13: Sleep Disorders in Neurology

Neurology Clerkship

Learning Objectives

By the end of this seminar, students will be able to:

1. Describe normal sleep architecture and physiology
2. Evaluate patients with excessive daytime sleepiness
3. Diagnose and manage common sleep disorders
4. Recognize narcolepsy and its clinical features
5. Identify parasomnias and REM sleep behavior disorder
6. Apply sleep testing modalities appropriately

Seminar Outline

Section 1: Sleep Physiology

Normal sleep is organized into distinct stages that cycle throughout the night, each characterized by unique electroencephalographic patterns and physiological features. Stage N1 represents light sleep, during which theta waves predominate on the EEG and the individual can be easily aroused by external stimuli. Stage N2 is defined by the presence of sleep spindles and K-complexes and constitutes the largest proportion of total sleep time, accounting for approximately 45 to 55 percent of the night. Stage N3, also known as slow-wave sleep, is characterized by high-amplitude delta waves and serves a restorative function essential for physical recovery and immune function. REM sleep is distinguished by rapid eye movements, vivid dreaming, and generalized skeletal muscle atonia that prevents the physical enactment of dream content.

Sleep architecture follows a predictable pattern organized into approximately 90-minute cycles, with four to six complete cycles occurring during a typical night. The distribution of sleep stages across the night is not uniform; slow-wave sleep predominates during the early portion of the night, reflecting the brain's prioritization of deep restorative sleep when homeostatic sleep pressure is highest, while REM sleep becomes increasingly prominent during the later cycles toward morning. REM sleep constitutes approximately 20 to 25 percent of total sleep time in healthy adults, and this proportion is clinically relevant because several sleep disorders, including narcolepsy and REM sleep behavior disorder, involve pathological alterations in the timing, amount, or characteristics of REM sleep.

The circadian rhythm system governs the approximately 24-hour oscillation in sleep-wake propensity and is controlled by the suprachiasmatic nucleus, the master biological clock located in the hypothalamus. Melatonin, produced by the pineal gland during darkness, serves as a hormonal signal that promotes sleep onset and reinforces the circadian night. Light exposure is the most powerful environmental cue, or zeitgeber, that entrains the circadian rhythm to the external light-dark cycle, and this principle underlies the therapeutic use of bright light therapy for circadian rhythm disorders. Core body temperature follows a circadian pattern as well, dropping during the biological night to facilitate sleep onset and maintenance.

Sleep is regulated by two fundamental processes that interact to determine the timing and intensity of sleep. The homeostatic process reflects the accumulation of sleep pressure during wakefulness, such that the longer an individual remains awake, the stronger the drive to sleep becomes. The circadian process provides a rhythmic modulation of alertness that operates independently of prior sleep or wakefulness, promoting wakefulness during the biological day and facilitating sleep during the biological night. At the neurochemical level, adenosine accumulates in the brain during sustained wakefulness and promotes sleep by inhibiting wake-promoting neurons, which explains why caffeine, an adenosine receptor antagonist, promotes alertness. The orexin system, also known as the hypocretin system, plays a critical role in stabilizing wakefulness by activating arousal centers throughout the brain, and the selective loss of orexin-producing neurons in the lateral hypothalamus is the pathological basis of narcolepsy type 1.

<image>Sleep physiology: stages, architecture, circadian rhythm, regulation</image>

Section 2: Approach to Sleep Disorders

A thorough sleep history is the cornerstone of evaluating any patient with a suspected sleep disorder and should systematically address several key elements. The clinician should first establish the patient's habitual sleep schedule, including typical bedtime, wake time, and the frequency and duration of daytime naps. Sleep quality is assessed by asking about difficulty initiating sleep, difficulty maintaining sleep with frequent nighttime awakenings, and early morning awakening with inability to return to sleep. Daytime symptoms including excessive sleepiness, fatigue, and impaired concentration should be carefully characterized, as they provide important clues to the underlying diagnosis and its functional impact. The bed partner's observations are invaluable and should specifically address the presence of snoring, witnessed apneic episodes, and abnormal movements during sleep. Finally, sleep hygiene practices including caffeine consumption, alcohol use, and evening screen time exposure should be reviewed, as these modifiable factors frequently contribute to or exacerbate sleep complaints.

Several validated tools assist in the objective assessment of sleepiness and screening for specific sleep disorders. The Epworth Sleepiness Scale is an eight-item self-report questionnaire that asks patients to rate their likelihood of dozing in various everyday situations, with a score greater than 10 indicating abnormal daytime sleepiness warranting further evaluation. The STOP-BANG questionnaire is a widely used screening tool specifically designed to identify patients at risk for obstructive sleep apnea based on symptoms, body habitus, and demographic features. A two-week sleep diary provides a detailed prospective record of sleep-wake patterns, bedtimes, wake times, and perceived sleep quality that is particularly useful in diagnosing insomnia and circadian rhythm disorders. Actigraphy, which employs a wrist-worn activity monitor to record movement patterns over days to weeks, provides an objective estimate of sleep-wake patterns in the patient's natural environment and is especially useful for evaluating circadian rhythm disorders and monitoring treatment response.

Sleep disorders are classified into six major categories according to the International Classification of Sleep Disorders. Insomnia disorders, exemplified by chronic insomnia disorder, involve difficulty initiating or maintaining sleep despite adequate opportunity. Sleep-related breathing disorders include obstructive sleep apnea and central sleep apnea. Central disorders of hypersomnolence encompass conditions characterized by excessive daytime sleepiness not attributable to other sleep disorders, with narcolepsy and idiopathic hypersomnia being the principal diagnoses. Circadian rhythm sleep-wake disorders result from misalignment between the internal circadian clock and the desired or required sleep-wake schedule, and include delayed sleep phase disorder and shift work disorder. Parasomnias are undesirable events or experiences that occur during sleep, such as sleepwalking and REM sleep behavior disorder. Sleep-related movement disorders include restless legs syndrome and periodic limb movement disorder.

Diagnostic testing in sleep medicine is guided by the clinical presentation and the specific disorder suspected. Polysomnography, the comprehensive overnight laboratory-based sleep study, is the gold standard diagnostic tool and is indicated for the evaluation of obstructive sleep apnea, parasomnias, and narcolepsy, recording multiple physiological parameters including EEG, electromyography, electrooculography, airflow, respiratory effort, and oxygen saturation. Home sleep apnea testing offers a more convenient and cost-effective alternative for diagnosing uncomplicated obstructive sleep apnea in patients without significant comorbidities. The multiple sleep latency test is the standard diagnostic tool for narcolepsy and measures how quickly a patient falls asleep and whether REM sleep occurs during five scheduled daytime nap opportunities. The maintenance of wakefulness test assesses the ability to remain awake in a quiet, soporific setting and is used to evaluate the adequacy of treatment response in patients with disorders of excessive sleepiness, particularly when safety concerns such as driving or operating machinery are relevant.

<image>Sleep disorders: history, assessment, categories, testing</image>

Section 3: Obstructive Sleep Apnea

Obstructive sleep apnea is a highly prevalent condition affecting approximately 2 to 4 percent of the general population, though it remains significantly underdiagnosed. The major risk factors include obesity, which is the strongest modifiable risk factor due to fatty tissue deposition around the upper airway, male sex, advancing age, and craniofacial abnormalities that predispose to airway narrowing. The clinical significance of obstructive sleep apnea extends well beyond its effects on sleep quality, as it is independently associated with significant cardiovascular morbidity including hypertension, type 2 diabetes mellitus, stroke, and atrial fibrillation, making its diagnosis and treatment essential for both neurological and general medical reasons.

The clinical presentation of obstructive sleep apnea involves a constellation of nocturnal and daytime symptoms that reflect the repeated episodes of upper airway obstruction during sleep. Loud, disruptive snoring is the most commonly reported symptom and is typically noted by the bed partner rather than the patient. Witnessed apneas, in which the bed partner observes the patient stop breathing for several seconds followed by a gasping or choking resumption of respiration, are highly suggestive of the diagnosis. Daytime sleepiness results from the sleep fragmentation caused by repeated arousals and is characteristically described as unrefreshing sleep despite apparently adequate sleep duration. Morning headache, attributed to nocturnal hypercapnia, is a frequently reported symptom. Nocturia, resulting from atrial natriuretic peptide release triggered by the hemodynamic effects of obstructive events, leads to multiple nighttime awakenings to urinate. Cognitive symptoms including impaired memory and difficulty with concentration are common and may be the presenting complaint.

The diagnosis of obstructive sleep apnea is established through polysomnography or home sleep apnea testing, which quantify the frequency and severity of respiratory events during sleep. The Apnea-Hypopnea Index, or AHI, is the primary metric used to define the presence and severity of the disorder and represents the average number of apneas and hypopneas per hour of sleep. Mild obstructive sleep apnea is defined by an AHI of 5 to 15 events per hour, moderate by an AHI of 15 to 30, and severe by an AHI greater than 30, with the severity classification guiding treatment decisions and prognostic counseling.

Treatment of obstructive sleep apnea is multimodal and is tailored to the severity of disease and individual patient factors. Continuous positive airway pressure, or CPAP, is the first-line treatment for moderate to severe obstructive sleep apnea and works by pneumatically splinting the upper airway open during sleep. Weight loss is recommended for all overweight patients and can substantially reduce AHI, with some patients achieving complete resolution of the disorder. Positional therapy, which involves techniques to avoid sleeping in the supine position, is effective for the subset of patients whose obstructive events occur predominantly or exclusively in the supine position. Oral appliances, which advance the mandible forward to enlarge the retrolingual airway space, are an alternative for patients with mild to moderate disease or those who cannot tolerate CPAP. Surgical options, including uvulopalatopharyngoplasty, are considered for select patients who have failed or cannot use other treatments. Hypoglossal nerve stimulation is a newer therapeutic option for patients who have failed CPAP therapy, using an implanted device to stimulate the hypoglossal nerve and activate the genioglossus muscle to maintain airway patency during sleep.

<image>Obstructive sleep apnea: risk factors, features, diagnosis, treatment</image>

Section 4: Central Sleep Apnea

Central sleep apnea comprises a group of disorders in which apneic events occur due to transient cessation of respiratory drive from the brainstem rather than physical obstruction of the upper airway. Primary or idiopathic central sleep apnea occurs without an identifiable underlying cause. Cheyne-Stokes respiration is the most clinically important form of central sleep apnea and is characterized by a cyclic crescendo-decrescendo pattern of breathing that waxes and wanes in tidal volume, occurring most commonly in patients with heart failure. High-altitude central sleep apnea results from the hyperventilatory response to hypoxia that drives the partial pressure of carbon dioxide below the apneic threshold. Opioid-induced central sleep apnea occurs through direct depression of brainstem respiratory centers by narcotic medications. Treatment-emergent central sleep apnea is a distinct entity in which central apneic events develop or persist after the institution of CPAP therapy for obstructive sleep apnea.

The pathophysiology of central sleep apnea centers on instability in the ventilatory control system rather than mechanical airway compromise. The fundamental mechanism involves reduced respiratory drive from brainstem respiratory centers, which may result from intrinsic brainstem dysfunction, circulatory delay in heart failure, or suppression by medications. The concept of loop gain describes the sensitivity of the ventilatory feedback system, with high loop gain indicating an exaggerated ventilatory response to small perturbations in carbon dioxide levels that leads to overshoot and undershoot of ventilation, producing the characteristic oscillatory breathing pattern. The apneic threshold for carbon dioxide is the level below which respiratory drive ceases, and in patients with elevated loop gain, even small reductions in carbon dioxide during a hyperpneic phase can drive the level below this threshold and trigger a central apneic event.

The diagnosis of central sleep apnea requires polysomnography, which demonstrates apneas occurring in the absence of respiratory effort, distinguishing these events from the obstructive variety in which respiratory effort persists against a closed airway. The pattern of respiratory events may be cyclic, as in the crescendo-decrescendo pattern of Cheyne-Stokes respiration, or more irregular depending on the underlying etiology. The critical distinction from obstructive sleep apnea is the absence of chest and abdominal wall movement during apneic events, indicating that the cessation of breathing is driven by a central pause in respiratory neural output rather than by upper airway obstruction.

Treatment of central sleep apnea begins with identification and management of the underlying cause, as many forms are secondary to treatable conditions. Optimization of heart failure therapy, including the use of guideline-directed medical therapy with diuretics, ACE inhibitors, and beta-blockers, can substantially reduce or eliminate Cheyne-Stokes respiration. Discontinuation or dose reduction of opioid medications should be pursued when clinically feasible for opioid-induced central sleep apnea. CPAP may benefit some patients with central sleep apnea by stabilizing the upper airway and increasing functional residual capacity. Adaptive servo-ventilation is a sophisticated positive airway pressure modality that dynamically adjusts pressure support breath-by-breath to counteract the ventilatory instability, though it is critically contraindicated in patients with heart failure with reduced ejection fraction due to evidence of increased mortality in this population. Supplemental oxygen can be beneficial in high-altitude and some other forms of central sleep apnea. Phrenic nerve stimulation, in which an implanted device stimulates the phrenic nerve to drive diaphragmatic contraction, is an emerging therapy under investigation for central sleep apnea.

<image>Central sleep apnea: types, pathophysiology, diagnosis, treatment</image>

Section 5: Narcolepsy

Narcolepsy is classified into two distinct types based on the presence or absence of cataplexy and cerebrospinal fluid orexin levels. Narcolepsy type 1, formerly known as narcolepsy with cataplexy, is characterized by the presence of cataplexy and is associated with markedly low cerebrospinal fluid orexin levels, reflecting the selective autoimmune destruction of orexin-producing neurons in the lateral hypothalamus. Narcolepsy type 2, formerly narcolepsy without cataplexy, presents with excessive daytime sleepiness and other narcolepsy features but lacks cataplexy, and cerebrospinal fluid orexin levels are typically normal, suggesting a different or partial pathological mechanism.

The clinical presentation of narcolepsy is classically described as a pentad of five cardinal symptoms, though not all patients manifest the complete syndrome. Excessive daytime sleepiness is the universal and usually most debilitating symptom, characterized by irresistible sleep attacks that may occur at inappropriate times despite apparently adequate nocturnal sleep. Cataplexy, which is pathognomonic for narcolepsy type 1, consists of sudden episodes of muscle weakness triggered by strong emotions. Hypnagogic hallucinations are vivid, often frightening, dream-like perceptual experiences that occur at the transition from wakefulness to sleep onset and reflect the intrusion of REM sleep phenomena into waking consciousness. Sleep paralysis is the temporary inability to move or speak during the transition between sleep and wakefulness, typically lasting seconds to minutes and often accompanied by a sensation of impending suffocation. Disrupted nocturnal sleep, characterized by fragmented sleep with frequent awakenings throughout the night, is a common but often underappreciated feature that paradoxically coexists with the irresistible daytime sleepiness.

Cataplexy deserves particular attention because of its diagnostic specificity and its clinical distinctiveness. Episodes are characteristically triggered by strong positive emotions such as laughter, surprise, or excitement, distinguishing them from syncope and seizures, which have different provocative circumstances. The duration of cataplectic attacks ranges from seconds to minutes, during which consciousness is fully preserved, allowing the patient to recall the entire event. The spectrum of cataplexy ranges from subtle presentations such as jaw dropping, head nodding, or knee buckling to complete postural collapse with generalized loss of muscle tone. Cataplexy is pathognomonic for narcolepsy type 1 and, when present in a patient with excessive daytime sleepiness, is virtually diagnostic of the disorder.

The diagnosis of narcolepsy is established through a combination of clinical features and objective sleep testing. The standard diagnostic protocol involves overnight polysomnography followed the next day by the multiple sleep latency test, which consists of five scheduled nap opportunities at two-hour intervals; a mean sleep latency of less than 8 minutes combined with the presence of two or more sleep-onset REM periods, known as SOREMPs, supports the diagnosis of narcolepsy. The presence of SOREMPs reflects the pathological intrusion of REM sleep at inappropriate times, which is the fundamental neurophysiological abnormality in narcolepsy. Measurement of cerebrospinal fluid orexin levels provides a definitive biomarker for narcolepsy type 1, with levels below 110 picograms per milliliter being diagnostic. The HLA allele DQB1*06:02 is present in the vast majority of patients with narcolepsy type 1 and is strongly associated with the disorder, though it is present in approximately 25 percent of the general population and therefore lacks specificity as a standalone diagnostic test.

<image>Narcolepsy: types, clinical features, cataplexy, diagnosis</image>

Section 6: Narcolepsy Treatment

The pharmacological treatment of excessive daytime sleepiness in narcolepsy aims to promote wakefulness and minimize the impact of irresistible sleep attacks on daily functioning. Modafinil is the established first-line medication for narcolepsy-related sleepiness, administered at doses of 100 to 200 milligrams daily, and is favored for its relatively favorable side effect profile compared with traditional stimulants. Armodafinil, the R-enantiomer of modafinil, has a longer half-life and may provide more sustained wakefulness throughout the day. Amphetamines serve as second-line agents and are more potent wake-promoting drugs but carry a greater burden of cardiovascular and psychiatric side effects, as well as higher abuse potential. Methylphenidate is another traditional stimulant alternative used when first-line agents are insufficient. Solriamfetol is a newer agent that acts as a dopamine and norepinephrine reuptake inhibitor and has demonstrated efficacy for excessive daytime sleepiness in narcolepsy. Pitolisant, a histamine H3 receptor antagonist and inverse agonist, represents a novel mechanism of action that promotes wakefulness by increasing histamine release in the brain.

The treatment of cataplexy requires medications that suppress REM sleep or otherwise modulate the neural circuits responsible for cataplectic attacks. Sodium oxybate is the first-line treatment for cataplexy and has the unique advantage of simultaneously treating excessive daytime sleepiness and consolidating nocturnal sleep. Serotonin-norepinephrine reuptake inhibitors, particularly venlafaxine, are effective anticataplectic agents and are commonly used due to their favorable tolerability profile. Tricyclic antidepressants, particularly clomipramine, have potent anticataplectic effects mediated through their strong norepinephrine reuptake inhibition and REM-suppressing properties, though their anticholinergic side effects limit their tolerability. Selective serotonin reuptake inhibitors can reduce cataplexy but are generally considered less effective than the other anticataplectic agents.

Sodium oxybate occupies a central role in narcolepsy management due to its broad efficacy across multiple symptom domains. Its mechanism of action involves agonism at GABA-B receptors, which consolidates sleep architecture and reduces the dissociation between sleep and wake states that characterizes narcolepsy. The dosing regimen is unique among sleep medications, requiring two doses nightly: the first taken at bedtime and the second taken 2.5 to 4 hours later, reflecting its short duration of action. Sodium oxybate effectively reduces cataplexy frequency, improves excessive daytime sleepiness, and consolidates the disrupted nocturnal sleep that is characteristic of narcolepsy. Important safety considerations include the risk of respiratory depression, particularly when combined with other central nervous system depressants, and its abuse potential, which has led to its classification as a Schedule III controlled substance with a mandatory risk evaluation and mitigation strategy program.

Lifestyle modifications are an important adjunct to pharmacological therapy and should be incorporated into every narcolepsy management plan. Scheduled short naps of 15 to 20 minutes, strategically timed during the day, are remarkably refreshing for narcolepsy patients and can significantly improve alertness during the intervening periods of wakefulness. Consistent sleep hygiene practices, including maintaining a regular sleep-wake schedule seven days a week, help stabilize the fragmented sleep-wake patterns that characterize the disorder. Safety counseling is critical and should address the risks associated with driving and operating heavy machinery, as sudden sleep attacks can have catastrophic consequences; patients should be informed of legal requirements regarding driving restrictions and should be counseled to avoid driving when excessively sleepy. Patient education about the chronic nature of the disorder and referral to support groups can help patients cope with the psychological and social impact of narcolepsy.

<image>Narcolepsy treatment: stimulants, cataplexy medications, sodium oxybate</image>

Section 7: Parasomnias

NREM parasomnias are a group of disorders characterized by abnormal behaviors arising from the deeper stages of non-REM sleep, particularly slow-wave sleep. Sleepwalking involves complex ambulatory behaviors that occur during stage N3 sleep, with the individual performing purposeful-appearing activities while remaining in a state of impaired consciousness and having no subsequent recollection of the events. Sleep terrors present with episodes of intense fear accompanied by dramatic autonomic arousal including screaming, tachycardia, and diaphoresis, yet the individual has no recall of the event the following morning, distinguishing them from nightmares. Confusional arousals manifest as episodes of disorientation and confusion upon awakening from deep sleep, during which the individual may exhibit inappropriate behavior or slowed mentation. Sleep-related eating disorder involves episodes of eating during partial arousals from sleep, often with consumption of unusual or inappropriate food items and amnesia for the events. As a group, NREM parasomnias share several characteristic features: they tend to occur during the first third of the night when slow-wave sleep is most abundant, they typically have their onset in childhood, and they frequently run in families, suggesting a genetic predisposition to incomplete arousal from deep sleep.

REM sleep behavior disorder is a distinct and clinically important parasomnia characterized by the loss of the normal skeletal muscle atonia that accompanies REM sleep, resulting in the physical enactment of dream content. Patients, who are predominantly older men, exhibit vigorous and sometimes violent motor behaviors during REM sleep including punching, kicking, running, and shouting, which frequently result in injury to the patient or bed partner. The dream content associated with these episodes is typically vivid and often involves being chased or attacked, and patients can typically recall the dreams upon awakening, unlike in NREM parasomnias. The most clinically significant aspect of REM sleep behavior disorder is its strong association with the alpha-synucleinopathies, including Parkinson disease, dementia with Lewy bodies, and multiple system atrophy, with longitudinal studies demonstrating that more than 80 percent of patients with idiopathic REM sleep behavior disorder will eventually develop one of these neurodegenerative conditions. Polysomnography demonstrates the pathognomonic finding of REM sleep without atonia, confirming the loss of the normal tonic and phasic muscle inhibition that should accompany REM sleep.

The treatment of parasomnias emphasizes safety measures and addresses identifiable precipitating factors. For NREM parasomnias, the primary interventions include ensuring environmental safety by securing windows, locking doors, and removing potentially dangerous objects from the bedroom, along with low-dose clonazepam for patients with frequent or dangerous episodes, and identification and avoidance of known triggers. Treatment of REM sleep behavior disorder centers on clonazepam, which is effective in reducing the frequency and severity of dream enactment behaviors, and melatonin, which may restore REM atonia through uncertain mechanisms. Safety modifications for REM sleep behavior disorder are critically important and include padding the floor around the bed, securing windows, removing sharp objects and weapons from the bedroom, and in some cases having the bed partner sleep separately until the episodes are controlled. Common triggers for both NREM and REM parasomnias include sleep deprivation, alcohol consumption, and certain medications, and addressing these modifiable factors can substantially reduce episode frequency.

Several additional parasomnias warrant clinical recognition. Nightmare disorder involves recurrent vivid, disturbing dreams that occur during REM sleep and cause significant distress upon awakening, with full recall of the dream content distinguishing nightmares from sleep terrors. Sleep paralysis is the temporary inability to move or speak during the transitions between sleep and wakefulness and may occur as an isolated phenomenon in otherwise healthy individuals or as a component of the narcolepsy symptom complex. Exploding head syndrome is a benign but alarming condition in which the individual perceives a sudden loud noise, such as an explosion or crash, at the onset of sleep, without any accompanying pain. Sleep enuresis, or nocturnal bedwetting, is common in childhood and usually resolves spontaneously but can persist into adulthood in some individuals and may warrant evaluation when it is a new-onset or recurrent symptom.

<image>Parasomnias: NREM disorders, RBD, treatment, other types</image>

Section 8: Restless Legs Syndrome

Restless legs syndrome is diagnosed clinically based on five essential diagnostic criteria that must all be satisfied. The cardinal feature is an urge to move the legs that is typically accompanied by uncomfortable and difficult-to-describe sensations variously reported as creeping, crawling, pulling, or aching. The symptoms characteristically worsen during periods of rest or inactivity, such as when sitting or lying down. Movement, particularly walking, provides temporary relief from the discomfort. The symptoms follow a circadian pattern, worsening during the evening and nighttime hours. Finally, the symptoms must not be better explained by another medical or behavioral condition such as leg cramps, positional discomfort, or habitual foot tapping, and they must cause sufficient distress or impairment to warrant clinical attention.

Several medical conditions are strongly associated with restless legs syndrome and should be systematically evaluated in every patient presenting with symptoms. Iron deficiency is the most important treatable association, and serum ferritin should be checked in all patients, with iron supplementation recommended when levels fall below 75 micrograms per liter, as brain iron stores may be depleted even when peripheral iron indices are only mildly abnormal. Pregnancy is a common precipitant of restless legs syndrome, particularly during the third trimester, with symptoms usually resolving after delivery. End-stage renal disease is strongly associated with restless legs syndrome, with a high prevalence in patients on dialysis. Peripheral neuropathy may coexist with or mimic restless legs syndrome, and its presence should be evaluated in patients with atypical features. Certain medications are well-established exacerbating factors, including selective serotonin reuptake inhibitors, antihistamines, and dopamine antagonists, and a thorough medication review is essential.

Periodic limb movement disorder frequently co-occurs with restless legs syndrome and is characterized by repetitive, stereotyped limb movements during sleep, typically consisting of dorsiflexion of the ankle and flexion of the knee and hip occurring at intervals of 20 to 40 seconds. The periodic limb movement index, which quantifies the number of periodic limb movements per hour of sleep on polysomnography, is used to assess the severity of the condition. Periodic limb movement disorder is frequently found in association with restless legs syndrome, and the two conditions share pathophysiological mechanisms. The clinical significance of periodic limb movements lies in their potential to cause recurrent arousals from sleep, leading to sleep fragmentation and consequent daytime sleepiness that may be the primary presenting complaint.

The treatment of restless legs syndrome follows a stepwise approach that begins with correction of underlying causes and progresses to pharmacological therapy. Iron supplementation is the first step when the serum ferritin is below 75, with intravenous iron considered when oral supplementation is insufficient or not absorbed adequately. Alpha-2-delta ligands, specifically gabapentin and pregabalin, are now considered first-line pharmacological treatment for restless legs syndrome due to their efficacy and favorable long-term safety profile compared with dopaminergic agents. Dopamine agonists, including pramipexole and ropinirole, are effective for symptom relief but carry the significant risk of augmentation, a paradoxical worsening of symptoms characterized by earlier onset in the day, spread to the upper extremities, and increased intensity, which develops in a substantial proportion of patients with chronic use and should be carefully monitored. Opioids may be considered for refractory cases that have failed other therapies. Augmentation remains the most important long-term management challenge, and when it develops with dopamine agonists, the offending agent should be gradually tapered and the patient transitioned to an alternative medication class.

<image>Restless legs syndrome: criteria, associations, PLMD, treatment</image>

Section 9: Circadian Rhythm Disorders

Circadian rhythm sleep-wake disorders encompass a group of conditions resulting from misalignment between the endogenous circadian clock and the desired or socially required sleep-wake schedule. Delayed sleep phase disorder is the most common circadian rhythm disorder and is characterized by a habitual sleep onset that is delayed well beyond conventional bedtime, with corresponding difficulty waking at the required morning hour. Advanced sleep phase disorder presents as the opposite pattern, with early evening sleepiness and early morning awakening. Shift work disorder develops in individuals whose work schedule requires them to be active during their biological night, resulting in insomnia during the designated sleep period and excessive sleepiness during the work shift. Jet lag disorder is a temporary condition that arises when rapid travel across time zones creates an acute mismatch between the internal circadian clock and the environmental light-dark cycle. Non-24-hour sleep-wake rhythm disorder, also called free-running disorder, occurs when the circadian period is not entrained to the 24-hour day and the sleep-wake cycle progressively shifts later each day, a condition most commonly seen in totally blind individuals who lack the photic input necessary for circadian entrainment. Irregular sleep-wake rhythm disorder is characterized by the absence of a clearly defined circadian pattern, with sleep distributed across multiple periods throughout the 24-hour day, and is most commonly associated with neurodegenerative diseases such as dementia.

Delayed sleep phase disorder is particularly prevalent in adolescents and young adults, in whom the combination of an inherent biological tendency toward later circadian timing and social and behavioral factors that reinforce late sleep onset creates a significant clinical problem. The typical pattern involves habitual sleep onset at 2 AM or later with a corresponding inability to wake at the time required for school or work, leading to chronic sleep deprivation on weekdays and compensatory oversleeping on weekends. The primary clinical problem is not the quality or quantity of sleep itself, which is normal when the patient sleeps on their preferred schedule, but rather the conflict between the endogenous circadian preference and social or occupational obligations. Diagnosis relies on a consistent pattern documented by sleep diary and actigraphy over at least two weeks, demonstrating the characteristic delayed but stable sleep-wake timing.

Treatment of circadian rhythm disorders leverages the known physiological responses to light and melatonin to shift circadian timing in the desired direction. Morning bright light therapy is the primary intervention for delayed sleep phase disorder, as light exposure in the early morning advances the circadian clock, promoting earlier sleep onset on subsequent nights. Conversely, evening light exposure is used for advanced sleep phase disorder to delay the circadian clock and postpone sleep onset. Exogenous melatonin, when timed appropriately relative to the endogenous circadian phase, provides an additional phase-shifting signal. Chronotherapy involves gradual, progressive shifting of the sleep-wake schedule in the desired direction over successive days. Consistent sleep hygiene, particularly maintaining a regular schedule including on weekends, is foundational. For shift work disorder, strategic napping before or during the shift and timed light exposure during the work period help maintain alertness and reduce the risk of errors.

Melatonin is a versatile therapeutic tool in the management of circadian rhythm disorders, with its timing of administration being more important than the dose for achieving the desired circadian phase-shifting effect. For delayed sleep phase disorder, melatonin should be administered 3 to 5 hours before the desired sleep onset to advance the circadian clock, with the earlier timing within this window providing a stronger phase-advancing effect. For jet lag disorder, melatonin is taken at the desired bedtime at the destination to help resynchronize the circadian clock with the new time zone. Effective doses range from 0.5 to 5 milligrams, and lower doses are often as effective as higher doses for circadian phase shifting, since the chronobiotic effect of melatonin is mediated through specific receptor activation rather than a dose-dependent sedative mechanism. Melatonin is generally well tolerated, with minimal side effects and no significant potential for dependence or withdrawal.

<image>Circadian disorders: types, delayed phase, treatment, melatonin</image>

Section 10: Insomnia

Chronic insomnia disorder is defined by a specific set of diagnostic criteria that distinguish it from the transient sleep difficulties experienced by most people at some point in their lives. The patient must report difficulty with initiating sleep, maintaining sleep with frequent awakenings, or early morning awakening with an inability to return to sleep. These difficulties must occur despite adequate opportunity and circumstances for sleep, meaning that the patient has sufficient time allocated for sleep in a suitable environment. The sleep disturbance must produce daytime impairment, which may manifest as fatigue, mood disturbance, difficulty with concentration, or impaired occupational or social functioning. To meet the threshold for chronic insomnia, the symptoms must be present for at least three nights per week and persist for at least three months.

Insomnia can be further characterized by the predominant pattern of sleep disruption, which often provides clues to the underlying pathophysiology. Sleep-onset insomnia, characterized by difficulty falling asleep at the beginning of the night, is commonly associated with anxiety, hyperarousal, or circadian misalignment. Sleep-maintenance insomnia, in which the patient falls asleep initially but experiences frequent awakenings during the night with difficulty returning to sleep, may be associated with medical conditions, pain, sleep-disordered breathing, or mood disorders. Early morning awakening, in which the patient wakes well before the desired time and cannot return to sleep, is a pattern frequently associated with depression. Comorbid insomnia occurs in the context of psychiatric disorders, medical conditions, or other sleep disorders, and recognizing and treating the comorbid condition is an important component of management, though the insomnia itself often requires direct treatment as well.

Cognitive behavioral therapy for insomnia, known as CBT-I, is the recommended first-line treatment for chronic insomnia and has been shown to be more effective than pharmacotherapy in the long term. Sleep restriction therapy, a core component of CBT-I, involves limiting the time spent in bed to match the patient's actual sleep duration, thereby increasing sleep drive and consolidating sleep into a more efficient period. Stimulus control therapy aims to strengthen the association between the bed and sleep by instructing patients to use the bed only for sleep and sexual activity, to go to bed only when sleepy, and to leave the bed if unable to sleep within 15 to 20 minutes. Cognitive therapy addresses the dysfunctional beliefs and catastrophic thinking about sleep that perpetuate insomnia, such as unrealistic expectations about sleep duration or excessive worry about the consequences of poor sleep. Sleep hygiene education addresses environmental and behavioral factors including bedroom temperature, light, and noise, as well as the timing of exercise, caffeine, and meals. Relaxation techniques, including progressive muscle relaxation and mindfulness-based strategies, help reduce the physiological and cognitive arousal that impedes sleep onset.

Pharmacotherapy for insomnia is generally reserved for patients who have not responded adequately to CBT-I or who require short-term relief while behavioral interventions take effect. Benzodiazepines such as temazepam are effective for short-term use but carry significant risks of dependence, tolerance, and withdrawal, limiting their role to brief courses. Non-benzodiazepine hypnotics, the so-called Z-drugs including zolpidem and eszopiclone, act on the same GABA-A receptor but with more selective binding profiles; they share many of the same concerns regarding dependence and complex sleep-related behaviors. Melatonin receptor agonists, specifically ramelteon, target the melatonin MT1 and MT2 receptors and are primarily effective for sleep-onset insomnia without abuse potential. Dual orexin receptor antagonists, including suvorexant and lemborexant, represent a newer pharmacological class that promotes sleep by blocking the wake-promoting orexin signaling system and are effective for both sleep-onset and sleep-maintenance insomnia. Low-dose trazodone, a sedating antidepressant, is widely used off-label for insomnia due to its sedative properties, low cost, and low abuse potential. Benzodiazepines should be avoided for long-term use, particularly in elderly patients, due to increased risks of falls, cognitive impairment, and confusion.

<image>Insomnia: definition, types, CBT-I, pharmacotherapy</image>

Summary

• Sleep stages: N1 (light), N2 (spindles, K-complexes), N3 (slow-wave), REM (dreams, atonia)
• OSA: snoring, witnessed apneas, daytime sleepiness; AHI ≥5; CPAP first-line
• Central sleep apnea: no respiratory effort; Cheyne-Stokes with heart failure
• Narcolepsy Type 1: EDS + cataplexy; low CSF orexin; MSLT shows SOREMPs
• Narcolepsy treatment: modafinil for sleepiness; sodium oxybate for cataplexy
• REM sleep behavior disorder: acts out dreams; older men; high risk for α-synucleinopathy
• RLS: urge to move legs, worse at rest and evening; gabapentin first-line; check ferritin
• Circadian disorders: light therapy and melatonin timed appropriately
• CBT-I: first-line for chronic insomnia; sleep restriction, stimulus control
• Avoid benzodiazepines long-term: especially in elderly; falls, cognitive impairment

Key Terms

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