Sleepwalking

Epidemiology and Clinical Features

Sleepwalking is not uncommon, as up to 40% of normal children sleepwalk at least once in their lives, with 2 to 3% experiencing recurrent episodes with a frequency of at least once per month.⁹ Both sexes are equally affected,¹⁰ and onset of sleepwalking peaks at approximately 5 years of age,⁹ with most episodes subsiding by the teenage years.¹⁰ This may reflect the decrease in amount of SWS with age as well as maturation of the nervous system, which in turn reduces the likelihood of partial arousals.¹¹ In children who sleepwalk, daytime functioning is usually normal, and psychologic tests demonstrate no consistent psychopathology in most of these individuals.⁹ However, while sleepwalking is often considered a disorder of childhood, this parasomnia may be more common in adults than previously thought, with a prevalence of 4%.¹² Furthermore, in adults, sleepwalking may occur nearly three times more often per year and persist for a longer period of time than in children.⁹

Clinically, the sleepwalker may exhibit calm or agitated behavior, which may overlap with confusional arousals or sleep terrors,¹⁰ two other NREM parasomnias. The sleepwalker may behave as if without judgment or purpose (eg, climbing out a bedroom window or wandering outside), or may carry out relatively complex behaviors (eg, carrying objects, moving furniture, vocalizing, eating, or even driving a car).^10,12 However, movements are generally clumsy and result in tripping or falling; similarly, misperceptions of the environment may also lead to injury (eg, walking though a glass door).¹⁰ Alternatively, sleepwalkers may exhibit aggressive behavior, such as wielding weapons or other dangerous objects.¹² As in sleep terrors, the eyes are usually wide open and have a glassy stare, but communication is usually impossible¹²; further agitation may result from attempts at restraint by others.¹²

In children, the timing of sleepwalking behavior may serve as a clue to the diagnosis, as well as assist in treatment (as will be discussed). Episodes usually begin 15 to 20 min after sleep onset, and the duration of episodes may vary from 1 min to half an hour.^10,12 Sleepwalkers usually return to bed spontaneously or under gentle guidance.¹⁰ While older children and adults may awaken fully,¹⁰ most often there is no recollection of the episode.¹⁰ Sleepwalking in adults may occur at any time during the night,¹² and is often associated with stress or major life events.⁹ Furthermore, episodes in adults may take the form of "specialized" behaviors, such as sleep-related eating and sleep-related sexual activity--without conscious awareness.¹² Although there is usually no recollection of the event, vivid dreamlike mentation may occasionally be experienced.¹³ While it was believed in the past that persistence beyond childhood or the development of sleepwalking in adulthood was an indication of significant psychopathology, this has been shown to be unfounded.¹² However, onset of sleepwalking in the elderly is uncommon and is usually a manifestation of another disorder, such as delirium, drug toxicity, or seizure disorder.⁹

Pathophysiologic Basis for Treatment

The exact pathophysiology behind sleepwalking is incompletely understood. However, it is clear that sleepwalking tends to occur near the end of SWS, and is also known as an "SWS parasomnia." Furthermore, sleepwalking--like confusional arousals and sleep terrors--is thought to result from "state dissociations" in which the transition from one state to another is incomplete. The individual becomes "trapped" in a state that incorporates features of both sleep and wakefulness, rather than fully awakening or transitioning to another stage of sleep.^6,10 As illustrated in Figure 1, such state dissociations may also explain many of the features of narcolepsy, as well as RBD. As sleepwalking represents dissociation between NREM sleep and wakefulness, it is also referred to as a disorder of arousal or partial arousal (Table 1). While such errors in state transitions occur commonly, the development of parasomnic behavior ultimately depends on not only SWS pressure, but also intervening SWS arousal enhancement or disruption.¹⁴ Specifically, genetic, endogenous, and exogenous (environmental) factors are involved in the generation of disorders of partial arousal. As shown in Figure 1, three major factors determine the occurrence of clinically important partial arousals: tonic sleep factors (background susceptibility present throughout the entire sleep period), phasic sleep factors (intrinsic or extrinsic triggers for arousal), and the behavioral response of the individual.^8,15 This model may also provide a framework upon which therapy can be devised.

Among the tonic factors, genetic and developmental factors are the most important. The presence of genetic factors is supported by the common history of sleepwalking in one or both parents of sleepwalkers,¹⁰ and in twin studies.¹⁶ Partial arousals are most common in young children because their SWS is deeper and longer than in older children and adults. Another important tonic sleep factor that affects the depth and duration of SWS is sleep deprivation,¹⁷ which may be related to behavioral sleep disorders.¹⁸ This, along with other causes of sleep deprivation--such as an irregular sleep schedule, staying up late, or forgoing a daily nap--may increase a child's homeostatic NREM and SWS pressure.¹⁸ The single factor most commonly associated with arousal parasomnias in childhood may be that of being "overtired," typically from sleep deprivation or an unusually active day.¹⁸ Drugs and psychological factors may also play a role in contributing to increased SWS pressure. ¹⁷ Finally, individuals may also be predisposed to such behavior if they have an underlying instability of SWS, revealed only with the delineation of microstructural abnormalities in the sleep EEG, reflected by an increased rate of the cyclic alternating (EEG) pattern (CAP) and increased number of CAP cycles.^6,20 The increase in such NREM sleep instability and arousal oscillation may predispose one to subsequent triggering of abnormal motor episodes during sleep.⁶

While sleepwalking can occur spontaneously in the majority of children based on these underlying tonic factors,¹⁷ such partial arousals may also be triggered or precipitated by any form of endogenous or exogenous stimulation. These are what constitute the phasic factors, which, when strategically timed, may result in partial arousals and parasomnic behavior.^11,17 In fact, sleepwalking can be induced by standing a child up or by sounding a buzzer during SWS.²¹ Among possible endogenous phasic factors are comorbid medical conditions, including febrile illnesses and seizures, or psychological stress¹¹; psychological factors may therefore serve as both tonic and phasic factors in the development of sleepwalking. Disorders of arousal may be exacerbated by pregnancy or menstruation, suggesting hormonal factors.¹¹ Importantly, concurrent physiologic sleep disorders such as SRBD/UARS or PLMD may also trigger partial arousals. Sleep-disordered breathing may provoke any type of parasomnia, and should always be considered when frequent nocturnal events or unrefreshing sleep are reported.¹¹ In this situation, although the observed clinical phenomenon may be sleepwalking, the more significant underlying sleep disorder may be sleep apnea. It is notable that nine types of parasomnias related to sleep-disordered breathing have been identified⁸ (Table 2), three of which involve SWS parasomnias (listed in Figure 1). Two relate specifically to sleepwalking: obstructive sleep apnea-induced confusional arousals from NREM sleep with complex or violent behaviors that resemble sleepwalking, and SWS rebound related to use of nasal continuous positive airway pressure that results in sleepwalking. PLMS, including those related to PLMD, may similarly trigger partial arousals,²² and may also coexist with other sleep disorders, such as SRBD and narcolepsy, resulting in significant fragmentation of sleep.¹¹

In addition to increasing SWS pressure, medications , like psychological factors, may also act as phasic factors in sleepwalking. Sedative or hypnotic agents (including zolpidem 23 in the setting of acoustic perturbation), neuroleptics, lithium, minor tranquilizers, and stimulants and antihistamines (often taken in combination) may help to trigger sleepwalking.^8,10 Accordingly, drug-induced sleep disruption should be considered in any child who exhibits arousal disorders either during or shortly after the use of psychotropic or sedative medications.¹¹ Similarly, reactions to medications should also be considered in the elderly.⁹ Finally, the ultimate behavioral response to the partial arousal is determined by developmental and psychological factors as well as by drugs.¹⁷ Medications such as benzodiazepines that are used to symptomatically suppress parasomnic behaviors act not only by reducing SWS, but also by muting motor activity and thus witnessed behavior.