Michael J. Howell and Carlos H. Schenck

Overview

Parasomnias are abnormal physical and experiential phenomena that arise from the sleep period. Disorders of arousal, such as sleepwalking, result from an incomplete dissociation of wakefulness from non–rapid eye movement (NREM) sleep. Conditions that provoke repeated cortical arousals or that promote sleep inertia lead to NREM parasomnias by impairing normal arousal mechanisms. Sleep-related eating disorder (SRED) is characterized by a disruption of the nocturnal fast with episodes of feeding after an arousal from sleep. NREM parasomnias are often associated with the use of sedative hypnotic medications, in particular the widely prescribed benzodiazepine receptor agonists (BRAs). Recently, evidence suggests that many cases of sleepwalking and SRED are induced when BRAs are mistakenly prescribed to patients with restless legs syndrome (RLS). REM sleep behavior disorder (RBD) is characterized by a loss of skeletal muscle paralysis during REM sleep that leads to potentially injurious dream enactment. The loss of REM atonia in RBD is often a cardinal finding in the development of α-synuclein neurodegenerative disorders such as Parkinson disease. Epilepsy with motor seizures may be limited to the nocturnal period and may thus be confused with disorders of arousal and RBD. Other parasomnias include experiential phenomena, such as “exploding head” syndrome and sleep-related hallucinations (see Table 12-1 and Box 12-1).

Pathophysiology of Parasomnias

The current understanding of the underlying pathophysiology of parasomnias is based on the understanding that sleep and wakefulness are not mutually exclusive states of being. As one falls asleep and advances through the various sleep stages, the sleep stage shifts are not complete “on or off” switch phenomena, but rather involve transitions of several neuronal centers for an equivocal stage to declare itself. It is during this period of sleep-wake dissociation that a person can encounter an admixture of different states of being. They may overlap or intrude into one another and result in complex behaviors (Fig. 12-1).

Another hypothesis is that central pattern generators (CPGs), as illustrated in Figure 12-2, lead to deafferentation of the locomotor centers from the generators of the different sleep states. Locomotor centers are present at both spinal and supraspinal levels, and this dissociation can explain motor activity or ambulation, especially in patients with disorders of arousals.

CPGs are located in the brainstem and spinal cord and are believed to be responsible for involuntary motor manifestations classified into 1) oroalimentary automatisms, bruxism, and biting; 2) ambulatory behaviors that range from the classical bimanual-bipedal activity of somnambulism to periodic leg movements; and 3) various sleep-related events associated with fear, such as sleep terrors, nightmares, and violent behaviors.

Disorders of Arousal: Non–Rapid Eye Movement Parasomnias

The NREM parasomnias include confusional arousals, sleepwalking, and sleep terrors and represent dissociated states of being. Brain regions that coordinate motor and visual function are wakeful, but those areas of the cortex that lead to executive function and memory linger in sleep. These disorders of arousal are common in children and occur in up to 1% to 4% of adults, with most adults describing parasomnias persisting from childhood.

The disorders of arousal vary across a spectrum of duration, autonomic activity, and arousal threshold. Confusional arousals are characterized by disoriented behavior limited to the sleeping area with subsequent impaired recall of events (see Figs. 12-3 and 12-4 and Video 12-1). In adults, they can sometimes be triggered by a comorbid sleep disorder such as obstructive sleep apnea (OSA, Fig. 12-5). Sleepwalking is a combination of ambulation with impaired consciousness (Figs. 12-6 and 12-7). Sleep terrors usually occur in preadolescent children, involve episodes of intense fear initiated by a sudden loud vocalization, and are accompanied by precipitously increased autonomic nervous system activity (Figs. 12-8 through 12-10). Patients with sleep terrors are typically inconsolable. The major differences between sleep terrors and REM nightmares are shown in Table 12-2.

NREM parasomnia patients are often difficult to awaken during an event; if awakened, they are usually confused and disoriented and have amnesia for any mental activity preceding the arousal.

Comorbid conditions that promote sleep inertia or fragmented sleep lead to incomplete cortical arousal. Phenomena that deepen sleep, such as sleep deprivation and sedative medications, promote NREM parasomnias by impairing arousal mechanisms (Clinical Case 12-1). Conditions that cause repeated cortical arousals, such as sleep-disordered breathing (see Fig. 12-5) or noise, lead to parasomnias through increased sleep fragmentation. The isolated activation of functional groups of motor neurons with a relative paucity of activity in brain regions that control executive function and memory account for the poor judgment and amnesia that characterize NREM parasomnias.