Parasomnias 

Parasomnias are disorders characterized by undesirable motor, verbal, or experiential phenomenon occurring in association with sleep, specific stages of sleep, or sleep-awake transition phases.^[1] Parasomnias may be categorized as (1) primary parasomnias, which are disorders of sleep states and are further classified according to the sleep state of origin, rapid eye movement (REM) or non–rapid eye movement (NREM) or (2) secondary parasomnias, which are disorders of other organ systems that may manifest during sleep, such as nocturnal epilepsy, respiratory dyskinesias, arrhythmias, and gastroesophageal reflux.

Two major types of primary sleep disorders are dyssomnias and parasomnias. Primary sleep disorder is a malady of sleep that does not appear to be secondary to a physical or mental illness and is not substance-induced. Unlike dyssomnias, which are characterized by abnormal sleep quality, including initiation, maintenance, duration, timing, and amount of sleep, parasomnias are distinguished by deviant behavioral and/or physiologic events. These abnormalities/events are reliably associated with either the sleep/wake interface or certain sleep stages. Additionally, parasomnias manifest by activation of systems, such as the autonomic nervous system, or programs, such as cognitive, behavioral, or motor program stimulation.^{[2, 3]}

The parasomnias have been subdivided according to 2 major classification schemes, the American Psychiatric Association's Diagnostic Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) and the American Sleep Disorders Association's International Classification of Sleep Disorders (ICSD).^{[4, 5, 6, 1]} Four major types of parasomnias are included in the DSM-IV-TR. They include (1) nightmare disorder, (2) sleep terror disorder, (3) sleepwalking disorder, and (4) parasomnias not otherwise specified. However, the DSM-V is projecting the reclassification of parasomnias into Disorders of Arousal to include: sleepwalking, sleep terror, and confusional arousals.^[7] The ICSD subdivides the parasomnias into 3 groups according to the sleep state of origin. They include (1) REM, (2) NREM, and (3) miscellaneous (ie, not respecting the sleep state).

The 5 disorders that are primarily discussed in this article are nightmare disorder, sleep terror disorder, sleepwalking disorder, REM sleep behavior disorder, restless legs syndrome (RLS), and periodic limb movement disorder (PLMD).

• Nightmare disorder: Also called dream anxiety attacks, these events typically occur during the latter third part of the night, usually during REM sleep, but do not involve any motoric dream enactment. They may be associated with tachycardia, tachypnea, diaphoresis, and arousal. Complete alertness and subsequent recollection of the dreams differentiates nightmares from sleep terrors. Note that nightmares are another form of dreams except with documented emotional and physiological consequences often invoking anger and embarrassment, but most often fear.^{[8, 3]}
• Sleep terror disorder: Sleep terror is a disorder of arousal that primarily occurs during stages III and IV of NREM sleep. Sleep terror manifests as extreme panic and a loud scream during sleep, followed by motor activities such as hitting objects or moving in and out of the bedroom. Subsequent recollection of these episodes either does not occur or is partial.^{[3, 9, 10]}
• Sleepwalking disorder: Again, this disorder arises from slow-wave stages of NREM sleep. The subject performs complex automatic behaviors, such as wandering aimlessly, carrying objects, going outdoors, and performing other activities of varying complexity and duration.^{[3, 9, 11]}
• REM sleep behavior disorder: REM sleep behavior disorder is dream-enacting behavior that includes talking, yelling, punching, kicking, sitting, jumping out of bed, arm flailing, and grabbing. An acute form may occur during withdrawal from ethanol or sedative-hypnotic drugs. The chronic form presents for evaluation following observations of bed partners.^{[3, 12, 13]}
• Restless legs syndrome (RLS) and periodic limb movement disorder (PLMD): These are common disorders that often coexist. RLS primarily presents as insomnia, whereas PLMD is a well-recognized cause of excessive daytime somnolence. Nearly all patients with RLS have periodic limb movements, but this is not the case vice versa. These disorders are not classified officially by the DSM-IV-TR as parasomnias. RLS and PLMD can be differentiated from parasomnias by their stereotyped nature.^{[14, 15, 16, 17, 18]}

Two parasomnias recently validated and more extensively described in the literature are (1) somnambulistic sexual behavior, or sexsomnia, and (2) sleep-related eating disorder.

Sexual behaviors of all types may occur during sleepwalking. Somnambulistic sexual behavior (also called sexsomnia, sleep sex) is considered a variant of sleepwalking disorder. Prior assumptions concluded sexsomnia occurred in individuals just acting out their dreams as a consequence of an underlying psychological condition; however, such theories have been debunked. Sexual behavior during a sleep automatism can vary from explicit sexual vocalizations, to violent masturbation, to complex sexual acts including fondling, cunnilingus, fellatio, and even vaginal and anal sex.

Features of this condition are analogous to other NREM parasomnias that occur during what is known as a confusional arousal during the deeper stages of sleep. Throughout this time, the brain is in a hybridized state in which cortical areas (controlling higher thought processing and reasoning) are deactivated and more primitive functions (such as eating and sex) remain active. Individuals are typically amnestic for the episode. Those who commit these sexual acts typically have a family or personal history of other parasomnias.

Medicolegal issues have occurred in a small number of cases, though the actual forensic implications at present are nebulous. There are some similarities known among several of the cases: involvement of a male perpetrator under the age of 35, accusation of sexual assault/rape, claims of amnesia following the event, and a history of prolonged complex somnambulism. This behavior is more common than previously thought because a significant number of patients with this unusual parasomnia behavior were identified only after specific questions were asked.^{[19, 20]}

The literature describes 2 disorders involving the consumption of food during the night/bedtime: SRED (sleep-related eating disorder) and NES (night-eating syndrome). A clear distinction should be drawn between the 2 since NES is not categorized as a parasomnia due to maintenance of full consciousness during the episodes. Although first described by Stunkard et al in 1955, no uniform definition of NES has yet been adopted. This disorder is depicted by consumption of excessive amounts of food either before bed or during nocturnal awakenings. It is up to 4 times more common in females and tends have an onset in late adolescence.^{[21, 22]}

The current definition focuses on NES to be present if patients report the following: (1) skipping breakfast ≥ 4 d/wk, interpreted as morning anorexia; (2) consuming more than 50% of total daily calories after 7 pm; and (3) difficulty falling asleep or staying asleep ≥ 4 d/wk. Whether night-eating syndrome should be differentiated from nocturnal eating syndrome is not clear in the literature. However, the terms may be defined distinctly as (1) night eating syndrome (defined as morning anorexia, evening hyperphagia, and insomnia) and (2) nocturnal eating syndrome (defined as eating at night after having gone to bed).^[23]

On the other hand, SRED can be conceptualized as a binge eating disorder incorporated with disordered arousal, confusional behavior, and amnesia of a non-REM parasomnia. Episodes often occur within the first 2-3 hours of sleep with ingestions of often high carbohydrate foods in a hurried, uncontrollable manner. Contrary to other non-REM parasomnias, a fluctuation in level of awareness exists between episodes within the same night. Interestingly, there is relatively high comorbidity with RLS.^[24]

Case study

Mr. A is a 28-year-old veteran of combat in Afghanistan. He was engaged at one juncture in hand-to-hand combat with guerilla fighters; although he escaped, many of his unit were killed before his eyes. Since returning home, he has suffered from multiple symptoms of posttraumatic stress disorder, particularly nightmares. Six months ago, he had one of his recurring dreams about strangling an enemy combatant. When he awoke, his wife was dead in bed beside him. He had strangled her in his sleep.

Human life encompasses 3 completely different states of existence: wakefulness, REM sleep, and NREM sleep. Sleep is not simply the passive absence of wakefulness; it is an extensive reorganization of CNS activities occurring during sleep. Each state of being is controlled by its unique neuroanatomic, neurophysiologic, and neurochemical association.^{[3, 25]}

Wakefulness and REM and NREM sleep states overlap as transition occurs from one state to another. A large number of neural networks, neurotransmitters, and neurochemicals must be recruited concurrently to assert a given state of existence. Dissociation of these states and the admixture of state-determining variables are the mechanisms that set primary sleep parasomnias in motion. For example, intrusion of NREM sleep during wakefulness may produce sleep drunkenness or microsleeps; occurrence of REM sleep during wakefulness generates cataplexy or wakeful dreaming; loss of muscle atonia during REM sleep sets off acting out of dreams, termed REM behavior disorder.^{[26, 25]}

The pathophysiology of parasomnias is unknown, although considerable speculation exists about the role of various functional systems in each disorder. Abnormalities in the normal regulation of different phases of sleep may be present. Disorders of arousal have been theorized to involve the relative deactivation of the frontal lobe and inappropriate activation of the limbic areas. Some disorders, such as sleep terror and sleepwalking disorders, are primarily disturbances of slow-wave sleep, whereas sleep paralysis and REM behavior disorders are those of REM sleep.

Some studies suggest that sleep deprivation and forced arousals during slow-wave sleep can induce somnambulistic episodes in predisposed adults. Other conditions, such as rhythmic movement disorder (eg, head banging) are those of sleep-wake transition. Because the pattern of activation of parasomnias may resemble epilepsy (abrupt onset, confusion, disorientation, and amnesia for the event period), parasomnias were originally considered a form of epilepsy. Gastaut and Broughton's elegant work in 1965 and Broughton's work published in 1968 established the nonepileptic nature of parasomnias.^{[27, 25, 28]}

Rapid eye movement sleep behavior disorder

The physiologic phenomena that occur during REM sleep can be categorized as tonic and phasic. Tonic phenomena appear throughout an REM period. Examples include electromyographic (EMG) suppression and low-voltage electroencephalography (EEG). The phasic phenomena occur intermittently during an REM period. Examples include rapid eye movements and variability of cardiac cycle and respiratory function.^[29]

The tonic and phasic processes have been observed to be variously dissociated and recombined across different states. In contrast to wakefulness, which is characterized by consciousness and muscle tone, REM sleep is associated with dreaming and muscle atonia. Generalized atonia of REM sleep probably is caused by active inhibition of motor activity by centers identified to be present in the pons. REM sleep behavior can be experimentally produced in cats by bilateral pontine tegmental lesions, which are associated with the absence of REM atonia. However, in humans, a structural neuropathology is not necessary for REM behavior disorder because most patients do not have an identifiable neurological disorder. Therefore, functional dysregulation by depression of brainstem structures is responsible for atonia. The reduced activity of structures responsible for inhibiting phasic activity in the brain stem further contributes to the clinical manifestations of REM sleep behavior disorder.

Restless legs syndrome and periodic limb movement disorder

RLS and PLMD may be 2 clinical manifestations of the same CNS dysfunction. The neurophysiological mechanisms responsible for these disorders are not well described. PLMD occurs with a striking periodicity, suggesting that an underlying CNS pacemaker may be operative. Several observations have suggested that PLMD likely originates in the subcortical region and is regulated by rhythmic fluctuations at the brainstem level.^[30]

Both of these disorders may be the behavioral manifestation of CNS processes that become disinhibited. Patients with these disorders also may have a lower arousal threshold. Polysomnographic recordings exhibit periodic arousing stimuli leading to K complexes, followed by alpha activity, and then leg movements. The neuropharmacological hypothesis supports that an impaired CNS dopaminergic mechanism also may be involved. The deficiency of dopamine binding sites or low concentrations of dopamine and homovanillic acid have been found in several populations who have PLMD.^[31]

Restless legs syndrome pathology involves the CNS rather than the peripheral nervous system. CNS involvement in restless legs syndrome is based in the subcortical or brainstem areas of the brain rather than the spinal system. Since clinical evidence clearly points to the responsiveness of restless legs syndrome to administration of dopamine or dopamine agonists, abnormality of this system likely is responsible for restless legs syndrome and periodic limb movement disorder.

Various conditions commonly associated with secondary RLS, such as end-stage renal disease, pregnancy, and gastric surgery, are associated with iron insufficiency. These conditions make it difficult for the brain to access iron sufficiently for proper functioning. Iron is stored and transported in the form of ferritin; transferrin transports iron into the cells through the transferrin receptor. When iron is low, ferritin is decreased, but transferrin levels are increased. Cerebrospinal fluid (CSF) and serum from patients with RLS have lower CSF ferritin levels and higher CSF transferrin levels. Low ferritin levels correlated with restless legs syndrome severity. Furthermore, a connection may exist between iron insufficiency and dopamine pathology in RLS.

Single-photon emission computed tomography (SPECT) studies of the brain have identified defects in striatal dopamine D2 receptors. Other studies have pointed out an abnormality of the endogenous opioid system and abnormalities in iron metabolism with ferritin deficiency. Recent studies have reported low tissue iron content in substantia nigra and red nuclei on brain MRI scans of restless legs syndrome patients. Consequently, interactions between the opioid and dopamine systems that occur in the basal ganglia, brainstem, and spinal cord contribute to the genesis of RLS and PLMD.^[29]

Frequency

United States

• Nightmare disorder: Of children aged 3-5 years, 10-50% may have this disorder. The prevalence in adults is unknown, although up to 50% of adults report occasional nightmares, and perhaps 5-8% experience recurring nightmares.^[32]
• Sleep terror disorder: Information regarding frequency is limited at best. The DSM-IV-TR estimates the prevalence rate to be 1-6% in children and less than 1% in adults.^[32]
• Sleepwalking disorder: The criterion-based disorder is estimated to occur in 5% of children, but episodes of the disorder have been documented in as many as 30% of clinical samples of children. The highest prevalence of this condition is between the ages of 3 and 10. Some clinical samples have shown upwards of 7% in adults, though approximately 80% of these cases are a continuation of childhood behavior.^[32]
• REM sleep behavior disorder: This disorder may be rare; however, because many other sleep disorders, in particular the other parasomnias, may be misdiagnosed as REM sleep behavior disorder, the true prevalence is not known. It is diagnosed most often in the sixth or seventh decade of life. This disorder is often familial. As many as 60% of patients presenting to sleep clinics may have a positive family history.^[4] Men and women are affected equally. Although not proven, autosomal dominant transmission is expected. A telephone survey has shown an overall prevalence rate of violent behaviors during sleep of 2%, approximately one quarter of these likely were REM sleep behavior disorder, indicating that REM sleep behavior disorder has an overall prevalence rate of 0.5%.^{[33, 34, 35]}
• RLS and PLMD: The prevalence rate of RLS is estimated to be as high as 10% in the general population and increases with age. The prevalence of PLMD also increases with age; 5% of the population aged 30-50 years has PLMD, compared to 30% of the population older than 50 years and 40% of the population older than 65 years. PLMD has been reported to be responsible for insomnia in 17% of patients and hypersomnia in 11% of patients evaluated at sleep disorder clinics.^{[36, 35]}

International

The prevalence rates are not known to be any different from US rates.

Mortality/Morbidity

• The death rate of these 3 parasomnias is quite low; few, if any, reliable statistics exist regarding mortality. Similarly, the morbidity associated with the parasomnias mostly is secondary, such as the consequences of sleepwalking, assaulting others while asleep, and sleep deprivation in caretakers.
• One specific morbidity issue is eating behavior associated with sleepwalking. The associated morbidity primarily relates to excessive food intake.
• Of note is the inclusion of 2 parasomnias in the ICSD, the hallmark of which is death. The first is sudden unexplained nocturnal death syndrome, which is most common in otherwise healthy young adults of Southeast Asian descent, such as Laotian, Kampuchean, and Vietnamese people. The other is the better-known sudden infant death syndrome.

Race

• Information regarding the racial distribution of parasomnias is not available.

Sex

• Women report nightmares more frequently, in a ratio of 2-4:1.
• Among children, sleep terror disorder is more prevalent in boys than in girls, but in adults, the ratio is even.
• Sleepwalking disorder occurs with equal frequency in both sexes.
• REM sleep behavior disorder is more prevalent in males, but the exact ratio is not known.
• The prevalence of RLS and PLMD is similar between men and women.

Age

• See Frequency for the differences in age distributions of the parasomnias.