Overview of the parasomnias


What are parasomnias?  1

What are the social and economic costs of parasomnias?  2

What are REM sleep parasomnias?  3

Nightmare disorder   3

Recurrent isolated sleep paralysis  5

REM sleep behavior disorder   6

What are NREM sleep parasomnias?  8

Confusional arousals  8

Sleepwalking (somnambulism) 9

Sleep terrors  9

What other parasomnias are there?  10

Sleep enuresis  10

Sleep-related bruxism    11

Sleep-related rhythmic movement disorder   11

Somniloquy   12

Sleep-related groaning   14

References  15


What are parasomnias?

The American Academy of Sleep Medicine defines parasomnias as “undesirable physical events or experiences that occur during entry into sleep, within sleep or during arousals from sleep”.1 They are varied in their expression, ranging from simple movements (rocking, grinding, and groaning) to complex, seemingly purposeful behaviors (sleepwalking, REM behavior disorder). Most parasomnias are considered to be normal sleep phenomena and benign, especially when they occur in children. The incidence and prevalence of these undesirable sleep events decreases significantly with the onset of adolescence. In some cases they can lead to injuries, psychological distress and sleep disturbances for both the individual and family members. In legal cases of sleep-related violence (when a diagnosis of parasomnia has been established), parasomnias involve behaviors that are not clearly motivated, are devoid of sound judgment and not under conscious deliberate control.

Parasomnias include many conditions with different pathophysiologies and responses to treatment. They are currently classified into primary parasomnias, which are disorders of sleep states per se, and secondary parasomnias, which are disorders of specific organ systems that manifest preferentially during sleep.  Primary parasomnias are further classified into 1) disorders associated with NREM [non-REM] sleep (aka disorders of arousal), 2) parasomnias associated with REM sleep and 3) other parasomnias. Each of these divisions is further subdivided into more specific parasomnia types; subdivisions for the primary parasomnias are shown in Table 1.


Table 1. Primary parasomnias classified by sleep stage

Parasomnias associated with NREM sleep

Parasomnias associated with REM sleep

Other parasomnias

Confusional arousals

Nightmare disorder

Sleep enuresis


Recurrent isolated sleep paralysis

Sleep-related bruxism

Sleep terrors

REM sleep behavior disorder

Rhythmic movement disorder






Nocturnal groaning


What are the social and economic costs of parasomnias?

Sleep is central to good health and daily functioning. Yet the full scale of the social and economic costs incurred by sleep disorders is not yet completely clear. For 2004, the direct and indirect cost of sleep disorders as a whole was estimated to be $7.5 billion for the Australian population (20.1 million people). This would translate to about $109 billion for the United States2 and $12.3 billion for Canada. But little is known about the economic impact of specific parasomnias. At least two parasomnias, sleepwalking and RBD, warrant more immediate attention because of the injuries and severe sleep disruption they often inflict on patients and their families.

Adult sleepwalking can lead to the destruction of property such as the breaking of walls, doors, windows and plumbing. Behaviors reported for either somnambulism or sleep terrors include running into walls and furniture, jumping out of windows, driving a car, wandering around streets, climbing ladders, sexual activity and manipulating weapons—even loaded shotguns. The fact that somnambulistic episodes can consist of complex and organized behaviors such as suspected suicide, attempted homicide and homicide, raises important medico-forensic questions.3-12 The number of legal cases of sleep-related violence is on the rise13.

RBD can frequently lead to serious injuries 14,15 and are a main reason for clinical consultation. RBD episodes may also cause severe sleep disruption for the bed partner and major marital discord, mood changes, even suicide attempts.16 Beyond these consequences, RBD may be a prodrome for neurodegenerative diseases, especially Parkinson and Lewy body diseases.  In fact, 45% of patients with RBD develop either Parkinson disease, Lewy body disease or multisystemic atrophy after a follow-up of only 5 years.17 A longer follow-up (11 years) reveals that 65% of RBD patients develop a neurodegenerative disorder leading mainly to dementia.18

What are REM sleep parasomnias?

Nightmare disorder

Clinical features

Nightmare disorder is the persistence of disturbing dreams that arise primarily from REM sleep (more rarely from stage 2 sleep) and that usually end up awakening the sleeper.1 Autonomic activation is usually much less than in sleep terrors. There may be dream-enacting behaviors at the end of some nightmares, especially if you are enduring a situation of intense emotional stress and/or sleep disruption, e.g., the postpartum state.19 Awakenings from nightmares are usually abrupt and a detailed disturbing dream is easily recalled. Idiopathic nightmares have no apparent cause and are distinguished from post-traumatic nightmares, which are due to trauma.

Incidence and prevalence

The prevalence of nightmare symptoms is estimated together with their frequency. Nightmares occur occasionally in over 85% of the general population, at least once a month in 8-29% and at least once a week in 2-6%.20-23 A frequency of one nightmare per week likely reflects clinical pathology. Nightmares are less frequent among preschoolers (1.5-3.9% parents report their children have them often or always) than previously thought but may appear as early as 29 months and remain highly stable until age 6 yrs.24 An internet survey of 24,102 respondents25 found the number of nightmares recalled per month peaks between ages 20-29 and then declines steadily. A second internet survey of 3978 respondents found that the distress caused by nightmares increased abruptly at an earlier age for women than for men. A gender difference favoring girls appears in adolescence26,27 and continues throughout the lifespan, as shown in Figure1.25

Figure 1.

Retrospective estimates of monthly nightmare frequency by 5-year age strata in an internet sample of 24,000 respondents.25 *=significant difference between female and male subjects at that stratum, p<.05


Polysomnographic characteristics

Nightmares are often associated with autonomic fluctuations (increased heart and respiratory variability) during REM sleep. But these fluctuations are often less than might be expected from hearing the content of the nightmare.28 In contrast, post-traumatic nightmares are accompanied by heightened reactivity in the form of more frequent awakenings,29 longer time awake after sleep onset,29,30 increased motor and rapid eye movement activity during REM sleep,31-33 and higher REM and NREM sleep respiration rates.34 Both idiopathic and post-traumatic nightmare patients have elevated levels of periodic leg movements (PLMs) in REM and NREM sleep.29

Associated factors

A genetic contribution to nightmares has been found to be 44% for men and 45% for women in the case of childhood nightmares.35 Bad dreams among 29-month-old preschoolers are predicted by mother ratings of difficult temperament as early as 5 months of age and by mother and father ratings of child anxiety as early as 17 months.24 Among adults, nightmares are also associated with psychopathological traits36,37 and personality variables such as:

*       physical and emotional reactivity36,38

*       fantasy proneness39

*       thin boundaries.40-43

Nightmares are more frequent and prevalent in psychiatric populations23,44 and are associated with pathological symptoms such as anxiety, neuroticism, posttraumatic stress disorder, schizophrenia-spectrum symptoms, suicide risk, dissociative phenomena, problematic health behaviors and sleep disorders (see reviews45,46). Nightmares are also more likely during periods of increased life stress.38,47,48

Recurrent isolated sleep paralysis

Clinical features

Recurrent isolated sleep paralysis (aka isolated sleep paralysis or sleep paralysis, SP) is common and generally benign, being characterized by brief episodes of motor or vocal paralysis combined with a waking state of consciousness.1 Frightening dreamlike hallucinations often intrude and can cause considerable distress. SP episodes occur at sleep onset (hypnagogic) and upon awakening (hypnopompic) and is one characteristic of individuals with narcolepsy, which is characterized by cataplexy and excessive daytime sleepiness in addition to SP and hypnagogic hallucinations.1 SP is commonly associated with feelings of fear or terror49 and are often linked to the hallucination of an unseen presence in the room (‘sensed presence’).50,51

Incidence and prevalence

Variations in prevalence estimates (5-40%) depend upon differences in operational definitions, age of subjects and sociocultural factors.52-54 Age of onset is typically 14-17 yrs. Accompanying sensed presence hallucinations occur in 60-69% of cases.50,51,55,56

Polysomnographic characteristics

SP episodes most often arise from sleep-onset REM periods (see Figure 2),57,58 leading to the view that the episodes are bouts of state dissociation during which some REM sleep mechanisms–muscle atonia and vivid dreaming in particular–intrude upon the waking state.59,60

Figure 2.

Somnograms of five healthy subjects reporting sleep paralysis episodes during a multiphasic sleep-wake schedule. Vertical arrows above somnograms indicate awakening points where sleep paralysis episodes were reported. Of 184 awakenings, 8 sleep paralysis episodes were recorded; 2 just prior to impending REM episodes (spontaneous awakenings) and 6 from sleep onset REM episodes (from Takeuchi, et al., 2002).58

Associated factors

Among the factors associated with sleep paralysis episodes are stress,54,58,61 shift work and irregular sleep-wake schedules.53,61 A genetic component has also been reported, e.g., 36% of respondents in a Japanese sample had family members who experienced sleep paralysis.62

Several studies link sleep paralysis to various neurological and psychiatric disorders. It is predicted by bipolar disorder, automatic behavior and use of anxiolytic medications.52 It is also comorbid with PTSD,63,64 depression symptoms,65,66 anxiety disorder with agoraphobia,67 panic disorder,64,68,69 generalized anxiety disorder and social anxiety.70 This wide comorbidity has recently been attributed to mediation by an affect distress personality style (‘sleep paralysis distress’) in a manner analogous to that proposed for nightmare disorder (‘nightmare distress’).50

Associations of SP with psychiatric conditions vary among ethnic groups. Atypically high rates were found in African Americans with panic disorders,69 Moroccan patients,71 Magrebins71 and Cambodians.63 Some of these differences may stem from cultural interpretations of sleep paralysis hallucinations, sensed presence in particular, as a form of spiritual entity, e.g., “ghost oppression” in China,61 “Old Hag” in Newfoundland,72 “the ghost that pushes you down” in Cambodia,63 among many others.

REM sleep behavior disorder

Clinical features

REM sleep behavior disorder (RBD), first described as a clinical entity in 1986,73 is characterized by the loss of skeletal muscle atonia normally present during REM sleep and the occurrence of complex dream-enacting motor behaviors. Diagnostic criteria include a) complaint of violent or injurious behaviors during sleep, b) limb or body movements associated with dream mentation and c) one of the following:

*       harmful or potentially harmful sleep behaviors

*       dream appears to be acted out

*       sleep behaviors disrupt sleep continuity.

In addition, the dream process and its content appear altered. Most patients (87%) report that their dreams become more vivid, intense, action-filled, and violent with the onset of RBD.74 Dream themes associated with behaviors are largely stereotyped in structure and emotional content.73,75 Among published reports of dreams for which investigators identified specific behaviors, the most frequent pattern is of vigorous defense against attacks by people (58.8%) and animals (23.5%) (see review76). Analyses of recently remembered dreams reveal a high percentage of aggressive contents but, paradoxically, normal levels of aggressiveness during the daytime.77

Sleep behaviors can produce injuries to the patient or the bedpartner; these might include ecchymoses, lacerations, fractures and subdural hematomas. Injuries are a main reason for consultation, being reported by 79%-96% of consulting cases.14,15

Incidence and prevalence

The prevalence of RBD is still largely unknown. A telephone survey of violent and injurious sleep behaviors in the British general population (N=4972; 15-100 yrs of age) produced a prevalence of about 0.5 %.78 Another study of 1034 Hong Kong area residents (70+ yrs) found a prevalence of 0.4%.79 It is predominant in males (87%), primarily men over age 50.74 Milder forms of RBD with less aggressive behaviors that do not lead to clinical consultation have been postulated for women.74 Also, dream-enacting behaviors among healthy young students and pregnant and postpartum women have recently been identified by our group.19,80

Polysomnographic characteristics

      Laboratory recordings reveal intermittent or complete loss of REM sleep muscle atonia and excessive phasic EMG activity during REM sleep.75 The PSG diagnostic criteria are presence of:

a)     excessive augmentation of chin EMG tone

b)     excessive chin or limb phasic EMG twitching

c)     one of the following features during REM sleep:

*       excessive limb or body jerking,

*       complex, vigorous or violent behaviours

*       absence of epileptic activity.

Compared with age-matched controls, RBD patients have more SWS81 and distinct changes in the EEG spectrum (e.g., more NREM delta,81 less REM occipital beta,82 more theta in several areas).

Associated factors

RBD is strongly associated with neurodegenerative diseases, especially the synucleinopathy type83 which include:

*       Parkinson’s disease,84,85

*       dementia with Lewy bodies,86-88

*       multiple system atrophy.89-91

RBD is also comorbid with two tauopathies: Alzheimer’s disease92 and progressive supranuclear palsy.93

Even patients with idiopathic RBD show some signs of neurodegeneration. FDG-PET brain imaging of cognitively normal patients with dream-enacting behaviors revealed lower metabolic activity in several brain regions known to be affected in dementia with Lewy bodies.94

Multiple dysfunctions for RBD patients have been described, including:

*       olfactory deficits95

*       color identification deficits95

*       decreased motor speed95

*       EEG slowing,82

*       mild dysautonomia96,97

*       subtle neuropsychological dysfunctions.82,98,99

RBD has also been associated with narcolepsy and other neurological disorders,75 such as:

*       olivopontocerebellar degeneration

*       ischemic cerebrovascular disease

*       multiple sclerosis

*       Guillain-Barré syndrome

*       Shy-Drager syndrome

*       Arnold-Chiari syndrome.

What are NREM sleep parasomnias?

Confusional arousals

Clinical features

Confusional arousals (aka sleep drunkenness) are transitory states of confusional behavior or thought occurring during or after awakenings from NREM sleep, usually from NREM sleep early in the night. The individual is confused, disoriented, behaviorally slow, and may display automatic or inappropriate behaviors. Vivid dreaming is usually not present. Sleep-related abnormal sexual behaviors, such as masturbation, sexual molestation, initiation of sexual intercourse and loud sexual vocalizations during sleep are part of the spectrum of confusional arousals.1

Incidence and prevalence

The incidence is unknown but episodes are frequent in early childhood and diminish after age 5.100 Young children with persisting confusional arousals often become sleepwalkers in adolescence. Prevalence in adults is 3-4 %101. There is no known gender difference.

Polysomnographic characteristics

The arousals usually occur during the first two NREM episodes, but can also occur in later NREM sleep. PSG recordings have shown awakenings from NREM sleep.

Associated factors

Childhood confusional arousals are usually benign; in adults they are often associated with mental disorders or obstructive sleep apnea. They occur more often in night-shift or rotating-shift workers.101 Many conditions can set the stage for confusional arousals:

*       family history

*       sleep deprivation

*       obstructive sleep apnea

*       drug/alcohol use.


Sleepwalking (somnambulism)

Clinical features

Sleepwalking is characterized by behaviors usually initiated during arousals from NREM sleep; it may begin with simple movements, such as sitting up in bed, and culminate in walking, running out of the room,1 or, more rarely, more complex activities, e.g., cooking or eating,102 driving,11 even homicide.3,103-106 Episodes are accompanied variously by amnesia, confusion, perceived threat, dreaming or even pseudo-hallucination. Usually considered benign in children, sleepwalking in adults may lead to injuries.

Incidence and prevalence

Peak incidence (approximately 17%) is around age 12 years.107 For adults, a suggested prevalence of 2-2.5%21,52 is probably an underestimate. Many studies report no gender difference in older children, adolescents or adults,107,108 but studies of young children 2.5-6 and 4-9 years old found it to be more common in boys than in girls.109,110

Polysomnographic characteristics

Sleep architecture does not differ between adult somnambulistic patients and control subjects,111-116 except that somnambulists have more arousals out of NREM sleep.111,113 Episodes of somnambulism are rare in the sleep laboratory, but they may be triggered experimentally by extended sleep deprivation (e.g., 38 hours).117,118

Associated factors

There is a strong genetic component119 with a link to the HLA-DQB1 gene.120 Anxiety may increase occurrences.100,121,122

Sleep terrors

Clinical features

Sleep terrors (aka night terrors or pavor nocturnus) are “arousals from SWS accompanied by a cry or piercing scream and autonomic nervous system and behavioral manifestations of intense fear”.1 Typically, within 90 minutes of falling asleep, the individual screams and sits up with a panic-stricken expression and intense autonomic activity (sweating, racing heart, rapid breathing). Less often there are complex behaviors such as leaving the bed, fleeing the room or thrashing around. Injuries may result in such cases.123 Inconsolability is a key feature; attempts to console or awaken a somnambulist in mid-episode may well prolong or intensify it—even causing aggressive actions toward the intervener. As is the case for somnambulism and confusional arousals, the individual usually does not wake up fully from a sleep terror and will forget the event the following day. Sleep terrors do not differ markedly from somnambulism except that the behaviors displayed are usually more rapid and abrupt than during somnambulism.

Incidence and prevalence

Reported incidence estimates are variable.108,124-126 Some parents may fail to differentiate nightmares and sleep terrors but when a clear definition is supplied, a high prevalence (40%) is seen in preschoolers.110 Sleep terrors tend to resolve in adolescence and do not display a gender difference.108,110 In adults, there is a high degree of overlap among confusional arousals, somnambulism and sleep terrors.

Polysomnographic characteristics

Sleep recordings often show sudden awakenings from NREM sleep, especially in the second half of either of the first two NREM sleep episodes. The amount of time spent in stages 3 and 4 NREM sleep prior to an episode is positively correlated with severity of the subsequent episode.123 Rarely, they may occur in NREM stage 2.

Associated factors

Childhood sleep terrors are usually not associated with a neurological condition, whereas onset in adulthood may be. As is the case for somnambulism and confusional arousals, genetic factors play a major role.  Monozygotic twins are more concordant than dizygotic twins for sleep terrors127 and they are twice as frequent in children for whom one or both parents have a sleepwalking history than for those with non-affected parents.128

What other parasomnias are there?

Sleep enuresis

Clinical features

Sleep enuresis is characterized by recurrent involuntary voiding during sleep at least twice a week among individuals who are at least five years of age.1 It is considered primary if the child has never been constantly dry during sleep and secondary when the child (or adult) had been previously dry for at least six consecutive months and started wetting at least twice a week for at least 3 months.

Incidence and prevalence

Three population-based studies110,129,130 found that between 20 and 33% of children were bedwetting at the age of 5 years. A male predominance in prevalence is well-established.108,110,129,130 Adult enuresis is rare, occurring in about 3% of elderly women (65+ yrs) and 1% of elderly men living at home.131

Polysomnographic characteristics

Although parents commonly consider sleep enuresis to be caused by sleeping too deeply, consistent changes in sleep depth and sleep architecture have not been demonstrated.132 However, a study using polysomnographic recording has shown that enuretic boys are more difficult to arouse from sleep than are age-matched controls.133 For most children, micturition occurs in the first half of the night and is not associated with a specific sleep stage.132 Tachycardia and short EEG arousals are often seen prior to enuretic events.132 

Associated factors

An association between enuresis and delayed achievement of early childhood developmental milestones such as motor skills (for boys) and language (for girls) has been demonstrated.134 This indicates that bed-wetting may reflect delayed development of the central nervous system.  Enuresis is not linked with anxiety in preschoolers110 but is in older children.135-137  However, anxiety is more likely a consequence than a cause of enuresis. Hereditary factors have been recognized; it is inherited via an autosomal dominant mode of transmission.138 Prevalence is 77% when both parents were enuretic as children and 44% when one parent was enuretic.139

Sleep-related bruxism

Clinical features

Sleep related bruxism is the grinding or clenching of one’s teeth during sleep, usually in association with sleep arousals.1 This activity results in tooth wear, headaches, jaw dysfunction and pain. Orofacial morphology is not likely a causal factor since it has been shown not to differentiate sleep bruxers from controls.140

Incidence and prevalence

Sleep bruxism is very common in early childhood. A recent longitudinal, population-based study found that the prevalence increases from 2.5 yrs to reach 33% at 6 yrs of age.110 Another longitudinal study reported a progressive decrease toward adolescence attaining 9% at age 13.108 An age-related decline in prevalence has also been described throughout adulthood in a population-based study.141  Overall prevalence in adults has been estimated to be around 8%.142 No gender difference has been found for either children108 or adults.141 The presence of sleep bruxism in childhood and adulthood are highly correlated.143

Polysomnographic characteristics

Although abnormal tooth wear is highly indicative of sleep bruxism, a definite diagnosis rests on the presence of rhythmic masticatory muscle activity and grinding sounds during all-night polysomnographic recording. Bruxism episodes most frequently occur in stages 1 and 2 but can occur in all stages.144,145 Bruxers have normal sleep architecture and high sleep efficiency, i.e., greater than 90%.144 However, a clear sequence of cortical to cardiac activation preceding jaw motor activity in bruxism patients146 suggests that sleep bruxism is secondary to micro-arousals. In fact, both micro arousals and rhythmic masticatory muscle activity/sleep bruxism episodes were to shown to increase prior to each REM sleep period (see Figure 4).147

Associated factors

Anxiety has been reported as an associated factor in children,108 adolescents and adults.148,149  Smoking also exacerbates bruxism.150 As is the case for many parasomnias, there is a strong genetic influence.143

Sleep-related rhythmic movement disorder

Clinical features

Sleep-related rhythmic movement disorder is characterized by the repetitive, stereotyped, and rhythmic activity of large muscle groups that occurs predominantly during drowsiness (sleep onset) or sleep.1 It can involve any body part although the most frequent rhythmic movements are body rocking, head rolling and head banging. Body rocking may be difficult to distinguish from head banging because the latter movement sometimes includes banging of the head into a solid object. It is largely a parasomnia of infancy and early childhood. The frequency of movements ranges between 0.5 and 2.0 Hz but are more typically around 1 Hz.151  Time spent in rhythmic motion can vary from a few seconds to more than an hour151 but in most cases will occur nightly or almost every night.152 The majority of episodes (around 80%), at least for head banging, occur at sleep onset.152 When appearing at sleep onset, rhythmic movements are considered to be self-soothing or tension-releasing behaviors linked with pleasurable sensations that have hypnotic properties. However, more violent movements, usually in cases of mental retardation, can cause eye or head injuries.153-155

Incidence and prevalence

In infancy, this parasomnia is quite common but decreases rapidly in prevalence with increasing age. Incidences of  66% at 9 mo, 26% at 2 yrs and 6% at 5 yrs had been reported using a sample of children156 but a recent epidemiological study reported lower incidences of about 6% at 2.5 yrs, 3% at 4 and 5 yrs and 2% at 6 yrs.110 Body rocking was found present in 3% of children aged 11 to 13 yrs.108 In rare cases, rhythmic movement disorder persists into adulthood. No gender differences have been demonstrated.

Polysomnographic characteristics

Different case reports indicate that rhythmic movement disorder can arise from REM sleep, NREM sleep or sleep onset with persisting activity in light sleep. Longer movements are usually observed at sleep onset and during stage 1 sleep whereas shorter movements are seen in stages 2, 3, 4 and REM sleep.151 Sleep-related rhythmic movements are not preceded by EEG changes as are nocturnal seizures151 and do not provoke arousals or interrupt SWS even in older children.152,157

Associated factors

There are no reports of rhythmic movement disorder in association with other parasomnias or sleep problems except for restless legs syndrome, which is associated with body rocking.158 Cases of adult rhythmic movement disorder are not usually associated with severe psychiatric disorders as previously believed. However, some studies have reported daytime complaints such as attentional difficulties, sleepiness, morning headaches, fatigue and poor concentration, and even more serious problems such as anxiety, depression, hyperactivity and irritability.151,159,160 Whether the daytime symptoms result from poor sleep caused by the rhythmic movements remains to be determined.


Clinical features

Somniloquy, also known as sleep talking, is defined as talking during sleep “with varying degrees of comprehensibility”.1 Somniloquy is such a prevalent phenomenon that it is considered to be a normal sleep behavior, especially in childhood.

Incidence and prevalence

Although considered the most frequent parasomnia, somniloquy is usually without consequences and thus rarely a reason for consultation. Its prevalence among preschoolers (84%110) is much higher than among older children and adolescents. A prevalence of 30% was found for children aged 11 to 13 yrs using mainly retrospective reports108 while in adults, an estimate of 24% was found using a telephone sampling method.78 There is no apparent gender difference.

Polysomnographic characteristics

Somniloquy can arise from all sleep stages.161 Since there are few systematic polysomnographic studies, no clear profiles have been identified. However, EMG-induced artifact is common and may begin several seconds prior to, and continue for several seconds after, verbalizations.162 Temporary suspension of eye movements and the occurrence of sustained alpha EEG trains during REM sleep somniloquy episodes have also been noted162 as has suppression of theta and alpha activity prior to the utterances.163 Episodes frequently occur in parallel with sleep mentation, but concordance between verbal utterances and ongoing dreamed speech may vary from isomorphic to completely absent.164 As shown in Figure 3, concordances of any kind are more common in REM (82.6%) than in stage 2 (58.2%) or stage 3-4 (34.4.1%) sleep.162

Figure 3.

Sleep-speech / mentation-report concordances in relation to sleep stage (N=122 samples). All 3 types of concordance are more frequent for reports from REM sleep (82.6%) than for reports from Stage 2 (58.2%) or Stage 3-4 (34.4%) sleep (N=23, 67, 32 reports respectively; awakenings with no recall were not included). 1st-order concordances: same words were both spoken and dreamed; 2nd-order concordances: conceptually related words were spoken and dreamed; 3rd-order concordances: dreamed words referred only nonspecifically to spoken words (adapted from Arkin, 1981, p. 120, Table 7.6).162

Associated factors

Since somniloquy is so prevalent, it is virtually impossible to isolate predisposing factors. Nonetheless, there is a clear genetic influence.165 Somniloquy is also the parasomnia that most often co-occurs with other parasomnias. It often accompanies the behavioral manifestations of either REM sleep behavior disorder or somnambulism. Stereotyped vocalizations can also be heard during nocturnal seizures. In most cases, however, somniloquy is idiopathic.

Sleep-related groaning

Clinical features

Also known as catathrenia, sleep-related groaning is defined as “a chronic, usually nightly, disorder characterized by expiratory groaning during sleep, particularly during the second half of the night”.1 Groaning or moaning sounds typically begin two to six hours after sleep onset. The sounds produced are usually loud but the pitch and timbre vary among individuals: groaning, loud humming, roaring, and high-pitched sounds have all been observed. By contrast, within individuals the type of sound is usually fairly constant. Catathrenia is not associated with abnormal motor activity and is qualitatively different from somniloquy. Degree of concordance with sleep mentation is unknown. The affected individual is usually unaware of the problem and, apart from occasional complaints of daytime sleepiness, typically has no other sleep complaints. However, production of the sounds may disturb the bed partner. The identification of this disorder is relatively new, with  approximately 45 cases in total reported in the literature.166-176

Incidence and prevalence

Nocturnal groaning represents less than 1% of the population consulting at a sleep disorder center.170 However, since this parasomnia is without major consequences, there is probably a large number of affected individuals that does not seek medical help. It appears to be three times more prevalent in men than in women although too few cases have been reported so far to be able to determine the gender ratio accurately. Onset is habitually during adolescence or early adulthood and the parasomnia persists for several years.170 The precise time course of the condition is unknown due to lack of follow-up on this recently identified condition.

Polysomnographic characteristics

Catathrenia occurs during either REM or NREM sleep but episodes arise predominantly from REM sleep; only one patient presented groaning exclusively in NREM sleep.170 PSG tracings reveal bradypneic events, often occurring in clusters, with deep inspirations followed by long expirations and monotonous vocalization. There is a high night-to-night consistency of the groaning episodes.171 Although catathrenia is associated with bradypneic events, only one of the reported cases168 had significant obstructive apneas or hypopneas and an oxygen saturation remaining above 90% across the night. Body position does not seem to have any influence.170 Whereas the loud sounds of snoring or obstructive sleep apneas occur during the inspiratory phase, the vocalizations of catathrenia occur during expiration. Unlike sleep apnea, sleep architecture for nocturnal groaners is usually preserved. However, a few patients will show either reduced total sleep time combined with reduced sleep efficiency, or a reduction of either slow-wave or REM sleep.170

Associated factors

Neurological and physical (including otorhinolaryngologic) examination, routine laboratory testing and medical history show no specific anomaly.170-172 Apart from the fact that a small proportion of patients (7%) present concomitant bruxism, there are no associated conditions or obvious predisposing factors.170 As for many parasomnias, catathrenia seems to be, at least in part, genetically determined. In about 15% of cases, there is at least one family relative also affected, sometimes in a way consistent with an autosomal dominant pattern of inheritance.170


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