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Movement Disorders in Sleep 

Movement Disorders in Sleep
Chapter:
Movement Disorders in Sleep
Source:
Acute and Emergent Events in Sleep Disorders
Author(s):

Pasquale Montagna

and Federica Provini

DOI:
10.1093/med/9780195377835.003.0017

Introduction

In human beings, the passage from wakefulness to sleep is accompanied by a progressive decrease in muscle activity. The excitability of spinal motor neurons remains unchanged during deep sleep (slow wave sleep) with respect to quiet wakefulness. The muscle hypotonia that starts and increases during slow wave sleep is therefore due to the abatement of the excitatory stimuli typical of wakefulness. The complete lack of tone of somatic muscles (atonia) is instead characteristic of REM sleep.1 Postsynaptic inhibition is the principal process that is responsible for the atonia of the somatic musculature during active sleep, and this is accompanied by intermittent phasic excitation during the bursts of rapid eye movements.2 These postsynaptic processes depend on the presence of active sleep-specific inhibitory postsynaptic potentials (IPSPs), which are apparently mediated by glycine. Spinal motor neuron excitability is tonically inhibited and further attenuated during rapid eye movements. However, these eye movement discharges are associated with an increase in excitatory stimuli on spinal motor neurons that elicit twitching in experimental animals.3 The phasic excitation of motoneurons during REM periods is due to excitatory postsynaptic potentials (EPSPs) that, when present, encounter a motoneuron already subjected to enhanced postsynaptic inhibition. These EPSPs are mediated by a non-NMDA neurotransmitter. Thus, from a perspective of motoneurons, active sleep can be characterized as a state abundant in potent patterns of postsynaptic inhibition and, during REM periods, not only by enhanced postsynaptic excitation but also by enhanced postsynaptic inhibition. The site of origin of these inhibitory and excitatory drives is, at present, not clearly defined. The structures from which the inhibitory drives emanate are probably located in the lower brain stem, with a cholinoceptive trigger zone situated in the dorsolateral pontine tegmentum in or in the vicinity of the nucleus pontis oralis.2

Sleep does not therefore always achieve a complete quiescence of motor activity. There are indeed physiological motor activities during sleep (e.g., hypnic jerks, the fragmentary myoclonus during sleep, gross body movements) and sleep may be disrupted by a wide variety of movement disorders occurring during the sleep period. In some instances, these sleep-related movement disorders assume an emergent character and may pose safety problems to the sleeper and/or the bed partner. Also, many of the sleep-related motor disorders may be mistaken for other serious and emergent neurological conditions (e.g., epilepsy).

This chapter provides an overview of the most common emergent sleep-related motor disorders. For each sleep motor disorder we detail the clinical salient characteristics, with emphasis on the acute problems they engender and the distinguishing features.

Sleep Starts

Sleep starts, also known as hypnagogic or hypnic jerks, are benign, normal events occurring at the transition from wakefulness to sleep.411 Sleep starts are very common, occurring in approximately 60% to 70% of people of all ages. They consist of a single, non-stereotyped, quick contraction, mainly affecting the upper and lower extremities, sometimes bilateral but more frequently segmental and asymmetric. Fatigue, stress, and sleep deprivation may trigger the jerks. The jerks may be associated with sensory phenomena, including a subjective sensation of falling or a sensory flash.12 In other cases, sleep starts may occur without a body jerk but with only visual, auditory, or somesthetic sensory phenomena.6 The exploding head syndrome, characterized by the brief sensation that an explosive noise has occurred in the head, which wakens the individual from sleep, also represents a purely sensory sleep start.7,8

It has been suggested that the sleep starts represent a release phenomenon due to a transient reduction of suprasegmental descending inhibitory influences as the patient passes from wakefulness to sleep.9

Sleep starts are usually benign phenomena and no cerebral lesion has been described except in rare cases.10 In some patients, however, the sleep starts may be so excessive and severe (so-called intensified hypnic jerks) as to cause a veritable sleep disorder characterized by sleep fragmentation and insomnia.11,12

The clinical characteristics of the sleep starts (isolated, brief jerks, usually associated with psychosensory experience, mainly present during drowsiness) are usually sufficient to make a diagnosis. If sleep starts are intensified they may be difficult to differentiate from propriospinal myoclonus (PSM) at the wake–sleep transition (see later). Hypnic jerks, however, occur as soon as the patient falls asleep, in contrast to PSM, which occurs at the wake–sleep transition and disappears as soon as the patient goes into sleep stage 2.

Repetitive sleep starts should be recognized and clearly differentiated from epileptic seizures, especially if they appear in epileptic patients.13 In these cases a video-polysomnographic recording is very useful for differential diagnosis.

Since in most cases sleep starts do not represent pathology, reassurance that they are a universal component of physiological sleep is appropriate. Benzodiazepines are the drugs of choice to treat cases associated with severe sleep disturbance and daytime drowsiness.

Benign sleep myoclonus of infancy

Benign sleep myoclonus of infancy (BSMI) is a non-epileptic paroxysmal motor event characterized by repetitive, rhythmic or arrhythmic, symmetric or asymmetric, myoclonic jerks involving the whole body, trunk or limbs. BSMI is a benign phenomenon of early life (typically from birth to 6 months of age) in healthy newborns.1416 BSMI occurs only during sleep, in all sleep stages, especially during NREM sleep. Movements are absent during wake and stop if the child is awakened. BSMI may be triggered by noise17 and especially by rocking the child.18 The jerks occur in clusters, lasting 20 to 30 minutes, but one reported case exhibited prolonged jerks lasting for 12 hours and mimicking status epilepticus.19 Brain CT and MRI, and EEG during the jerks are all normal.

BSMI has a self-limited benign course, resolving spontaneously over weeks to months. It leaves no neurological disability, and therefore no medication is required.

The mechanism is unknown. It has been hypothesized to result from a benign disturbance of the brain stem control of sleep14 or from transient immaturity or imbalance of the serotoninergic system.15

The major differential diagnosis of BSMI is epilepsy, but the absence of waking episodes (BSMI stops abruptly and consistently when the infant is aroused) and the absence of EEG epileptiform discharges during or after the episodes15 are the helpful clinical findings for the differential diagnosis.

Propriospinal myoclonus at the wake–sleep transition

PSM at the wake–sleep transition (sleep onset) is a special type of spinal myoclonus with origin in the spinal cord; it is characterized by muscle jerks of an axial muscle and then extending up and down to the rostral and caudal muscles with a slow conduction velocity (in the range up to 16 m/s) supposedly along the propriospinal pathways.20 The muscles of origin of PSM are especially the thoracic and paraspinal muscles. Myoclonic jerks occur as flexion or extension and may be single or repetitive, with or without agonist–antagonist relationship, and the EMG discharges last 100 to 300 ms. In some jerks, myoclonic activity may be restricted to some axial muscles, usually the originating muscles.21 Back-averaging of the jerks did not disclose any concomitant EEG abnormalities. Neurological examination, standard electromyographic and nerve conduction velocities, somatosensory evoked potentials, transcranial magnetic stimulation, motor evoked potentials, and spinal and cranial MRI evaluation are generally normal. However, symptomatic cases do exist. PSM has been reported in patients with infective myelitis,22 cervical trauma,23 syringomyelia,24 and multiple sclerosis25 and after pharmacological treatments (ciprofloxacin, cannabis, interferon-alpha)2628 but in many cases PSM remains idiopathic.

In some cases PSM shows a striking relationship with the vigilance level, arising during drowsiness, particularly when patients try to fall asleep, and gives rise to a severe and persistent insomnia, since patients complain of sudden involuntary axial jerks occurring every night as they are falling asleep.2931 Polygraphic recording in such cases showed that the spontaneous jerks recurred quasi-periodically every 10 to 20 seconds only during relaxed wakefulness and the pre-hypnic period, when the EEG alpha activity spread to the anterior brain regions, while the PSM completely vanished as soon as spindles and K-complexes appeared (Fig. 17–1). Mental and sensory stimulations (simple arithmetic exercises) during relaxed wakefulness stopped the jerks. In rare cases PSM could reappear during intra-sleep wakefulness and upon awakening in the morning.

Figure 17–1. Propriospinal myoclonus at sleep onset. Myoclonic jerks, as flexion of the trunk and limbs (top video figures), appear when the patient is lying down relaxed. The jerks occur at quasi-periodic intervals, when the EEG is characterized by diffuse alpha activity (bottom polysomnographic recordings). EEG (F3-C3; P3-O1); Delt. = deltoideus; Resp. = respirogram. Analysis of a single jerk (inset on the right) shows that muscular activity originates in the right rectus abdominis muscle (R. Rect. Abd.), spreading later to more caudal and rostral muscles. R. = right; L. = left; R. Masset. = masseter; S.C.M. = sternocleidomastoideus; Pect. = pectoralis; Bic. Br. = biceps brachii; Tric. Br. = triceps brachii; Parasp. = paraspinalis; Rect. Abd. = rectus abdominis; Rect. Fem. = rectus femoris; Bic. Fem. = biceps femoris; Tib. = tibialis anterior; Gastr. = gastrocnemius.

Figure 17–1.
Propriospinal myoclonus at sleep onset. Myoclonic jerks, as flexion of the trunk and limbs (top video figures), appear when the patient is lying down relaxed. The jerks occur at quasi-periodic intervals, when the EEG is characterized by diffuse alpha activity (bottom polysomnographic recordings). EEG (F3-C3; P3-O1); Delt. = deltoideus; Resp. = respirogram. Analysis of a single jerk (inset on the right) shows that muscular activity originates in the right rectus abdominis muscle (R. Rect. Abd.), spreading later to more caudal and rostral muscles. R. = right; L. = left; R. Masset. = masseter; S.C.M. = sternocleidomastoideus; Pect. = pectoralis; Bic. Br. = biceps brachii; Tric. Br. = triceps brachii; Parasp. = paraspinalis; Rect. Abd. = rectus abdominis; Rect. Fem. = rectus femoris; Bic. Fem. = biceps femoris; Tib. = tibialis anterior; Gastr. = gastrocnemius.

Patients with a long history of restless legs syndrome (RLS) and involuntary trunk and limbs jerks of the propriospinal type have also been reported.32 In these cases, video-polysomnography revealed jerks during relaxed wakefulness arising in axial muscles with a caudal and rostral propagation at a slow conduction velocity, characteristic of PSM, coexisting with motor restlessness and sensory discomfort in the limbs. The PSM vanished when spindles and K-complexes appeared on the EEG and, at this time, typical periodic limb movements appeared, limited to the legs.32

PSM at the sleep–wake transition was thought to originate in a spinal generator, set into motion by neurophysiological mechanisms specific to the transitional period between wake and sleep (the so-called pre-dormitum of Critchley).33 PSM at the wake–sleep transition thus emphasizes that the transition from wake to sleep represents a peculiar stage with independent neurophysiological, neuropsychological, neuroradiological, and clinical characteristics.3335 PSM is accompanied by severe insomnia, but it does not otherwise endanger the patient’s health. However, occasional patients have such intense and wide jerks that they suffer bruises or get hurt as they bump against the bed or the wall. In exceptional cases, they may be even propelled out of bed. In a particularly severe and uncommon case of PSM, myoclonic activity in the axial muscles progressed into a “myoclonic status” associated with respiratory failure and loss of consciousness.36 This severe progression required prompt emergency maneuvers and adequate pharmacotherapy.

PSM may be mistaken for epilepsy. The time of occurrence of the jerks (confined to the wake–sleep transition or to intra-sleep arousals), their frequent recurrence, and their suppression by mental and sensory stimuli are the useful hallmarks distinguishing PSM from epileptic phenomena. Video-polygraphic recording is, however, required to confirm the diagnosis.

Benzodiazepines, clonazepam (0.5 to 2 mg/day at bedtime) in particular, can reduce the intensity and frequency of the jerks, making sleep more restful. Opiates may also be effective but carry the risk of dependence.29

Nocturnal Cramps

Cramps are sudden, involuntary, intensely painful muscle contractions lasting up to a few minutes, usually involving the calf muscles. Cramps can occur while at rest or during the night, disrupting sleep. They are associated with sudden muscle hardness or tightness and are relieved by forceful stretching of the affected muscles. The cramps may subside spontaneously, but patients learn to lengthen the cramping muscle by forcibly dorsiflexing the foot or the toes, in order to stop the cramping. Sometimes the nocturnal cramps are so severe and recurrent as to force the patient to jump out of bed and walk.35 Residual discomfort and tenderness may persist for hours afterwards. Nocturnal cramps are a common problem, affecting persons in any age group, but they are especially frequent in the elderly: almost one third of people aged over 60 years experience nocturnal cramps.37

Electrolyte imbalance (hyponatremia, hypomagnesemia, hypocalcemia, and dehydration), drugs (diuretics, nifedipine, beta-agonists, steroids, lithium), medical conditions (uremia, diabetes, liver cirrhosis, hypertension, vascular diseases affecting the legs, heart, and brain, thyroid disease, continuous motor unit activity syndromes like neuromyotonia, myotonia, late-onset lipid storage myopathies, and the myokymia-cramp-fasciculation syndrome), and pregnancy all represent known causes for cramps.38 Muscle cramps are a feature of many myopathic and neuropathic conditions in which they are not usually restricted to the nighttime or necessarily to the legs. Nocturnal leg cramps are particularly frequent in Parkinson’s disease, where they may be relieved by long-acting levodopa formulations.39 Predisposing factors for cramps include vigorous exercise during the day, peripheral vascular disease, and oral contraceptive use.40 Nevertheless, in many cases nocturnal leg cramps occur as an idiopathic condition41 and in some cases they may be a familial condition with an autosomal dominant pattern of inheritance.42

The pathophysiology of the muscle cramps is still uncertain. Polysomno-graphic recordings show increased electromyographic activity in the affected leg and electromyographic studies suggest that cramps result from spontaneous firing of groups of anterior horn cells followed by contraction of several motor units at rates of up to 300 Hz, considerably higher than occurs in voluntary muscle contraction.43 A distal origin in the intramuscular motor nerve terminals has also been proposed.41

A careful examination of the neuromuscular system is essential in patients with troublesome cramps, and investigations such as creatine phosphokinase, aldolase, electromyography, and nerve conduction studies may be indicated in selected patients.

Nocturnal leg cramps should not be confused with RLS, a crawling sensation that is relieved by walking or moving around. Both occur during the night and in the lower extremities and are relieved by movements. Although uncomfortable, RLS typically does not involve cramping, and if patients say that their leg muscles went into actual spasm, the diagnosis is nocturnal leg cramps.

A nonpharmacologic approach (local massaging and passively stretching the affected muscle) is the recommended first-line treatment for idiopathic cases. Treatment with vitamins of the B group and vitamin E may be effective in the management of idiopathic cases.44 Some data support the efficacy of verapamil, gabapentin, carisoprodol, and orphenadrine,45 but the most frequently used treatment is quinine sulphate,46 although its efficacy has not been definitively established in clinical trials, and there has been considerable controversy about its safety. Quinine sulfate has indeed been associated with serious complications involving the hematologic, renal, neurologic, cardiac, and endocrine system, and careful surveillance should be exercised when the drug is prescribed.45 It is no longer available in the United States.

Sleep-Related Rhythmic Movement Disorder

Sleep-related rhythmic movement disorder (RMD) consists of repetitive, stereotyped, and rhythmic movements that occur most frequently at the sleep–wake transition and during stage 1 and 2 NREM sleep.47 RMD can involve any part of the body, with frequency ranging from 0.5 to 2 Hz. Episodes can last up to 15 minutes.12 The four more common types of RMD are head-banging (the head is forcibly moved in a back-and-forward direction), head-rolling (the head is moved laterally while supine [lying on the back, face up]), body-rocking (the whole body is rocked while on the hands and knees), and body-rolling (the whole body is moved laterally while in a supine position). Children are generally unresponsive during the episodes and amnestic for the events on awakening.47RMD is typically seen in infants and children, with a 4:1 male predominance.48 Although occasionally associated with developmental delay, the majority of RMD cases occur in normal children as a benign, self-limiting phenomenon, generally resolving spontaneously by the age of 3 to 4 years.49 In some cases, however, RMD may persist or appear de novo during adulthood and in autistic or mentally retarded individuals47,5052 as well as in adult patients with RLS53,54 (Fig. 17–2) and in the context of REM sleep behavior disorder episodes.55

Figure 17–2. Rhythmic movement disorder. Rhythmic movements of trunk and leg muscles, occurring at about 2 Hz during wakefulness, before sleep onset, in a patient with restless legs syndrome. EEG (C3-A2); R. = right; L. = left; EOG = electro-oculogram; Mylo. = mylohyoideus; Delt. = deltoideus; Parasp. = paraspinalis; Rect. Fem. = rectus femoris; Biceps Fem. = biceps femoris; Resp. = thoraco-abdominal respirogram.

Figure 17–2.
Rhythmic movement disorder. Rhythmic movements of trunk and leg muscles, occurring at about 2 Hz during wakefulness, before sleep onset, in a patient with restless legs syndrome. EEG (C3-A2); R. = right; L. = left; EOG = electro-oculogram; Mylo. = mylohyoideus; Delt. = deltoideus; Parasp. = paraspinalis; Rect. Fem. = rectus femoris; Biceps Fem. = biceps femoris; Resp. = thoraco-abdominal respirogram.

The etiology for RMD is unknown.56 RMD most likely represents a release phenomenon due to the activation of a subcortical central pattern generator as a result of a transient diminution of descending suprasegmental inhibitory inputs.9 RMD in most instances does not represent a real danger for the sleeper. Parents are however often alarmed by the possibility of the child incurring injuries, and, especially when RMD also occurs during the daytime and in autistic or mentally retarded children, it does pose problems of safety. The repetitive and forceful banging of the head or limbs against the bedposts or the wall may indeed cause severe lesions, from the so-called “head-banger tumor” on the forehead (due to the repeated banging) to ocular and scalp and even intracranial hemorrhages.57 In such cases, RMD constitutes an emergency. Besides preventive measures (helmet, restriction), RMD may need emergency medical attention.

RMD is usually easy to diagnose. In the uncommon situations when the clinical presentation is not sufficient to provide diagnostic certainty, video-polysomnographic monitoring can be useful to record the characteristic movements.49

In most cases of RMD pharmacological treatment is unnecessary: the family can be reassured that the condition will remit spontaneously. However, in the severe forms, when vigorous or persistent RMD may result in injury, it can respond to low doses of clonazepam58 and neuroleptics (the latter in autistic or mentally retarded patients).59 For children with developmental disabilities, the use of a protective helmet or padding the sides of the crib or bed may be necessary to prevent injury.

Sleep Bruxism

Sleep bruxism (SB) or teeth-grinding is the repetitive, audible grinding or clenching of the teeth by rhythmic contractions of the masseter and other masticatory muscles during sleep. Three types of SB have been described: tooth grinding with friction sounds, tooth clenching, and tooth tapping.

The movement is involuntary and the patient is completely unaware of the phenomenon. SB comes to medical attention because it disturbs the patient’s bed partner, or because it results in significant temporomandibular joint and muscle pain and/or jaw lock and headache. Sometimes the disorder is first recognized by a dentist, since it can lead to wear of the teeth, particularly evident on the incisal edges of the anterior teeth and on the cups of the posterior teeth. SB can be particularly destructive since movements are associated with lateral grinding and may thus lead to significant tooth damage and hypermobility and to ulcerations of the buccal mucosa.35

Occasional SB is a very common condition, affecting the majority of the population (85% to 90%).60 It occurs most commonly in children, without any gender difference, and then decreases throughout life. Frequent SB is present in about 5% to 8% of adults.60 Smoking, caffeine, and heavy alcohol drinking, anxious personality traits, and the presence of sleep disorders such as sleep apnea or periodic limb movements in sleep (PLMS) can exacerbate SB.61

The mechanisms by which SB is produced are poorly understood, but SB seems clearly different from diurnal bruxism, which is mainly related to stress and anxiety reactivity and is probably harmless.61 In the past various explanations of the pathophysiology of SB were advanced, from a loss of corticobasal ganglia inhibition62 to a possible involvement of the dopaminergic system.63,64 Recent hypotheses suggest that the onset of SB episodes is under the influence of brief and transient activity of the brain stem arousal-reticular ascending system contributing to the increase of activity in autonomic-cardiac and motor modulatory networks.64

In SB patients, no permanent resolution of oromotor activity has yet been demonstrated. If necessary, each subject has to be individually evaluated and treated with dental, pharmacological, or psychobehavioral therapy.60 SB represents a life-long danger to the dental apparatus and a cause of headaches secondary to temporomandibular joint disease.65

The clinical diagnosis of SB is usually straightforward, although the major challenge is to discriminate the oromandibular activity of interest from other non-SB-related oromandibular activities, which are very frequent in normal subjects. Obviously, this requires the witnessing by the patients’ bed partners. Clinical examination confirms the presence of tooth wear or jaw muscle hypertrophy. In doubtful cases, audio-video polygraphic recording of EEG, muscle activity from electromyograms of jaws and legs, and vegetative parameters (heart rate and respirogram) could be helpful. Continuous recording of sounds or careful reports by vigilant technicians on the type of sound heard are the best way to identify SB, since the grinding noise of bruxers is characteristics.60

Polysomnographic recordings demonstrate that bruxism occurs in all stages of sleep, mainly during stage 2 of NREM sleep, and is characterized by forceful, approximately 250-ms-long rhythmic, or tonic prolonged contractions of the masticatory muscles in the absence of associated abnormal EEG activity.64

In the differential diagnosis, rhythmic jaw movements can be also observed during temporal lobe seizures, but in these cases the movements include a more diffuse oro-alimentary behavior and are often preceded by an arising gastric aura and accompanied by other motor automatisms not limited to the face. These particular cases can be detected with polygraphic ictal recordings.66

SB should be distinguished from sleep-related faciomandibular myoclonus (SFMN), which consists of spontaneous forceful myoclonic jerks involving the oromasticatory and cervical muscles, evident only during sleep67,68 (Fig. 17–3).The SFMN jerks, often associated with biting of the tongue and lips, can simulate epileptic seizures during sleep. SFMN usually starts in adult life and may be familial.67 SFMN can mimic SB, but rhythmic tooth grinding, chewing-like muscle contractions, temporomandibular joint pain, abnormal tooth mobility, tooth wear, and other dental problems typical for bruxism are usually absent. SFMN does, however, cause nocturnal awakenings due to painful tongue biting and bleeding, leading to severe lesions and in rare cases even to a resection of tongue tissue.6769 Patients often find a blood-stained pillow upon rising in the morning, and this often causes misdiagnosis of an epileptic seizure. Neurophysiological investigations of SFMN show that the myoclonic jerks persist throughout sleep67 or during REM sleep69 and have no cortical potential on EEG back-averaging. SFMN seems to represent a variety of brain stem reticular myoclonus, not reflexive in origin.67

Figure 17–3. Polysomnographic recordings during an episode of faciomandibular myoclonus involving the masticatory and facial muscles during light sleep. EEG (C3-A2; O2-A1); EOG = electro-oculogram; Mylo. = mylohyoideus; Orb.Eye = orbicularis oculi; Orb.Oris = orbicularis oris; S.C.M. = sternocleidomastoideus; Tib. Ant. = tibialis anterior; microph. = microphone; Thor. Resp. = thoracic respirogram; Abdom. Resp. = abdominal respirogram.

Figure 17–3.
Polysomnographic recordings during an episode of faciomandibular myoclonus involving the masticatory and facial muscles during light sleep. EEG (C3-A2; O2-A1); EOG = electro-oculogram; Mylo. = mylohyoideus; Orb.Eye = orbicularis oculi; Orb.Oris = orbicularis oris; S.C.M. = sternocleidomastoideus; Tib. Ant. = tibialis anterior; microph. = microphone; Thor. Resp. = thoracic respirogram; Abdom. Resp. = abdominal respirogram.

Clonazepam treatment (1 to 1.5 mg at night) may reduce the severity of SFMN.67,69

Sleep paralysis

Recurrent or isolated sleep paralysis (ISP) describes a transient fright-ening inability to move the body at sleep onset or on awaking from sleep.12 Sleep paralysis represents one characteristic element of the narcoleptic tetrad.12 However, ISP occurs occasionally also in normal subjects, especially in association with sleep deprivation, not accompanied by features of narcolepsy such as daytime sleepiness or cataplexy. Each episode lasts from seconds to a few minutes and is usually characterized by intense anxiety. ISP may be associated with hallucinatory and proprioceptive phenomena, both visual and auditory (such as feeling the presence of others nearby, pressure on the chest, or hearing footsteps).9 Consciousness remains intact during the episodes. Episodes may resolve spontaneously or when the patient is touched by a bed partner.

ISP is found in approximately 6% of the general population70 and is more common in adolescents and young adults. ISP has been described in a variety of ethnic populations, and different cultural factors may influence the reporting. In Japan, the condition has been termed “kanashibary,” while terms like “old hag” and “kokma” have been used to describe the condition in Newfoundland and the West Indies, respectively.9 ISP is hypothesized to result from intrusion of elements of REM sleep like muscle atonia into wakefulness. Unless narcolepsy is suspected by history, polysomnography is generally not necessary.

The differential diagnosis of ISP includes partial seizures, especially atonic seizures; the latter, however, occur during wakefulness. Hypokalemic periodic paralysis that may occur at rest and on awakening also mimics ISP, but episodes of hypokalemic periodic paralysis usually last hours and are accompanied by hypokalemia.12

While the episodes are acute in presentation and can be scary for the patient, reassurance and education (including advice about sleep hygiene) are the most useful treatments in ISP. If the frequency of SP is bothersome to patients, low doses of tricyclic antidepressants, clonidine, clonazepam, or SSRIs may be of some benefit, likely because of their REM-suppressing properties.9

Sleep-Related Eating Disorders

Abnormal eating during the main sleep period has been categorized as either night eating syndrome (NES) or sleep-related eating disorder (SRED). NES is an eating disorder due to a delay in the circadian timing of food intake that is abnormally increased in the second half of the day. NES was first described by Stunkard et al71 among patients with treatment-resistant obesity at a specialty center and included evening or night hyperphagia (consumption of at least 25% of the total daily calories after the evening meal), insomnia with awakening followed by nocturnal food ingestion, and morning anorexia with negligible food intake at breakfast. The NES definition was expanded in a study published in 1999, but until now uniform criteria are lacking and most studies do not explain the nosological distinction between NES and SRED.72 NES is often a chronic phenomenon,73 with a prevalence of approximately 1.5% in adult populations.74 There seems to be agreement about a higher prevalence of NES in overweight and obese treatment-seeking patients.

SRED is instead a parasomnia that can be associated with other sleep disorders. In 1991, Schenck et al described a case series of 19 adult patients who had a combination of sleep (mainly somnambulism or PLMS) and eating disorders.75 A follow-up report of 38 patients including those from the same series was published 2 years later.76 An associated primary sleep disorder, particularly sleepwalking and RLS, was identified respectively in 68% and 13% of patients with SRED and is presumed to represent a major predisposing factor for the emergence of the nocturnal eating episodes.76 SRED is characterized by recurrent episodes of eating after an arousal from sleep, typically within 2 to 3 hours of sleep, with ingestion of food often in an out-of-control, compulsive manner, despite absence of hunger. Patients may consume high-calorie foods (carbohydrates and fats) and sometimes bizarre substances. Alcohol consumption during the nocturnal episodes is rare. In some cases, there is an association between compulsive eating during sleep and compulsive smoking: the patients wake up with a desire to smoke and/or eat because of an inner drive.77 Eating lasts a few minutes and may occur up to eight times nightly, although one or two episodes per night are common. Patients were described as displaying reduced or, more rarely, full awareness during the episodes and usually had subsequent amnesia for the nocturnal episodes.76,78 In our case series of 35 patients studied with video-polysomnography, eating episodes occurred, however, with normal consciousness and recall.79 Therefore, while the presence of impaired consciousness has been proposed as a feature distinguishing NES from SRED, the level of awareness during the eating episodes awaits further study.73 The prevalence of SRED is probably underestimated, occurring from 1% to 5% in the general population.80 Most patients are women, and the mean age of onset is during adolescence or early adulthood. The onset of SRED can be sudden, associated with major life stresses or cessation of cigarette smoking or alcohol use, or it can develop gradually, without any identified precipitant. Sporadic cases of drug-induced SRED have been reported with use of tricyclic antidepressants, anticholinergics, lithium, triazolam, olanzapine, and risperidone.73 More recently, cases of SRED has been described during treatment with zolpidem.81

Video-polysomnographic recordings are useful to characterize SRED, showing in most of the cases peculiar subcontinuous orofacial automatisms with chewing and swallowing during sleep,79 and its frequent association with other sleep disorders, in particular periodic limb movements and RLS.79 In a recent case–control study of 200 subjects, we documented that SRED was more prevalent in RLS patients than controls (33% versus 1%, p < 0.001).82

SRED pathogenesis remain unclear, and a hypothalamic dysfunction, involving the orexins as candidate substances, has been hypothesized. Its association with PLMS and RLS, the presence of chewing activity during sleep, the reported efficacy of dopaminergic medications,83,84 and the compulsive food-seeking behavior85 seems to suggest an involvement of the dopaminergic system in the pathogenesis of SRED.

SRED has been associated with injuries and adverse health consequences. Patients frequently report dangerous behaviors during the nocturnal episodes, such as consumption of inedible substances, dangerous food preparation behavior, sleep-related injury, and burns and even setting fires to the kitchen and house.12,73,78 Fear of gaining weight is frequent, and in an attempt to control their overall caloric nocturnal intake, patients sometimes develop daytime anorexia. It is important to recognize SRED because it is a potentially treatable disorder. Abnormal eating can be controlled by treating the comorbid sleep disorders (sleepwalking, PLMS, RLS). Clonazepam, codeine, and carbidopa/levodopa or bromocriptine have been reported as effective treatments in idiopathic SRED. Fluoxetine (in patients with depression and abuse) and D-fenfluramine (a potent serotoninergic agent) are also effective. Although no randomized controlled trials are available, bedtime topiramate or dopaminergic drugs (levodopa, pramipexole, bupropion) are the preferred therapies.73

Nocturnal frontal lobe epilepsy

Among the partial epilepsies, frontal lobe seizures are the most common during sleep. Nocturnal frontal lobe epilepsy (NFLE) is a particular form of partial epilepsy in which seizures are characterized by bizarre, repetitive, and stereotyped motor behavior, or sustained dystonic or dyskinetic postures involving the trunk as well as the limbs. The clinical spectrum of NFLE includes manifestations with variable duration and complexity: paroxysmal arousals (PAs), nocturnal paroxysmal dystonias (NPDs), and nocturnal wandering (ENW).8688 PAs are abrupt arousals from sleep with vocalization and stereotyped motor activity (head movements, frightened expression, dystonic posturing of the limbs) lasting less than 20 seconds and occurring several times throughout the night.89 NPDs are complex motor episodes with violent, sometimes bizarre motor behavior (choreoathetoid, ballistic or repetitive movements of the trunk and limbs and/or asymmetric tonic or dystonic posturing), vocalization, and fearful screaming (Fig. 17–4). ENW involves more complex events, beginning as a PA but then developing into full-blown NPD with vocalization and screaming, and in addition progressing to agitated and repetitive jumping about as in a grotesque dance with stereotyped paroxysmal ambulation.90 The motor behavior during NFLE may be so violent as to become injurious to the patient and/or the bed partner; these patients often suffer recurrent injuries in the course of the disease.91

Figure 17–4. Photographic sequence of 12 images taken at 2-second intervals (upper part) and scalp EEG recordings (lower part) of a nocturnal frontal lobe epilepsy seizure (nocturnal paroxysmal dystonia type). The patient suddenly sits up in bed, rocks his pelvis, opens his legs and arms, grasps the mattress with his right hand, makes repetitive movements up and down in bed, and shouts, raising his hands to the head. The seizure appears during stage 2 NREM sleep. Ictal EEG tracings do not show clear-cut epileptiform discharges but only a diffuse flattening and are soon masqueraded by muscular artifacts. R. = right; L. = left; EOG = electro-oculogram; Mylo. = mylohyoideus; Tib. Ant. = tibialis anterior; Abdom. Resp. = abdominal respirogram.

Figure 17–4.
Photographic sequence of 12 images taken at 2-second intervals (upper part) and scalp EEG recordings (lower part) of a nocturnal frontal lobe epilepsy seizure (nocturnal paroxysmal dystonia type). The patient suddenly sits up in bed, rocks his pelvis, opens his legs and arms, grasps the mattress with his right hand, makes repetitive movements up and down in bed, and shouts, raising his hands to the head. The seizure appears during stage 2 NREM sleep. Ictal EEG tracings do not show clear-cut epileptiform discharges but only a diffuse flattening and are soon masqueraded by muscular artifacts. R. = right; L. = left; EOG = electro-oculogram; Mylo. = mylohyoideus; Tib. Ant. = tibialis anterior; Abdom. Resp. = abdominal respirogram.

In NFLE, there are several attacks per night, every night. Seizures typically occur out of NREM sleep, at any time during the night, with stereotyped motor patterns and an important autonomic activation.87 The seizures often increase in complexity and duration even during a single night: the increasing complexity of the ictal motor behavior reflects a different duration and propagation of the discharge within the frontal lobe.86,92 Clearcut ictal and interictal EEG epileptic abnormalities are absent in over 40% of the cases.87,9395 The persistence of nocturnal seizures and the consequent sleep fragmentation and reduction of sleep efficiency can have a significant impact on the quality of life of the patients because of excessive daytime somnolence.95,96

NFLE affects all age groups, and the age at onset of the attacks is 14 years as a mean; more than 70% of the patients are males.

NFLE is a heterogeneous disease with sporadic, idiopathic, cryptogenic, and symptomatic forms.87,97 In only 13% of the cases are there identifiable causative factors (such as perinatal asphyxia/febrile convulsions), and neurological examination is normal in 92% and brain CT/MRI in 86% of the cases.87

NFLE may be familial. In 1994, Scheffer et al described a genetic form of NFLE called autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE).98 Mutations in the alpha-4, alpha-2, and beta-2 subunits of the neuronal nicotinic acetylcholine receptor (nAChr) were found in individuals with ADNFLE, and recent studies found mutations in other genes, such as the promoter of the corticotropic-releasing hormone gene (CRH).99103

NFLE is often misdiagnosed as a sleep disturbance, the diagnostic confusion arising from the absence of ictal or interictal EEG epileptiform discharges in EEG scalp recordings in many cases.93,104 Therefore, the absence of epileptic surface EEG activity during an episode does not exclude the possibility of seizures, as some patients have ictal discharges that are not apparent on surface EEG.105,106 Moreover, some motor events observed in the arousal parasomnias and in the epileptic seizures may have similar features and resemble motor behaviors, which have been attributed to the expression of the same “central pattern generators.”107 Thus, video-polysomnography and history-taking remain the most important tools to distinguish NFLE from other non-epileptic paroxysmal motor disorders during sleep, particularly the arousal parasomnias.106

Evaluation must begin with a careful clinical interview with the sleeper and family members, with emphasis on a detailed description of the nocturnal episodes. Moreover, it is necessary to ascertain the frequency and duration of the episodes and the timing after sleep onset of the events. Prompting the patient to make audio-video recordings at home with subsequent data analysis may facilitate the diagnosis, and this often adds details that are missed in descriptions given by relatives. Video-polysomnographic monitoring with extended EEG montages (including standard bipolar EEG according to the International 10–20 System, electro-oculogram, ECG, chin and limb muscles electromyogram, and chest and abdominal respirogram) must be considered if the clinical evaluation is inconclusive.108 If the nocturnal episodes are brief, stereotypic, complex, or repetitive, with dystonic and dyskinetic postures, if they are injurious or have significant potential for injury, if they begin at an unusual age, appear stereotypical or repetitive, occur at any time in the night, or are frequent (many times per night on nearly all or all nights) and if the patient complains of excessive daytime sleepiness, a diagnosis of NFLE is more probable.106

NFLE can be controlled with antiepileptic drugs in about 70% of pa-tients.87 Some patients with drug-resistant NFLE are good candidates for surgical treatment:97 the seizure-freedom rates in these cases were significantly higher (up to 75%) than those reported in other types of frontal lobe epilepsy surgical series, likely suggesting a more benign surgical prognosis of NFLE compared to other partial epilepsies. In surgical cases, the resected lesions were mostly characterized by the presence of focal cortical dysplasias of the Taylor type.97

Conclusions

Some of the emergent sleep-related movement disorders discussed here, in particular the simplest ones (sleep starts, benign sleep myoclonus of infancy), do not usually represent pathological phenomena, and it is enough to reassure the patient or family that they occur also in normal people. No drug therapy is necessary, and the main problem they pose is a differential diagnosis with other, especially epileptic phenomena. Other sleep-related movement disorders, however, such as PSM at sleep onset, may become really troublesome, not only because they need to be differentiated from epileptic myoclonus, but also because they cause severe insomnia and, when very intense, may cause bruises and body injuries. RMD is potentially very dangerous, in particular when it occurs associated with mental retardation or in autistic children. In these cases, RMD may be highly resistant to treatment. Bruxism during sleep represents a cause of headache and is also injurious to the teeth and the oral cavity, and the harm associated with its frequent recurrence during the night is compounded by the fact that the patient is usually unaware of it. Therefore, it requires a high degree of clinical suspicion. Finally, SRED and NFLE are likewise potentially injurious disorders. The former, occurring with a reduced level of awareness, may cause bruises, cuts, and even fire accidents, besides being associated with weight gain and other adverse health effects. The latter, because of the frantic and excessive movements it involves, often leads to injuries to the limbs during the seizure; it requires full evaluation for a complex diagnosis, the exclusion of intracerebral lesions, and, when familial, provision of genetic counseling.

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