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doi:10.1378/chest.06-1602
(Chest. 2007; 131:1260-1266)
© 2007 American College of Chest Physicians
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Right arrow Contemporary Reviews in Sleep Medicine

Clinical Identification of the Simple Sleep-Related Movement Disorders*

Arthur S. Walters, MD

* From the Center for Sleep Disorders Treatment, Research & Education, New Jersey Neuroscience Institute, JFK Medical Center, Seton Hall University School of Graduate Medical Education, Edison, NJ.

Correspondence to: Arthur Walters, MD, JFK Medical Center, New Jersey Neuroscience Institute, 65 James St, Edison, NJ 08818; e-mail ArtUMDNJ{at}aol.com

Abstract

Simple sleep-related movement disorders must be distinguished from daytime movement disorders that persist during sleep, sleep-related epilepsy, and parasomnias, which are generally characterized by activity that appears to be simultaneously complex, goal-directed, and purposeful but is outside the conscious awareness of the patient and, therefore, inappropriate. Once it is determined that the patient has a simple sleep-related movement disorder, the part of the body affected by the movement and the age of the patient give clues as to which sleep-related movement disorder is present. In some cases, all-night polysomnography with accompanying video may be necessary to make the diagnosis. Hypnic jerks (ie, sleep starts), bruxism, rhythmic movement disorder (ie, head banging/body rocking), and nocturnal leg cramps are discussed in addition to less well-appreciated disorders such as benign sleep myoclonus of infancy, excessive fragmentary myoclonus, and hypnagogic foot tremor/alternating leg muscle activation.

Key Words: alternating leg muscle activation • benign sleep myoclonus of infancy • bruxism • excessive fragmentary myoclonus • hypnagogic foot tremor • movement disorders • nocturnal leg cramps • rhythmic movement disorder • sleep • sleep-related movement disorders • sleep starts

This review will focus on simple, sleep-related movement disorders. Restless legs syndrome (RLS) and periodic limb movements in sleep (PLMS) are representative of such disorders but will, however, not be covered in detail because they are the subject of another contribution in this series of articles. Parasomnias will also not be covered in detail. As opposed to simple, sleep-related movement disorders, parasomnias are often characterized by complex behaviors during sleep that appear purposeful and goal-directed, but are outside the conscious awareness of the individual and are therefore inappropriate. Rapid eye movement (REM) sleep behavior disorder and disorders of partial arousal (ie, sleep walking, sleep terrors, and confusional arousals) are representative of parasomnias of this type.

The main goal of this review is to teach the reader how to think about all the sleep-related movement disorders in such a way as to come to a proper more narrowly focused differential diagnosis and, ultimately, the proper diagnosis for the simple sleep-related movement disorders. In this context, RLS, PLMS, and parasomnias will be mentioned briefly and will be briefly described when they are in the differential diagnosis of the simple sleep-related movement disorders.

In addition to attempting to make a diagnosis or differential diagnosis based on clinical criteria, it should be emphasized that overnight polysomnography with accompanying video may be necessary to document the nature of the sleep-related movement disorders and to properly differentiate them from other simple sleep-related movement disorders, as well as from sleep-related epilepsy and parasomnias. Figure 1 indicates an approach to the diagnosis of all of the sleep-related movement disorders including the simple sleep-related movement disorders and forms the basis for the subsequent discussion of the simple sleep-related movement disorders.


Figure 1
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  		Figure 1.. Flow chart for the approach to the differential diagnosis of sleep-related movement disorders.

 
Approach to the Sleep-Related Movement Disorders

The most important thing in diagnosing a sleep-related movement disorder is to have the right approach. The first question to ask is whether the movement disorder occurs only during sleep or whether it also occurs during wakefulness. If the movement disorder also occurs during the day, the diagnosis may include but not be limited to daytime movement disorders that persist to varying degrees during sleep. These include such things as Parkinson disease, Huntington chorea, Tourette syndrome, essential tremor, dystonias, ataxia, myoclonus, neuroleptic-induced akathisia, and hemiballismus.1 In general, all of the daytime movement disorders persist during sleep but to a much lesser degree than during wakefulness. Although we will not focus on the daytime movement disorders here, Parkinson disease has been the best studied in regard to its relationship to sleep. Parkinson disease may disrupt sleep in the following several ways2: the rigidity and tremor may disrupt sleep; the dopaminergic drugs used to treat Parkinson disease may cause daytime drowsiness with subsequent napping during the day followed by insomnia at night; the dopaminergic drugs used to treat Parkinson disease may cause nighttime hallucinations and paranoia with subsequent insomnia; urinary incontinence associated with Parkinson disease may cause insomnia; depression, which is very high in patients with Parkinson disease, may cause insomnia with early morning awakenings; and there may be a higher prevalence of other specific sleep disorders with Parkinson disease, such as REM sleep behavior disorder, RLS, and PLMS or sleep apnea.

If the movement disorder occurs only at night, the next question to ask is whether the sleep-related movement disorder appears to be simple or complex. If the movement is complex, you may be dealing with a parasomnia rather than a simple movement disorder. Parasomnias are generally characterized by inappropriate activity during sleep that appears to be simultaneously complex, goal-directed, and purposeful but outside the conscious awareness of the patient, and therefore not truly goal-directed or purposeful at all. Sleep walking, sleep terrors, confusional arousals, and REM sleep behavior disorder are examples of this type of activity.345 Sleep walking, sleep terrors, and confusional arousals are considered to be disorders of partial arousal, and arise most commonly out of stage 3 and 4 sleep. Patients are difficult to arouse and generally do not have dream recall. REM sleep behavior disorder arises out of REM sleep. Patients are more easily aroused and report dream content that corresponds to behavior that the patient exhibits during sleep. For example, the patient may report that he or she was dreaming of swinging a baseball bat, and the spouse may report that the patient was hitting him or her during sleep with swinging motions.345

Another important question to ask is whether you are dealing with epilepsy that is mimicking a movement disorder rather than with a movement disorder. Epilepsy can occur exclusively during the day, exclusively at night, or during both day and night. It can be stereotypic and simple or it can appear to be complex, goal-directed, and purposeful but outside the conscious awareness of the patient, and therefore not truly goal-directed or purposeful at all. Epilepsy can therefore mimic a daytime movement disorder or a parasomnia (eg, with episodes of nocturnal wandering and confusion mimicking sleep walking or REM sleep behavior disorder). Such sleep-related seizures usually arise from the frontal and sometimes the temporal lobes. Epilepsy can also mimic a simple monophasic sleep-related movement disorder. Nocturnal paroxysmal dystonia is such an example. This was originally thought to be a simple sleep-related movement disorder; only later were these brief attacks of dystonia arising out of non-REM sleep discovered to be epileptic in nature. Nocturnal paroxysmal dystonia is now considered to be a form of frontal lobe epilepsy.

Therefore, a good clinical history and a fully attended overnight polysomnogram with full seizure montage and video may be necessary to make this distinction. The stereotypic nature of some of the sleep-related simple movements or complex behaviors in epilepsy help to distinguish it from some of these other disorders.6

Once the physician suspects that a patient is presenting with a simple sleep-related movement disorder, there are some hints that will help to further distinguish one type of movement disorder from another. These will be covered in the following section.

Simple Sleep-Related Movement Disorders

Simple Sleep-Related Movement Disorders of the Jaw and Face
Bruxism: If the movement occurs only in the face and jaw, the diagnosis is probably sleep-related bruxism. Bruxism is the medical term for tooth grinding. A less common consideration is sleep-related faciomandibular myoclonus, which consists of rapid jaw jerks or twitches, compared to the more sustained jaw closure seen in bruxism. According to the latest version of the International Classification of Sleep Disorders, 7 bruxism is characterized as follows. The patient reports or is aware of tooth-grinding sounds or tooth clenching during sleep, and one or more of the following conditions is present: abnormal wear of the teeth; jaw muscle discomfort, fatigue, or pain and jaw lock on awakening; and masseter muscle hypertrophy on voluntary forceful clenching. Also to be diagnosed as having bruxism, the jaw muscle activity must not be better explained by another current sleep disorder, medical or neurologic disorder, medication use, or substance use disorder.7

The prevalence of bruxism decreases across the lifespan but is still very common in the elderly at 3%. The disturbing noise from bruxism can interrupt the sleep of the bed partner. Dental damage and temperomandibular joint syndrome are possible consequences of sleep-related bruxism. The etiology is unknown, but anxiety may be an exacerbating factor.8 The role of dental malocclusion in the pathogenesis of sleep-related bruxism is controversial. Therapy with benzodiazepines and a mouth guard have been successful treatments for sleep-related bruxism.89101112

Simple Sleep-Related Movement Disorders Primarily Involving the Legs
If the legs are primarily or exclusively involved in a simple sleep-related movement disorder, the primary possible diagnoses to consider are RLS and PLMS,1314 nocturnal leg cramps or hypnagogic foot tremor (HFT), and alternating leg muscle activation (ALMA).

RLS and PLMS: Many cases of RLS or PLMS involve only the legs, but the reader should be aware that arm restlessness is common in patients with RLS, being present in 48.7% of the 230 patients in whom idiopathic RLS is diagnosed.15 However, Michaud et al15 point out that every patient who had arm restlessness also had leg restlessness. The authors suggest that in most mild cases of RLS, symptoms are specifically localized to the lower extremities, and only with increased severity do they also affect the arms and possibly other parts of the body.15 Periodic arm movements (PAMs) have also been commonly documented in wakefulness and sleep in patients with RLS.1617 On the other hand, in one study16 of 22 patients, there were patients who had PLMSs without PAMs, but there were no patients who had PAMs who did not also have PLMSs. The demographics, pathophysiology, and treatment of RLS and PLMS are covered in another article in this series.

Nocturnal Leg Cramps: If the movement disorder occurs primarily in the legs, also consider the possibility of nocturnal leg cramps.18 Patients with RLS may complain of a cramping sensation, but if the patient says their leg went into actual spasm, the diagnosis is nocturnal leg cramp. According to the new International Classification of Sleep Disorders,18 the criteria for leg cramps are as follows: a painful sensation in the leg or foot is associated with sudden muscle hardness or tightness indicating a painful muscle contraction; the painful muscle contractions in the legs or feet occur during the sleep period, although they may arise from either wakefulness or sleep; and the pain is relieved by forceful stretching of the affected muscles, releasing the contraction. To be diagnosed as having sleep-related leg cramps, the sleep-related leg cramps cannot better be explained by another current sleep disorder, medical or neurologic disorder, medication use, or substance use disorder.18

Sleep-related leg cramps can occur at any age but occur frequently in the elderly, reaching a frequency of a 6% nightly in adults over the age of 60 years. Predisposing factors include vigorous exercise during the day, peripheral vascular disease, oral contraceptive use, hypomagnesemia, hypocalcemia, and dehydration. Sleep-related leg cramps occur in up to 40% of pregnant women but generally resolve after delivery. Treatment with quinine or vitamin E can sometimes be effective.192021

HFT and ALMA: If the movement disorder occurs primarily in the legs, also consider the possibility of HFT.22 HFT appears to be a fairly common disorder. In 2001, Wichniak et al22 looked at the prevalence of this disorder in 375 consecutive patients with sleep-disorders and found a prevalence of 7.5%. All subjects who were aware of the movements reported that they were able to be suppressed voluntarily. There were a variety of other sleep disorders associated with HFT, and the patients were chosen from among those who came to the sleep laboratory with other complaints. However, in this same study the authors mention deep in their discussion that they had performed polysomnography on a healthy control group of 20 subjects and that these subjects also had a similar prevalence of HFT of 5%.22 In HFT, rhythmic foot movements occur every second or so for several minutes in one or both feet just prior to sleep onset or during light stages of sleep. It may represent a variant of rhythmic movement disorder (RMD). It is considered to be a benign disorder with no known sequelae, and there is no known treatment.2223 ALMA may represent the same disorder except that a single contraction of one leg alternates with a single contraction of the other leg.24 According to the new International Classification of Sleep Disorders,25 the diagnostic criteria for HFT are as follows: the patient reports foot movements (directly experienced or observed by others) that occur at the transition between wake and sleep or during light sleep; polysomnographic or activity monitoring demonstrating recurrent electromyogram (EMG) potentials or foot movement typically at 1 to 2 Hz (range, 0.5 to 3 Hz) in one or both feet; burst potentials longer than the myoclonic range (ie, > 250 ms and usually < 1 s); and trains lasting ≥ 10 s. In addition, the diagnosis of HFT is made when the disorder is not better explained by another sleep disorder, medical or neurologic disorder, medication use, or substance use disorder.25

The etiology of HFT and ALMA remain unknown, and there are no known treatments. However, 75% of patients in one series25 on ALMA were taking antidepressants. The role of antidepressants in the precipitation of ALMA needs to be further delineated in larger series. In the majority of cases, reported patients did not seek any treatment, and in only one patient with ALMA was the patient aware of sudden nocturnal muscle contractions in his legs and a sensation that the legs were vibrating. It is not clear what percentage of patients with HFT and ALMA will even request or need treatment.22232425

Simple Sleep-Related Movement Disorders That Occur Primarily in Childhood
If the simple sleep-related movement disorder occurs in childhood, the following diagnoses should be considered: benign sleep myoclonus of infancy; and RMD.

Benign Sleep Myoclonus of Infancy: If the movement occurs in the neonatal period and does not persist beyond infancy, consider the possibility of benign sleep myoclonus of infancy. This disorder exists only in sleep, and the minute the child is awakened the movements stop.262728293031 In addition, the movements can be precipitated by rocking during sleep.26 These features distinguish it from sleep-related epilepsy, although when the diagnosis is not certain, an EEG may be ordered.29 According to the latest version of the International Classification of Sleep Disorders,27 the following criteria are necessary for the diagnosis: repetitive myoclonic jerks involving the whole body, trunk, or limbs: the movements occur in early infancy, typically from birth to 6 months of age; the movements occur only during sleep; the movements stop abruptly and consistently when the infant is aroused; and the disorder is not better explained by another sleep disorder, medical or neurologic disorder, or medication use.2728293031 Prevalence and etiology are not known. No treatment is usually needed as the course is benign without sequelae and as a rule the symptoms disappear after a few months of life.2728293031

RMD: If the movement disorder extends into early childhood (eg, up to approximately 5 years of age) consider the possibility of RMD.32 In this disorder, children rhythmically bang their head against the pillow every second or so for several minutes or similarly rock back and forth from side to side while in bed. The movements can occur during wakefulness or sleep. Although sleep-related epilepsy is in the differential diagnosis, the characteristic movements make epilepsy far less likely. Also, dissimilar to epilepsy, patients usually can stop the waking movements on request. On rare occasions, RMD will extend into adulthood or will occur de novo in adulthood under conditions of emotional stress. In most cases, these movements do not result in any sleep-related injury and therefore do not result in a disorder. According to the new International Classification of Sleep Disorders,33 RMDs are characterized as follows: the patient exhibits repetitive, stereotyped, and rhythmic motor behaviors; the movements involve large muscle groups; the movements are predominantly sleep related, occurring near naps or bedtime, or when the individual appears to be drowsy or asleep; the behaviors result in a significant complaint (as manifested by at least one of the following: interference with normal sleep; significant impairment in daytime function; and self-inflicted bodily injury that requires medical treatment or would result in injury if preventable measures were not used). In addition, it is required that the rhythmic movements are not better explained by another current sleep disorder, medical or neurologic disorder, mental disorder, medication use, or substance use disorder.33

Rhythmic movements are common in infancy but diminish to 5% by the age of 5 years. However, RMD (ie, rhythmic movements accompanied by biological consequences such as sleep-related injury) is far less common. The soothing effect of vestibular stimulation has been proposed as a cause of RMD. Stress and a lack of environmental stimulation have also been proposed as factors. The most important thing in regard to treatment is to have the parents place the child in a safe environment where injury can be avoided and to assure them that, in most cases, the child will outgrow the movements. For children in whom injury is a concern and in whom RMD persists into sleep, a unique therapy involves having the child practice headbanging in the daytime but coming just short of the pillow. The new learned habit may then persist in sleep. Hypnosis has also been used in such cases. Therapy with benzodiazepines or tricyclic antidepressants can also be considered as therapeutic options.33343536

Other Simple Sleep-Related Movement Disorders
Other simple sleep-related movement disorders that do not fall into any of the other aforementioned categories (ie, involving primarily jaw and face, and the legs, and occurring primarily in childhood) include excessive fragmentary myoclonus (EFM) and sleep starts (ie, hypnic jerks).

EFM: If the simple sleep-related movements are very small (eg, minor movements of the fingers and toes or twitching of the corners of the mouth) and they persist in all stages of sleep, consider EFM as a possibility.37 The movements sometimes resemble muscle fasciculations with no movement across a joint space. In some cases, the disorder is diagnosed strictly as an incidental finding on polysomnography, and no visible movement is present. Even when movements are present, the patient may be totally unaware of their presence. The EMG findings in this disorder resemble the phasic REM twitches that are a normal finding in REM sleep, except that they exist in all stages of sleep and are not clustered as in normal REM sleep, but are more evenly spaced across individual epochs. No treatment is needed for this disorder. According to the new International Classification of Sleep Disorders,38 EFM is characterized as follows: the patient exhibits small movements of the fingers, toes, or corners of the mouth, or small muscle twitches resembling either physiologic hypnic myoclonus or fasciculations; the movements may be present during wakefulness or sleep; polysomnographic monitoring demonstrates recurrent and persistent very brief (75 to 150 ms) EMG potentials in various muscles occurring asynchronously and asymmetrically in a sustained manner without clustering; more than five potentials per minute are sustained for at least 20 min of non-REM sleep stages 2, 3, or 4; and the disorder is not better explained by another sleep disorder, medical or neurologic disorder, medication use, or substance use disorder.38

EFM is more common in older men. EFM may occur in up to 5 to 10% of patients with excessive daytime somnolence of many etiologies. However, as mentioned before, it is unclear whether there is any definite causal relationship between EFM and excessive daytime somnolence since EFM is usually a coincidental finding on polysomnography in patients who have come into the sleep laboratory for complaints related to other pathologies. There is no known treatment, but the need for treatment is unclear.233839404142

Sleep Starts (Hypnic Jerks): If only one or two whole-body jerks happen occasionally just before sleep onset, consider the diagnosis of sleep starts (also called hypnic jerks).4344 This is common and has been experienced by almost everyone at one time or another. Only on occasion are the hypnic jerks excessive and bothersome to the individual. If the jerks are excessive prior to sleep, the differential diagnosis includes the periodic and aperiodic involuntary movements that are relatively commonly seen in patients with RLS.13 In a minority of patients with RLS, these movements may be more prominent than the leg discomfort and may be very rapid or myoclonic in speed. In some cases, these very rapid movements in RLS patients during wakefulness electrophysiologically show the characteristics of propriospinal myoclonus, which is initiated by nerve fibers of spinal cord origin. Propriospinal myoclonus during wakefulness in the absence of RLS and PLMS must also be considered in the differential of sleep starts (hypnic jerks), but this appears to be a much less common disorder.45 According the new International Classification of Sleep Disorders,46 sleep starts (hypnic jerks) are characterized as follows: the patient complains of sudden brief jerks at sleep onset, mainly affecting the legs or arms; and the jerks are associated with at least one condition from among a subjective feeling of falling, a sensory flash, or a hypnagogic dream. In addition, the disorder must not be better explained by another sleep disorder, medical or neurologic disorder, mental disorder, medication use, or substance use disorder.46

Sleep starts are a normal phenomenon occurring in persons of all sexes and all ages with a prevalence of 70%. They presumably arise from sudden descending volleys that originate in the brainstem reticular formation and are activated by the instability of the system at the transition between wake and sleep. Only occasionally do they become excessive, and, in most cases, reassurance that this is a normal phenomenon is all that is needed. There are no known treatments.23434446

Conclusion

The simple sleep-related movement disorders must be distinguished from sleep-related epilepsy, daytime movement disorders, and the parasomnias, which are generally characterized by inappropriate complex behaviors that appear to be goal-directed but are outside the conscious awareness of the individual. The differential diagnosis of the simple sleep-related movement disorders can be narrowed down by body part or age. In some cases, all-night polysomnography with accompanying video is necessary to make the diagnosis.

Footnotes

Abbreviations: ALMA = alternating leg muscle activation; EFM = excessive fragmentary myoclonus; EMG = electromyogram; HFT = hypnagogic foot tremor; PAM = periodic arm movement; PLMS = periodic limb movements in sleep; REM = rapid eye movement; RLS = restless legs syndrome; RMD = rhythmic movement disorder

The author has reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Received for publication June 28, 2006. Accepted for publication January 5, 2007.

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