INTRODUCTION — Sleep-related movements are commonly observed on polysomnography (PSG) and are often benign. However, certain movements warrant further investigation when they negatively impact sleep quality, resulting in daytime symptoms or injury.
While there is no standardization of the reporting process for sleep-related movements, the American Academy of Sleep Medicine (AASM) scoring manual provides guidelines regarding the required and recommended data that should be reported [1]. A clear summary and interpretation are critical so that referring providers can glean the information necessary to make clinical decisions.
Important elements of in-laboratory PSG recordings of simple sleep-related movements are reviewed here. More detailed reviews of the clinical features, evaluation, diagnosis, and management of sleep-related movement disorders are presented separately. (See "Approach to abnormal movements and behaviors during sleep" and "Clinical features and diagnosis of restless legs syndrome and periodic limb movement disorder in adults" and "Management of restless legs syndrome and periodic limb movement disorder in adults".)
PSG in the evaluation of more complex movements, including parasomnias such as sleepwalking and rapid eye movement (REM) sleep behavior disorder, is also reviewed separately. (See "Polysomnography in the evaluation of parasomnias and epilepsy".)
RECORDING SLEEP-RELATED MOVEMENT
Technical points — Polysomnography (PSG) consists of the simultaneous recording of multiple physiologic variables during sleep (figure 1):
●Electrooculogram (EOG) captures eye movement.
●Electroencephalography (EEG) captures brain wave activity.
●Electromyography (surface EMG) captures muscle activity/movement.
●Electrocardiogram (ECG) captures electrical activity from one or two heart leads.
●Respiratory airflow channels (nasal cannula and thermistor) measures the number and depth of respirations and whether there are episodes of shallow breathing (hypopneas) or episodes of breathing cessations (apneas).
●Respiratory effort channels capture the excursions of the chest and abdomen.
●Pulse oximetry continuously monitors oxyhemoglobin saturation in the blood.
●Video monitoring (time synchronized with all other PSG physiologic recordings) uses infrared-sensitive cameras and nonvisible infrared lighting during the study to capture abnormal movements or behaviors.
As with most procedures, data and subsequent interpretation are only as good as the technical strength of the data collection process. As such, accredited sleep laboratories adhere to technical guidelines for recording, scoring, and staging sleep in accordance with the American Academy of Sleep Medicine (AASM) scoring manual; specifications particularly relevant to sleep-related movement are listed in the table (table 1) [1].
PSG scoring and staging relevant to other aspects of sleep are reviewed separately and can be referenced in the AASM scoring manual [1]. (See "Overview of polysomnography in adults" and "Polysomnography in the evaluation of sleep-disordered breathing in adults" and "Polysomnography in the evaluation of parasomnias and epilepsy" and "Overview of polysomnography in infants and children".)
Movement artifacts — Certain PSG artifacts can potentially be confused with physiologic sleep-related movements (waveform 1). Clinicians reading and interpreting sleep studies need to be familiar with these artifacts to avoid false labeling of physiologic movements.
DEFINITIONS OF SPECIFIC MOVEMENTS
Periodic limb movements of sleep — Periodic limb movements of sleep (PLMS) are observed on the leg surface electromyography (EMG) channel(s) of a PSG measured from the anterior tibialis (waveform 2). A minimum of four leg movements occurring within a 5- to 90-second interval is required to be considered a periodic leg movement series. A qualified leg movement is formally defined by the American Academy of Sleep Medicine (AASM) as follows [1]:
●Minimum duration – 0.5 seconds
●Maximum duration – 10 seconds
●Amplitude – 8 microvolt increase in EMG voltage above resting EMG
●Onset – Point at which there is an 8 microvolt increase in EMG voltage above baseline
●Ending – Start of the period lasting ≥0.5 seconds during which EMG does not exceed 2 microvolts above resting EMG
PLMS may or may not be associated with changes in electroencephalography (EEG) activity (waveform 3), including changes associated with partial or full arousals (waveform 4). EEG alterations occurring in the context of PLMS may include K complexes, K-alpha complexes, brief bursts of alpha activity or other cortical/subcortical arousals [2].
PLMS can appear immediately with the onset of non-rapid eye movement (NREM) stage 1 (N1) sleep, but they are more frequent during NREM stage 2 (N2) sleep and usually decrease in frequency during NREM stage 3 (N3) sleep. They are typically absent or at their lowest frequency during REM sleep [3].
PLMS are reported as a total number across the night, as an index (number per hour of sleep: PLMS x 60/total PSG sleep time in minutes), and by the total PLMS associated with arousals (table 2) [1]. Many centers further break down leg movement count by stage of sleep (NREM and REM sleep) and total sleep time. Of note, there are few data to suggest that PLMS associated with an arousal are of any greater clinical significance than PLMS without arousal.
Not all leg movements during PSG constitute PLMS. Some leg kicks are either too long (waveform 5) or too short (waveform 6) to qualify as PLMS. Depending on the clinical context, shorter leg movements may represent excessive fragmentary myoclonus or foot tremor, and longer movements may be leg cramps. (See 'Excessive fragmentary myoclonus' below and 'Sleep-related leg cramps' below.)
The clinical significance of PLMS is controversial. PLMS can be nonspecific and may be observed in healthy individuals as benign, sporadic episodes of involuntary leg movements that occur during sleep. PLMS in isolation (ie, not associated with another sleep or medical disorder) are being investigated for a potential association with underlying or future cardiovascular risk, but the evidence regarding the presence and directionality of this relationship remains mixed but a focus of ongoing research [4-6]. PLMS can also be seen in the context of sleep disorders such as untreated sleep apnea (waveform 7) or narcolepsy, and can represent a potential marker for other primary sleep disorders like restless legs syndrome (RLS) or periodic limb movement disorder (PLMD). (See "Clinical features and diagnosis of restless legs syndrome and periodic limb movement disorder in adults", section on 'Periodic limb movements of sleep'.)
We generally consider PLMS to be a marker of potential risk for conditions such as RLS and suggest that adult patients with a PLMS index >15 events/hour (>5 events/hour for children) be evaluated for secondary etiologies, including [3]:
●RLS
●PLMD
●Inadequately-treated sleep apnea
●Medications (eg, selective serotonin reuptake inhibitors and serotonin norepinephrine reuptake inhibitors)
●Iron deficiency
●Peripheral neuropathy
●Renal insufficiency
Treatment should NOT be initiated exclusively based on the reporting of PLMS on a sleep study but instead in conjunction with the clinical presentation [7]. (See "Clinical features and diagnosis of restless legs syndrome and periodic limb movement disorder in adults", section on 'Diagnosis' and "Restless legs syndrome and periodic limb movement disorder in children", section on 'Diagnosis'.)
Sleep-related leg cramps — Sleep-related leg cramps are painful sensations that occur in the calf or the small muscles of the foot due to sudden and intense involuntary muscle contractions resulting in muscle spasms, often lasting several seconds to minutes.
While a sleep study is not needed to diagnose sleep-related leg cramps, they occasionally occur during PSG performed for other reasons. They appear as nonperiodic bursts of the gastrocnemius on EMG without any associated physiological changes during sleep (waveform 8) [3]. Sleep-related leg cramps can occur during any sleep stage.
Compared with other leg movements of sleep, the critical differentiating feature of sleep-related leg cramps is the actual spasm or hardening of the muscle that occurs during the painful event (which can be assessed by the technician at the time of the study). Leg cramp "events" are much briefer than the typical symptoms of other disorders such as RLS, which usually last for hours [3,8].
Nocturnal leg cramps are a clinical diagnosis based on typical symptoms and exclusion of other causes of muscle cramping and disorders that may mimic leg cramps, such as RLS, PLMD, and peripheral neuropathy. Their presence on PSG is important to document, as frequent leg cramps may lead to sleep disruption and/or insomnia. (See "Nocturnal leg cramps".)
Sleep-related bruxism — Bruxism refers to repetitive jaw-muscle activity characterized by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible.
Sleep-related bruxism has distinct morphologic features on PSG (waveform 9). A bruxism episode can vary from a sustained tonic contraction to a phasic burst, with an increase in muscle potential (>20 percent of the maximal voluntary activity while awake) lasting ≥0.5 seconds with an inter-movement interval of >3 seconds [9].
In order to detect bruxism, the standard PSG may include additional EMG derivations, with surface electrodes placed over bilateral masseter and temporal muscles, sometimes even on the frontal muscles. Audio-video collected data also help to confirm the nature of the sounds (eg, grinding, snoring) and the type of movements (eg, sigh, swallowing, coughing). Bruxism can also be scored exclusively with the demonstration of two audible tooth grinding episodes per night in patients without history of epilepsy [1].
The muscle potential increase observed on PSG must be differentiated from a variety of movements that can often be mistaken for bruxism:
●Simple body or head movements
●Myoclonus, which are periodic short muscle contractions during sleep
●Head banging, head rolling, or other rhythmic movements of the head (figure 2B); such movements occasionally occur at a frequency of about 1 Hz, which is within the range of bruxism
●Other rhythmic oromandibular activities (eg, sleep chewing (waveform 10))
The intensity and duration of sleep-related bruxism is quite variable, but it often occurs hundreds of times during a sleep period. Bruxism may occur in association with a respiratory event (eg, an obstructive apnea), either before or after, and typically improves once the sleep apnea is properly treated.
There are no standard criteria for reporting of bruxism episodes, but reporting is recommended especially if the bruxism events are associated with sleep disruption or other sleep disruptive events, including sleep apnea.
PSG is not required to diagnose sleep-related bruxism. The clinical diagnosis of sleep-related bruxism is reviewed separately. (See "Sleep-related bruxism (tooth grinding)".)
Sleep-related rhythmic movements — Sleep-related rhythmic movements are characterized by repetitive, stereotyped, and rhythmic motor behaviors. The motor manifestations primarily involve either body rocking, head banging, or head or body rolling from side to side (figure 2A-B and waveform 11).They can be witnessed during quiet wakeful activities or during sleep initiation, presumably as a self-soothing ritual. These movements are specifically distinguished from tremors, which are defined as a rhythmic and involuntary movement of any body part.
Formal PSG criteria include a defined frequency range of 0.5 to 2.0 Hz, with at least four defined movements representing an established "cluster" of rhythmic movements [1]. Video PSG studies indicate that nearly one-half of all rhythmic movements occur during N1 or N2 sleep exclusively, one-third of cases occur throughout both NREM and REM sleep, and one-quarter occur exclusively during REM sleep [3]. Rhythmic movements exclusive to REM sleep occur more frequently in adults.
In most cases, the movements are not associated with significant consequences and are considered developmentally normal. They occur commonly in infants and young children and generally resolve spontaneously by the age of five [1]. When they interfere with normal sleep or daytime function, or result in self-harm or injury, they are classified as sleep-related rhythmic movement disorder (RMD). RMD is a clinical diagnosis and does not require PSG. (See "Sleep-related movement disorders in childhood", section on 'Rhythmic movement disorder'.)
Benign sleep myoclonus of infancy — Benign sleep myoclonus of infancy, also called benign neonatal sleep myoclonus, is characterized by repetitive myoclonic jerks during sleep in infants from birth to six months of age [3].
On PSG, the movements tend to be bilateral and massive, involving large muscle groups, and can occur in the whole body or only in the limbs, the trunk, and sometimes even the face. There is paroxysmal muscle activity without ictal or interictal EEG abnormalities. Muscle jerks are typically seen in clusters of four or five jerks per second, each jerk lasting 40 to 300 milliseconds [3]. The jerks are not associated with arousals, awakenings, or sleep stage transitions. They occur exclusively in sleep and stop when the infant is aroused.
The clinical diagnosis of benign sleep myoclonus of infancy is made when there are repetitive myoclonic jerks involving the limbs, trunk, or whole body in an infant of the appropriate age (eg, birth to six months of age), in the absence of a better explanation for the symptoms (eg, medications or another sleep, medical, or neurologic disorder) [3]. Symptoms may be present for only a few days or may last for several months. The disorder is benign but important to recognize, as it is often confused with epilepsy and may be inappropriately treated with antiseizure medications. (See "Nonepileptic paroxysmal disorders in infancy", section on 'Benign neonatal sleep myoclonus'.)
Propriospinal myoclonus at sleep onset — Propriospinal myoclonus at sleep onset (ie, spinal myoclonus, plurisegmental myoclonus, intersegmental myoclonus, axial myoclonus) is a rare disorder, characterized by jerks involving the abdominal and truncal muscles occurring at the transition from wakefulness to sleep [3]. Similar to RLS, these movements appear to be related to the recumbent position and a state of relaxed wakefulness.
When captured on PSG, propriospinal myoclonus is characterized by brief myoclonic EMG bursts recurring nonperiodically (waveform 12). EEG typically shows an alpha rhythm without corresponding epileptiform discharges. The movements disappear with mental activation and with the onset of a stable sleep stage.
The clinical diagnosis is based on the presence of sudden jerks, mainly of the abdomen, trunk, and neck during relaxed wakefulness and drowsiness, as the patient attempts to fall asleep [3]. Diagnostic criteria also require that the movements directly result in sleep disruption and insomnia not otherwise explained by another etiology.
Propriospinal myoclonus that persists throughout the day has been linked to spinal cord pathology in a minority of patients; however, there is no evidence that propriospinal myoclonus that is limited to sleep onset is associated with structural nervous system damage [3]. (See "Symptomatic (secondary) myoclonus", section on 'Propriospinal myoclonus'.)
Excessive fragmentary myoclonus — Excessive fragmentary myoclonus (EFM) is characterized by very small movements of the corners of the mouth, fingers, or toes, often invisible to the naked eye, usually observed during NREM sleep.
Morphologically, EMG bursts of EFM occur for at least 20 minutes during NREM sleep with at least five bursts per minute, each with a duration of approximately 150 milliseconds (waveform 13) [1]. EFM activity typically occurs without evidence of associated cortical arousals or alterations in the EEG. However, in the case of relatively high-amplitude EFM bursts, associated arousal-based K-complexes and/or shifts to faster EEG frequencies can be observed [10].
EFM is typically encountered as an incidental EMG finding and has not been associated with any negative clinical sequelae. It may be more common in adult men and in those with comorbid sleep apnea, narcolepsy, PLMD, and insomnia [1,11].
Alternating leg muscle activation — Alternating leg muscle activation (ALMA) is a term used to describe series of EMG bursts in one leg after the other during sleep [12]. Unlike PLMS, which are usually separated by 20- to 40-second intervals, individual muscle activations in ALMA approximate the frequency of muscle activation seen in human locomotion.
ALMA are defined by muscle activations that each have a duration of 100 to 500 milliseconds (much shorter than PLMS), with a frequency range for the alternating EMG bursts of 0.5 to 3.0 Hz. A single ALMA episode represents at least four muscle activations that alternate between the legs (waveform 14).
Most individuals are unaware of the movements, and their clinical impact is unknown.
Hypnagogic foot tremor — Hypnagogic foot tremor is rhythmic movement of the feet or toes that occurs at the transition between wake and sleep or during light sleep [3].
Formal criteria stipulate that at least four EMG bursts, 250 to 1000 milliseconds in duration, must occur in a frequency range series between 0.3 and 4.0 Hz (waveform 15).
Hypnagogic foot tremor appears to be a common and benign PSG finding [3]. There are no clinical consequences, and treatment consists of patient education on the diagnosis and the benign nature of the movements.
Hypnic jerks (sleep starts) — Hypnic jerks, also known as sleep starts, are sudden, brief, simultaneous contractions of the body or one or more body segments occurring at sleep onset (figure 3). They occur at the wake-sleep transition and usually consist of a single contraction that often affects the body asymmetrically [3]. The jerks may be spontaneous or induced by stimuli.
PSG recordings may reveal a hypnic jerk during the transition from wakefulness to sleep, and mainly at the beginning of the sleep episode. Multiple jerks occasionally occur in succession, usually early in the sleep period. Superficial EMG recordings of the involved muscles show brief high-amplitude potentials, generally 75 to 250 milliseconds in duration. The EEG typically shows drowsiness or stage N1 sleep patterns (waveform 16).
The motor activity is often associated with a sensory, auditory, or visual component. The individual may not recall the jerk if it does not result in an awakening. Hypnic jerks are common and often related to sleep deprivation. When frequent, intense, or repetitive, they may result in insomnia. (See "Approach to abnormal movements and behaviors during sleep", section on 'Simple or single movements'.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Parasomnias, hypersomnias, and circadian rhythm disorders".)
SUMMARY
●Sleep-related movements are commonly seen during polysomnography (PSG) and are often benign. They are usually encountered incidentally when PSG is being performed for another indication. However, some movements warrant further investigation when they negatively impact sleep quality, resulting in daytime symptoms or injury. The clinical evaluation of abnormal movements during sleep is presented separately. (See "Approach to abnormal movements and behaviors during sleep".)
●Examples of sleep-related movements and their polysomnographic characteristics include the following:
•Periodic limb movements of sleep (waveform 2) (see 'Periodic limb movements of sleep' above)
•Sleep-related leg cramps (waveform 8) (see 'Sleep-related leg cramps' above)
•Sleep-related bruxism (waveform 9) (see 'Sleep-related bruxism' above)
•Sleep-related rhythmic movements (waveform 11) (see 'Sleep-related rhythmic movements' above)
•Benign sleep myoclonus of infancy (see 'Benign sleep myoclonus of infancy' above)
•Propriospinal myoclonus at sleep onset (waveform 12) (see 'Propriospinal myoclonus at sleep onset' above)
•Excessive fragmentary myoclonus (waveform 13) (see 'Excessive fragmentary myoclonus' above)
•Alternating leg muscle activation (waveform 14) (see 'Alternating leg muscle activation' above)
•Hypnagogic foot tremor (waveform 15) (see 'Hypnagogic foot tremor' above)
•Hypnic jerks (waveform 16) (see 'Hypnic jerks (sleep starts)' above)
