Movement Disorders Moment: Sleep-Related Movement Disorders—A Review

Sleep specialists often devote substantial work time to the evaluation and management of sleep-disordered breathing, given the prevalence and treatability of obstructive sleep apnea (OSA). Including OSA, 58 sleep disorders, not including isolated symptoms and normal variants, are described in the International Classification of Sleep Disorders, Third Edition, Text Revision (ICSD-3-TR).¹ This article reviews a category of sleep disorders known as sleep-related movement disorders (SRMDs). 

Sleep-Related Movement Disorders

The following 10 SRMDs are formally recognized in the ICSD-3-TR:¹

• Restless legs syndrome (RLS)
• Periodic limb movement disorder (PLMD)
• Nocturnal muscle cramps
• Sleep-related bruxism
• Sleep-related rhythmic movement disorder
• Benign sleep myoclonus of infancy
• Propriospinal myoclonus at sleep onset
• Sleep-related movement disorder due to a medical disorder
• Sleep-related movement disorder due to a medication or substance
• Sleep-related movement disorder, unspecified
• Isolated symptoms and normal variants include hypnogogic foot tremor, alternating leg muscle activation, and sleep starts (hypnic jerks). 

Sleep disorders presenting primarily as physical movements are divided into 2 major categories: parasomnias and SRMDs. These disorder types differ substantially in clinical consequences and treatment modalities. The primary differences in symptoms and clinical presentation between parasomnias and SRMDs are listed in Table 1. Parasomnias are defined in the ICSD-3-TR as “undesirable physical events or experiences that occur during entry into sleep, within sleep, or during arousal from sleep,” and include rapid eye movement (REM) behavior disorder (in which one physically enacts dreams) and various non-REM phenomena (ie, disorders of arousal, which include sleepwalking, confusional arousals, sleep-related eating disorder, and sleep terrors).¹ Parasomnias present with complex, nonstereotyped behavioral movements. In contrast, SRMDs consist of simpler, more stereotyped movements, often predictable in timing and clinical presentation and often disrupting or delaying sleep. 

Recognition of SRMDs is important for neurologists and sleep specialists. SRMDs present as primary complaints, secondary symptoms, or incidental observations of a bed partner. Sudden cortical arousals, regardless of cause, are often associated with nonspecific body movements that might be difficult to distinguish from SRMDs. In addition, symptoms of SRMDs can mimic those of neurologic disorders such as epileptic seizures or myoclonus and may occur during sleep or while awake. Some seizures that occur while the individual is awake, such as focal impaired consciousness seizures, may resemble parasomnias; others, such as those associated with sleep-related hypermotor epilepsy, may resemble SRMDs. Basic clinical distinctions between SRMDs and seizures are listed in Table 2. 

Descriptions of Specific SRMDs

Restless Legs Syndrome

The most widely known SRMD is RLS, in which limb (usually leg) discomfort is accompanied by a strong urge to move, manifesting as repetitive kicking, stretching, or moving the legs. The leg movements temporarily improve the discomfort which returns when the movements stop. Often the discomfort is difficult for the individual to describe, with terms such as “unpleasant” or “creepy-crawly” commonly used to describe the sensation. RLS symptoms occur during wakefulness, typically in the evening.

RLS is common, with clinically significant symptoms occurring in 2% to 3% of adults in the United States and Europe.² RLS is both a neurologic movement disorder and an intrinsic sleep disorder; because it often occurs predictably at night, RLS causes difficulties with initiating and maintaining sleep, affecting both the individual and the bed partner. RLS occurs more frequently in the setting of a family history, pregnancy, iron deficiency, and renal disease. Multiple sclerosis and Parkinson disease are commonly associated with RLS; other associations may include migraine and peripheral neuropathy. Multiple potential triggers may exacerbate RLS symptoms and should be avoided or addressed, including certain medications (Table 3), alcohol use, and caffeine intake.

Earlier this year, the American Academy of Sleep Medicine (AASM) published an updated clinical practice guideline regarding the management of RLS based on a task force comprehensive review of relevant literature.³ This publication features several important recommendation changes compared with the 2012 AASM practice parameter for RLS. 

First, alpha-2 ligand medications (gabapentin, pregabalin, and gabapentin enacarbil) now represent first-line therapy for people with RLS without iron deficiency, with strong recommendations made for their use. Conditional recommendations were made against the use of dopamine agonists (pramipexole, ropinirole, and transdermal rotigotine)—previously strongly recommended medications—due to concerns regarding augmentation associated with long-term use.³

The new practice guideline also emphasizes the importance of iron supplementation in the event of low brain iron levels reflected by iron studies. Serum iron testing was recommended for all individuals with clinically significant RLS, including ferritin and transferrin saturation. Strong recommendations were given for the use of intravenous (IV) ferric carboxymaltose in people with appropriate iron status; conditional recommendations were given for the use of IV low-molecular-weight iron dextran, IV ferumoxytol, and oral ferrous sulfate. The AASM suggested iron supplementation in adults with RLS with oral or IV iron for serum ferritin levels ≤75 ng/mL or transferrin saturations <20% and with IV iron for ferritin levels between 75 and 100 ng/mL. For children, oral or IV iron supplementation was recommended for ferritin levels <50 ng/mL. 

In addition, the guideline now confers a conditional recommendation on the use of bilateral high-frequency peroneal nerve stimulation in adults with RLS. Conditional recommendations were also given for the use of dipyridamole, extended-release oxycodone, and other opioids. The guideline suggested against the use of bupropion, carbamazepine, clonazepam, valerian, or valproic acid, and strongly recommended against cabergoline use. 

Periodic Limb Movement Disorder

Periodic limb movements in sleep (PLMS) are common incidental findings clinically and polysomnographically, particularly in older individuals and in people with RLS. PLMS may also occur in higher prevalence in individuals with narcolepsy, REM behavior disorder, and OSA.⁴ If PLMS cause substantial sleep disturbance or functional impairment (such as daytime somnolence, mood problems, or behavioral issues), they rise to the level of a disorder. PLMD consists of repetitive, stereotyped, often jerky or twitchy limb movements solely occurring during sleep, causing sleep fragmentation due to cortical arousals. 

PLMD is less common than RLS. Establishing a causal relationship between PLMS and clinical symptoms can be challenging. Unlike RLS, which is diagnosed clinically without diagnostic sleep study testing, PLMD requires polysomnographic confirmation in sleep as defined by the latest version of the official AASM scoring manual.⁵ The quantitative polysomnographic criteria for PLMD are >5/h in children and >15/h in adults. Historically, L-dopa and dopamine agonists have been considered to be first-line treatment for PLMD.⁶

The degree to which PLMS alone should be treated has been controversial. Low brain iron levels may be associated with PLMS in the presence of RLS, but the potential relationship between ferritin levels and PLMD without RLS is unclear. The recent AASM RLS guideline³ does not make recommendations for treatments for PLMD but suggests against triazolam or valproic acid use. 

Nocturnal Muscle Cramps

Nocturnal muscle cramps are painful, involuntary, and briefly sustained muscle contractions, usually occurring in calf and foot muscles. Sleep is often delayed or disrupted due to the discomfort. Such cramps are common, particularly in older individuals. The sustained nature of the contractions and resulting pain distinguish these events from PLMS. Nocturnal muscle cramps are associated with medications (such as beta agonists), pregnancy, several metabolic disorders, and plantar foot flexion.⁷

Consistently effective treatments are lacking. Using hot packs and stretching or massaging the cramping muscle may relieve symptoms. Quinine has been discouraged by the Food and Drug Administration as a cramp treatment due to concerning side effects, including thrombocytopenia and QT prolongation.⁷

Sleep-Related Bruxism

Sleep-related bruxism refers to repetitive grinding or clenching of the teeth during sleep, causing dental problems, headaches, and jaw muscle discomfort. The prevalence is highest in children and decreases with increasing age. A sleep study may reveal masseter and temporalis muscle contractions during sleep; however, in-laboratory polysomnography is not usually required to make a diagnosis. The use of mouthguards and botulinum toxin injections may be helpful.¹

Sleep-Related Rhythmic Movement Disorder

Sleep-related rhythmic movement disorder involves stereotyped, rhythmic physical movements during drowsiness or sleep, often consisting of repetitive head-banging, truncal rocking movements, or other movements involving large body muscles, sometimes accompanied by rhythmic vocalizations. The repetitive movements usually maintain a frequency of 0.5 to 2 Hz.⁸ Although sleep-related rhythmic movement disorder is more prevalent in children, adults may also exhibit these movements. Many young children may exhibit repetitive or rhythmic movements, but these do not represent a disorder in absence of associated problems (such as sleep disruption, functional impairment, or physical injury). Although potentially helpful in complicated cases, overnight polysomnography is not required to make a diagnosis. 

Benign Sleep Myoclonus of Infancy

“Benign sleep myoclonus of infancy” refers to repetitive myoclonic jerks of the limbs or trunk exclusively during sleep in infants terminating abruptly upon arousal. As indicated by the name of the disorder, the clinical course is benign and brief, usually resolving within 1 year without long-term sequelae.¹

Propriospinal Myoclonus at Sleep Onset

Propriospinal myoclonus at sleep onset, which usually affects adults, consists of jerking movements of the trunk or neck during drowsiness, causing difficulty sleeping. Propriospinal myoclonus at sleep onset is rare. The movements, which may also occur while the individual is relaxed and awake, are often isolated and not rhythmic, unlike in other SRMDs. Polysomnography is useful in making a diagnosis.¹

Isolated Symptoms and Normal Variants

In addition to SRMDs due to medical conditions, medications, or substance use, and unspecified SRMDs, the following isolated symptoms and normal variants are recognized by ICSD-3-TR: excessive fragmentary myoclonus, hypnagogic foot tremor and alternating leg muscle activation, and sleep starts (hypnic jerks).¹ Hypnic jerks—sudden jerks of the body or large body segments occurring at sleep onset, which are more prevalent during periods of sleep deprivation—are common. They may or may not be recalled. For some individuals, they may be distressing or concerning, but the clinical course is usually benign. These events may improve or resolve with regular bedtime schedules, consistent sleep satiety, reduction of caffeine intake, and stress level management. 

Restless Sleep Disorder

As sleep medicine advances, additional sleep disorders are identified. Restless sleep disorder, recently recognized in children, is characterized by excessive large-muscle movements that occur exclusively during sleep and are associated with daytime consequences (eg, daytime somnolence, behavioral problems).⁹ A frequent association with low ferritin levels in affected children suggests a potential link with RLS. 

Conclusions

SRMDs—which should be distinguished from various mimics, such as parasomnias, epileptic seizures, and other neurologic movement disorders—represent an important category of intrinsic sleep disorders. Some SRMDs may have a higher prevalence in individuals with neurologic disorders. RLS is a common and treatable SRMD, and standards for its management have evolved in recent years. Most SRMDs can be diagnosed clinically without the need for in-laboratory polysomnography. However, diagnostic polysomnography can be helpful to characterize the nature of the movements—particularly if unwitnessed or otherwise difficult to describe—and the degree to which they may be associated with sleep fragmentation. A formal sleep medicine clinic evaluation may be useful in determining the extent to which the individual may have an intrinsic sleep disorder.