Involuntary movements make up a notable percentage of the many causes of poor quality sleep. Although difficult to diagnose, these sleep-related movement disorders (SRMD) need to be identified as they may be warning signs of serious conditions such as Parkinson disease, Alzheimer’s disease, autoimmune disorders involving the nervous system, liver or kidney failure, or nutritional deficiencies.

Some SRMDs like restless legs syndrome (RLS) are well known, but less common SRMDs are often overlooked. According to Ambra Stefani, MD, a researcher in neurology and sleep medicine at The Medical University in Innsbruck, Austria, “all minor SRMDs tend to be missed (more than misdiagnosed), as they are seldom and not easy to identify in video polysomnography. For some, it is not clear what their clinical relevance is, but this doesn’t mean that they should not be identified and correctly diagnosed. A correct identification and classification would also help to increase our knowledge about them.”

Periodic Limb Movement Disorder (PLMD)

This SRMD usually involves the legs, often manifesting as triple flexion (at the knee and ankle and dorsal flexion of the hallux), persisting for 2 seconds and recurring at 5- to 90-second intervals. The arms may also be affected.1 Periodic leg movements occur during the non-REM phase of sleep, are associated with arousal, and may compromise sleep quality, which can cause poor performance during the day.2 Diagnosis is best established by video polysomnography (vPSG) recordings that show more than 5 movements/hour in children and 15/ hour in adults. If these clinical and vPSG criteria are not met the condition is diagnosed as PLM syndrome (PLMS).

More than 80% of people with RLS also have PLMS. Furthermore, PLMS is present in up to 75% of cases of narcolepsy and 70% of REM sleep behavior disorder (RBD) cases. “PLMD is a[n] SRMD which requires a thorough sleep history to be diagnosed, as the presence of PLMS and sleep disturbance in combination is not enough to make a diagnosis,” Dr Stefani noted. “RLS must be actively excluded, and PLMD cannot be diagnosed in the presence of RLS. If other symptoms are present, other sleep disorders must be investigated and actively excluded (eg, narcolepsy in case of excessive daytime sleepiness; RBD in case of high PLMS index during REM sleep and/or dream enactment).”

“SRBD may also be a cause of sleep disturbance and PLMS may be present, but a PLMD cannot be diagnosed if the PLMS is not the cause of the sleep disturbance,” Dr Stefani added. “Currently, treatment of PLMS is indicated only if a PLMD is diagnosed, and studies evaluating PLMD treatment are scarce. Dopaminergic treatment may even induce RLS in these patients. Few studies indicate possible efficacy of clonazepam and valproate on sleep quality, or of melatonin on PLMS index.”

Propriospinal Myoclonus at Sleep Onset

Propriospinal myoclonus (PSM) involves the thoracic and abdominal — and sometimes the neck — muscles and manifests at the beginning of sleep. It is followed by immediate waking, with some patients complaining of difficulty falling back to sleep.

While this is mostly a functional event, focal lesions of the spinal cord have been found on magnetic resonance imaging (MRI) in some patients. The probability of finding cord lesions is higher in patients who also present with PSM during the day. However, in this group, PSM may also have a psychogenic origin, identified by the presence of a readiness potential on electromyogram (EMG).3

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The differential diagnosis should include other jerky movement disorders. Hypnic jerks are common and innocuous, although they may cause insomnia; however, they do not follow a pattern of movement. They are commonly be accompanied by a sensation of falling or other visual, auditory, or sensory phenomena.4 The diagnosis of PLMS would be ruled out based on the repetitive jerks with a frequent pattern of triple flexion involving the legs.

Frequent PSMs interfering with sleep and leading to reduced performance during the day usually respond to treatment with clonazepam. In isolated cases, good results were reported with anticonvulsants like valproate, levetiracetam, and zonisamide.5 If the movement disorder is associated with mild cord compression by herniated disks, PMS improve after treating the spinal lesion.3

Excessive Fragmentary Myoclonus of Sleep

Excessive fragmentary myoclonus (EFM) most often involves an EMG diagnosis, consisting of potentials usually lasting <150 ms recorded at a rate of ≥5 per minute over a period of ≥20 minutes during non-REM sleep. Typically, no movements are seen, although in some patients twitching of the corners of the mouth or small movements of the fingers or toes were reported.6 These movements need to be distinguished from the possible twitching that occurs during REM sleep in the context of RBD.

Fragmentary myoclonus during sleep and wakefulness is likely common and benign.3 However, in the subgroup of patients with EFM, electrophysiologic abnormalities related to polyneuropathy and radicular nerve lesions are notably prevalent, calling for further studies to elucidate the causes of this condition.7 No treatment is required for EFM as patients are not aware of it and it does not interfere with their performance while awake.

Other Minor SRMDs

Other notable minor SRMDs include:

·Neck myoclonus, which occurs during REM sleep and results in head jerks. It is a physiologic phenomenon, but persistence of the condition may predict a future RBD.3

·Sleep bruxism may occur at sleep onset and at the return to sleep after overnight arousals. It can lead to dental or temporomandibular articulation problems. Wearing removable occlusal splints at night reduces tooth damage and relaxes the masseters.8

·Leg cramps are spontaneous, prolonged, continuous, painful muscle contractions that may indicate a calcium or magnesium deficit. In more serious scenarios, these cramps may be a sign of poor blood circulation in the legs.

Diagnosing Minor SRMDs

Diagnosing SRMDs is complex and involves taking a thorough history from the patient and the patient’s bed partner and a complete disease history, chronic medication or substance use, living conditions, and family history. In selected cases, vPSG or more disease-specific investigations are useful. The potential of the disorder for harm to self or others and the existing underlying pathology should be investigated. Dr Stefani maintains that, “To better differentiate between SRMD, in particular minor ones, it is necessary to: (a) identify more precise diagnostic criteria (eg, there should be no overlap between different minor SRMDs, or if there is an overlap, they should be included in a common category); and (b) train sleep physicians to recognize minor SRMDs and increase awareness and knowledge about them.”

References

1. Leonard J. Periodic limb movement disorder: symptoms and treatment. Medical News Today. Updated June 14, 2017. www.medicalnewstoday.com/articles/317911.php. Accessed February 1, 2019.

2. Salminen AV, Winkelmann J. Restless legs syndrome and other movement disorders of sleep-treatment update. Curr Treat Options Neurol. 2018;20(12):55.

3. Stefani A, Högl B. Diagnostic criteria, differential diagnosis and treatment of minor motor activity and less well-known movement disorders of sleep. Curr Treat Options Neurol. 2019;21(1):1.

4. Vaughn BV. Approach to abnormal movements and behaviors during sleep. UpToDate. Updated June 6, 2018. www.uptodate.com/contents/approach-to-abnormal-movements-and-behaviors-during-sleep. Accessed February 1, 2019.

5. Byun JI, Lee D, Rhee HY, Shin WC. Treatment of propriospinal myoclonus at sleep onset. J Clin Neurol. 2017;13:293-295.

6. Berry RB, Albertario CL, Harding SM, et al, for the American Academy of Sleep Medicine. The AASM manual for the scoring of sleep and associated events: rules, terminology and technical specifications. Version 2.5. Darien, IL: American Academy of Sleep Medicine; 2018.

7. Raccagni C, Löscher WN, Stefani A, et al. Peripheral nerve function in patients with excessive fragmentary myoclonus during sleep. Sleep Med. 2016;22:61.

8. Lal SJ, Weber KK. Bruxism management. StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing. Published January 2018. Updated December 27, 2018.