Excessive fragmentary myoclonus: time of night and sleep stage distributions

A reliable automatic algorithm to score fragmentary myoclonus

Excessive fragmentary myoclonus (EFM) is an incidental polysomnographic finding requiring documentation of ≥20 minutes of NREM sleep with ≥5 fragmentary myoclonus (FM) potentials per minute. Manual FM scoring is time-consuming and prone to inter-rater variability. This work aimed to validate an automatic algorithm to score FM in whole-night recordings. One expert scorer manually scored FM in the anterior tibialis muscles in 10 polysomnographies of as many subjects. The algorithm consisted of two steps. First, parameters of the automatic leg movement identification algorithm of the BrainRT software (OSG, Belgium) were modified to identify FM-like activity. Second, a post-processing algorithm was implemented to remove FM activity not meeting sufficient amplitude criteria. The parameter choice and the post-processing were optimised with leave-one-out cross-validation. Agreement with the human scorer was measured with Cohen's kappa (k) and correlation between manual and automatic FM indices in different sleep stages was evaluated. Agreement in identifying patients with EFM was computed. The algorithm showed substantial agreement (average k > 0.62) for all sleep stages, except for W, where a moderate agreement was observed (average k = 0.58). Nonetheless, the agreement between human scorer and the algorithm was similar to previously reported values of inter-rater variability for FM scoring. Correlation coefficients were over 0.96 for all sleep stages. Furthermore, the presence/absence of EFM was correctly identified in 80% of the subjects. In conclusion, this work presents a reliable algorithm for automatic scoring of FM and EFM. Future studies will apply it to objectively and consistently evaluate FM indices and the presence of EFM in large populations.

The Parasomnias and Sleep Related Movement Disorders—A Look Back at Six Decades of Scientific Studies

The objective of this article is to provide a comprehensive personal survey of all the major parasomnias with coverage of their clinical presentation, investigation, physiopathogenesis and treatment. These include the four major members of the slow-wave sleep arousal parasomnias which are enuresis nocturna (bedwetting), somnambulism (sleepwalking), sleep terrors (pavor nocturnus in children, incubus attacks in adults) and confusional arousals (sleep drunkenness). Other parasomnias covered are sleep-related aggression, hypnagogic and hypnopompic terrifying hallucinations, REM sleep terrifying dreams, nocturnal anxiety attacks, sleep paralysis, sleep talking (somniloquy), sexsomnia, REM sleep behavior disorder (RBD), nocturnal paroxysmal dystonia, sleep starts (hypnic jerks), jactatio capitis nocturna (head and total body rocking), periodic limb movement disorder (PLMs), hypnagogic foot tremor, restless leg syndrome (Ekbom syndrome), exploding head syndrome, excessive fragmentary myoclonus, nocturnal cramps, and sleep-related epileptic seizures. There is interest in the possibility of relationships between sleep/wake states and creativity.

Fragmentary Hypnic Myoclonus and Other Isolated Motor Phenomena of Sleep

Excessive fragmentary hypnic myoclonus, hypnic jerks, hypnagogic foot tremor, alternating leg muscle activation, and sleep-related cramps are less known sleep-related motor disorders (SRMDs). These manifestations are frequently missed or misinterpreted polygraphic findings that can be frequently confused with the more frequent SRMDs. These symptoms can present as isolated motor symptoms but can be also the cause of otherwise cryptogenic insomnias and somnolence. Expanding the knowledge on these isolated symptoms and defining their polygraphic and clinical features are essential for their identification. However, clear cut-offs to discern between the isolated phenomenon and the disorder are still to be found.

Excessive Fragmentary Myoclonus: What Do We Know?

Excessive fragmentary myoclonus (EFM) is a polysomnographic finding registered by the surface electromyography (EMG) and characterized as a result of the muscle activity consisting of sudden, isolated, arrhythmic, asynchronous and asymmetric brief twitches. The EMG potentials are defined by the exact criteria in The International Classification of the Sleep Disorders, 3rdedition and they appear with high intensity in all sleep stages. Clinical significance of EFM is unclear. It was observed in combination with other diseases and features such as obstructive and central sleep apnea, narcolepsy, periodic limb movements, insomnia, neurodegenerative disorders and peripheral nerve dysfunction. Relation to such wide range of diseases supports the opinion that EFM is nor a specific sleep disorder nor a specific polysomnographic sign. The option that EFM is a normal variant has also not been ruled out so far.

Peripheral nerve function in patients with excessive fragmentary myoclonus during sleep

OBJECTIVES

Excessive fragmentary myoclonus is a frequent incidental finding in patients undergoing polysomnography for other reasons. The aim of this study was to evaluate whether electrophysiological examination in patients with excessive fragmentary myoclonus during sleep according to American Academy of Sleep Medicine (AASM) criteria shows findings of peripheral nerve dysfunction.

METHODS

Ninety-eight of 100 patients with excessive fragmentary myoclonus detected as an incidental finding during routine polysomnography underwent electrophysiological workup. Motor nerve conduction studies of the right peroneal and tibial nerves, F-wave recordings of the tibial nerve, antidromic sensory nerve conduction studies of the left sural nerve and needle electromyography of the right tibialis anterior muscle were performed and classified as normal, peripheral neuropathy, lumbar 5 (L5) nerve root lesion, or benign fasciculations.

RESULTS

Fifty percent (49 out of 98) presented with electrophysiological abnormalities, most frequently polyneuropathy (32 out of 49, 65.3%), followed by L5 nerve root lesions (13 out of 49, 26.5%) and benign fasciculations (4 out of 49, 8.2%). Patients with electrophysiological abnormalities were older than those without.

CONCLUSIONS

The high prevalence of abnormal neurophysiological findings in patients with excessive fragmentary myoclonus during polysomnography suggests that excessive fragmentary myoclonus during sleep according to AASM criteria is not primarily a sleep-related phenomenon, but only persists during sleep and points to peripheral nerve pathology at least in part of the cases. Patients with incidental EFM during polysomnography should undergo electrophysiological workup for peripheral nerve pathology.

Motor events during healthy sleep: a quantitative polysomnographic study

STUDY OBJECTIVES

Many sleep disorders are characterized by increased motor activity during sleep. In contrast, studies on motor activity during physiological sleep are largely lacking. We quantitatively investigated a large range of motor phenomena during polysomnography in physiological sleep.

DESIGN

Prospective polysomnographic investigation.

SETTING

Academic referral sleep laboratory.

PARTICIPANTS

One hundred healthy sleepers age 19-77 y were strictly selected from a representative population sample by a two-step screening procedure.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Polysomnography according to American Academy of Sleep Medicine (AASM) standards was performed, and quantitative normative values were established for periodic limb movements in sleep (PLMS), high frequency leg movements (HFLM), fragmentary myoclonus (FM), neck myoclonus (NM), and rapid eye movement (REM)-related electromyographic (EMG) activity. Thirty-six subjects had a PLMS index > 5/h, 18 had a PLMS index > 15/h (90th percentile: 24.8/h). Thirty-three subjects had HFLM (90th percentile: four sequences/night). All subjects had FM (90th percentile 143.7/h sleep). Nine subjects fulfilled AASM criteria for excessive FM. Thirty-five subjects had NM (90th percentile: 8.8/h REM sleep). For REM sleep, different EMG activity measures for the mentalis and flexor digitorum superficialis muscles were calculated: the 90th percentile for phasic mentalis EMG activity for 30-sec epochs according to AASM recommendation was 15.6%, and for tonic mentalis EMG activity 2.6%. Twenty-five subjects exceeded the recently proposed phasic mentalis cutoff of 11%. None of the subjects exceeded the tonic mentalis cutoff of 9.6%.

CONCLUSION

Quantification of motor phenomena is a basic prerequisite to develop normative values, and is a first step toward a more precise description of the various motor phenomena present during sleep. Because rates of motor events were unexpectedly high even in physiological sleep, the future use of normative values for both research and clinical routine is essential.

Manual quantitative assessment of amplitude and sleep stage distribution of excessive fragmentary myoclonus

INTRODUCTION

Excessive fragmentary myoclonus (EFM) consists of brief, asynchronous, twitch-like movements appearing asymmetrically in sleep. The new AASM Manual for the Scoring of Sleep and Associated Events identifies some EFM scoring criteria but does not provide amplitude criteria for scoring EFM. Older observational series have used 50 μVs. We report data from various amplitude criteria using blinded comparisons.

METHODS

EFMs were analyzed on the polysomnograms of 8 patients (7 men and 1 woman, mean age 57 years, range: 47-79) using a standardized protocol for sensitivity, tonus threshold, impedance, amplitude measurements, and sleep stage. The first 20 minutes each of wake, Stage 1-2, SWS, and REM were analyzed. EFMs ≥ 25, ≥ 40, and ≥ 50 microvolts (μVs) in negative deflection above the baseline were counted in tibialis anterior muscle electromyography (EMG) channels bilaterally.

RESULTS

The mean EFM index per minute for wake, regardless of impedance, was: 7.19 ± 5.90 for ≥ 25 μV amplitude; 2.43 ± 2.02 for ≥ 40 μVs; and 2.08 ± 2.23 for ≥ 50 μVs. For sleep stages, the EFM index by stage and amplitude criteria used for measurements were: Stage 1-2: 7.38 ± 5.79 for ≥ 25 μVs; 3.13 ± 3.33 for ≥ 40 μVs; and 2.36 ± 2.66 for ≥ 50 μVs; SWS: 10.05 ± 8.04 for ≥ 25 μVs; 2.71 ± 3.13 for ≥ 40 μVs; and 1.38 ± 1.92 for ≥ 50 μVs; Total REM: 15.96 ± 11.32 for ≥ 25 μVs; 6.32 ± 4.25 for ≥ 40 μVs; and 3.94 ± 3.73 for ≥ 50 μVs; Phasic REM: 19.69 ± 15.45 for ≥ 25 μVs; 8.63 ± 7.06 for ≥ 40 μVs; and 5.52 ± 6.44 for ≥ 50 μVs; Non-phasic REM: 13.93 ± 11.31 for ≥ 25 μVs; 5.16 ± 3.57 for ≥ 40 μVs; and 3.20 ± 2.92 for ≥ 50 μVs.

CONCLUSION

EFM rates increase with SWS and total REM with the highest EFM rates occurring during phasic REM. EFM rates were increased across all sleep stages when impedance was > 30 KΩ.

Clinical Identification of the Simple Sleep-Related Movement Disorders

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.

Excessive fragmentary hypnic myoclonus: clinical and neurophysiological findings

BACKGROUND

Brief involuntary sleep-related twitches occurring asymmetrically throughout the body define physiologic hypnic fragmentary myoclonus. An abnormal intensification of this entity identifies excessive fragmentary hypnic myoclonus (EFHM), a 'proposed sleep disorder' in the International Sleep Disorders Classification.

METHODS

We describe two patients with EFHM, one associated with a REM behaviour disorder.

RESULTS

EFHM activity was restricted to sleep prevailing during NREM sleep stages and the second part of the night. EMG was normal and EEG-EMG back-averaging did not show any cortical potentials related to the twitches.

CONCLUSIONS

EFHM represents a pathological phenomenon which may or may not be associated with other sleep disorders. A brainstem generator explains its distribution throughout the body and the sleep stages.