A young woman with sleep-disruptive “twitching”

A 20-year-old patient was referred for evaluation of twitching during sleep. She was adopted; at age 2 years, developmental delay was noted, and at age 5 years she was diagnosed with attention deficit-hyperactive disorder. Dexmethylphenidate was prescribed, but she developed tics, including neck-thrusting, shoulder-rolling, hip twisting, lip smacking, and myoclonic jerking in sleep. This medication was stopped with resolution of symptoms until 2 years ago, when twitching in sleep was again seen. Because of nonrestorative sleep, evaluation was sought.

She underwent an electroencephalogram (EEG), which was normal during wakefulness and sleep. A brain magnetic resonance image was unremarkable. Melatonin 5 mg was started for chronic sleep-onset insomnia, but she continued to experience “jolts” in sleep.

She was referred to the Sleep Center. Her mother described the twitches as recurrent, occurring in a single body part (neck, torso, arm, legs) and happening in the early morning hours, after 2 am. There were no history or exam findings consistent with upper airway obstruction, restless legs syndrome, dream enactment, or narcolepsy, except for an excessive sleep time. She slept an average of 12 hours without feeling refreshed. She was referred for a video EEG and polysomnogram (PSG).

Her video EEG was normal with no epileptiform abnormalities. Representative samples of the key PSG findings are shown in Figure 1 (with the abnormality highlighted in a blue box) and Video S1 ^{(6.5MB, mp4)} in the supplemental material ^{(23.8KB, pdf)} . Total sleep time was 584.5 minutes, with all sleep stages represented; sleep efficiency was 86.5%. Sleep latency was 32.8 minutes; rapid eye movement (REM) latency was 107.5 minutes. The apnea-hypopnea index and respiratory disturbance index were both 0.8; O₂ nadir was 93%. Periodic limb movement Index was 3.8. Periodic limb movement Index with arousals was 1.1.

Figure 1. Thirty-second-epoch REM sleep stage.

Blue boxes show episodes of neck myoclonus. Red brackets show arousal. Electroencephalogram (EEG) and electro-oculogram (EOG) referenced to left mastoid (M1) and right mastoid (M2) electrodes. Chest = Chest belt; CHIN1-CHIN2 = chin surface electromyogram (EMG) electrode; ECGL-ECGR = electrocardiogram; EEG = F3-M2 (left frontal electrode), F4-M1 (right frontal electrode), C3-M2 (left central electrode), C4-M1 (right central electrode), O1-M2 (left occipital electrode), O2-M1 (right occipital electrode); EOG = LOC-M2, left eye; ROC-M1, right eye; EtCO2 capnograph = end tidal carbon dioxide; Flow = thermistor; L-ARM = left arm surface EMG; LAT1-LAT2 = left anterior tibialis surface EMG; OSAT = oxygen saturation; Pflow = pressure flow; Pleth = plethysmograph, measure of oxygen related to blood flow fluctuation; PR = heart rate; R-ARM = right arm surface EMG; RAT1-RAT2 = right anterior tibialis surface EMG; Snore = Snore channel; Sum = summary of belt and abdominal belts signal; TcCO2 = transcutaneous carbon dioxide.

QUESTION: What is causing this patient’s sleep-related twitches and the PSG abnormality seen above?

ANSWER: Frequent neck myoclonus (myoclonic jerks)

DISCUSSION

Frequent myoclonic jerks were noted, mostly in the neck, all in REM sleep. The average rate of neck myoclonus was 72 per hour (1.3 per minute; maximum 4 per minute) of REM sleep. A total of 43.7% were associated with arousals, of which there were 80 (all in REM sleep). (Arousal index per hour of sleep was 23.4; 19.4/h in non-REM sleep, 35.6/h in REM stage sleep.) There was no association with periodic limb movements, respiratory events, or involved other body movements.

Myoclonic jerks are considered a benign sleep phenomenon; frequent jerks are thought to be associated with underlying sleep or neurologic disorders such as obstructive sleep apnea, parasomnia, or epilepsy. Recent research suggests, however, that myoclonic jerks may actually be a primary REM sleep-related movement disorder resulting in nonrestorative sleep and other clinical consequences such as neck pain and stiffness, especially at higher rates per hour.

Frauscher et al¹ found that 54.6% of 205 consecutive patients undergoing PSG had neck myoclonus during REM sleep; mean frequency was 1.0 ± 2.7 events/h of REM sleep. Twenty percent of events were followed by arousals; there were no significant differences in the frequency of common sleep disorders between patients with and without neck myoclonus.¹

High rates of myoclonic-associated arousal have also been reported by Pujol et al² (50%; 1.18 per hour, mostly in REM sleep, 50% of jerks were associated with other body movements), Wolfensberger et al³ (80%; 79.7% in REM sleep), and Lopez et al⁴ (65.2%; 38.1% were associated with leg movements, only 9.6% with respiratory events). Lopez and colleagues reported 30 patients with an excessive myoclonic jerks, defined as > 30 per hour of REM sleep, and found that these patients may present with sleepiness or nonrestorative sleep. Additionally, it was reported that cortical arousals occurred simultaneously or just after the sleep-related jerks,⁴ which differs from periodic limb movements in restless legs syndrome,⁵ suggesting a different pathogenesis for myoclonic jerks than typical periodic limb movements. As with periodic limb movements, patients may not be aware of their neck movements, requiring collateral history to raise suspicion (and PSG for diagnosis).

SLEEP MEDICINE PEARLS

1. Frequent myoclonic jerks including neck myoclonus may be a primary sleep-related movement disorder resulting in nonrestorative sleep, especially at higher rates and associated with arousals.

2. Myoclonic jerks typically occur in REM sleep and may not be related to other sleep-related disorders.

3. Clonazepam has been associated with suppression of myoclonic jerks;¹ administration of this medication (0.5 mg every night at bedtime was prescribed for this patient, which resulted in fewer events and feeling more refreshed upon awakening, no follow-up PSG was obtained yet; higher doses led to oversedation) may result in symptom improvement or resolution.

DISCLOSURE STATEMENT

All authors have seen and approved this manuscript. Work for this study was performed at the NYU Langone Health Comprehensive Epilepsy Center–Sleep Center, 724 Second Avenue, New York, NY 10016. The authors report no conflicts of interest.