Obstructive sleep apnea syndrome aggravated propriospinal myoclonus at sleep onset
Article Outline
1. Introduction
A 62-year-old man was referred to our center for a 6-month history of abdominal movements during sleep. He had suffered sudden repetitive involuntary jerks of the neck and trunk during initiation of sleep and occasional awakenings during sleep because of abdominal movements. His wife reported heavy snoring and a cessation of breathing suggestive of sleep apnea. The first video-polysomnogram (video-PSG) revealed that he had an apnea/hypopnea index (AHI) of 37.5 per hour with an arousal index of 43.9 per hour and arousals caused by respiratory events which were linked to these myoclonic jerks.
The second video-PSG study was performed as a split-night PSG-continuous positive airway pressure (CPAP) titration with additional electromyographic monitoring to investigate the characteristics of the jerks.
2. Image analysis
The second video-PSG recordings showed the jerks were present during relaxed wakefulness (Fig. 1a) and the myoclonic jerks disappeared during conversations. Once sleep started, jerks resolved; however, they reappeared following arousals associated with termination of an apnic or hypopnic event (Fig. 1b) or spontaneous arousals (Fig. 1c). Each myoclonic activity lasted 200–600
ms, and jerks occurred at intervals varying from 4 to 25s, and started first in the rectus abdominis (Fig. 1d). Video-PSG findings confirmed the diagnosis of propriospinal myoclonus (PSM) at sleep onset, and it was aggravated by obstructive apnea hypopnea syndrome. In the CPAP portion of the study, the patient had AHI of 5.0 per hour with an arousal index of 20.8 per hour. The jerks completely resolved during stable sleep along with the elimination of respiratory events and related arousals. During the CPAP titration, arousals related to respiratory events caused by a decrease of CPAP pressure because of air leaks in a mask, or spontaneous waking caused by fragmented sleep would occur, and then the jerks would reappear (Fig. 2). Periodic limb movement and PSM showed no association to his PSG data.
Fig. 1a.
A 60-s excerpt from a portion of an overnight polysomnogram (PSG): Myoclonic jerks occur during relaxed wakefulness. The electomyographic (EMG) bursts start in the right rectus abdominis (R Abd) and spread to the intercostal muscles (ICM).
Fig. 1b.
A 2-min excerpt from a portion of an overnight PSG: During sleep (stage1), myoclonic jerks resolved, and then jerks were noted following the termination of the obstructive hyponic event (OH) accompanied by arousal.
Fig. 1c.
A 2-min excerpt from a portion of a split night PSG with CPAP: During stable sleep (stage 2), jerks disappear, and then restarted after awakening.
Fig. 1d.
A 30-s excerpt from a portion of an overnight PSG: jerks started first in the rectus abdominis.
Fig. 2.
Hypnogram showing the relationship between myoclonic jerks (myoclonus), the sleep–wake cycle (stage), and arousals (arousal and awake). Without CPAP (in the first half), his sleep status is unstable because of obstructive apneic and hyponic events, and many myoclonic bursts occur. In the second half (with CPAP), respiratory events decrease and sleep status becomes stable, and the frequency of jerks decrease.
After the initiation of CPAP treatment, the frequency of jerks decreased and the patient never complained about jerks.
3. Discussion
PSM is one type of myoclonus that is proposed to originate from the spinal cord and spread up and down. PSM is a rare movement disorder characterized by myoclonic jerks consistently involving abdominal wall muscles, which worsen in the lying position and the wake–sleep transition phase [1]. Patients with isolated wake–sleep transition PSM are recognized as having a milder form of a single clinical and neurophysiologic entity [2]. The International classification of Sleep Disorders 2nd edition defined this entity as PSM at sleep onset [3]. Respiratory-related arousals are associated with increased motor activity [4]. It is reported that the jerks arise upon relaxed wakefulness and drowsiness and disappear upon mental activation and at sleep onset in PSM (2), but association with respiratory-related arousals has not been mentioned. The recurrence of jerks in our patient at the end of the respiratory events followed by arousals suggests that an arousal may trigger jerks in PSM at sleep onset in obstructive sleep apnea patients, and relative changes in the firing patterns of the neurons in the wake–sleep transition phase may be deeply connected to a release of a spinal generator responsible for PSM. It is not clear if triggering PSM depends solely on the arousal intensity (hierarchy), or if desaturation by respiratory events has an influence on triggering PSM. This is the first case suggesting that respiratory-related arousals provide a permissive window for PSM. Further studies are needed to clarify the pathophysiological associations between PSM and EEG arousal and cyclic alternating pattern.
Conflicts of Interest
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: doi:10.1016/j.sleep.2011.06.012.
Conflicts of Interest. ICMJE Form for Disclosure of Potential Conflicts of Interest form.
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PII: S1389-9457(11)00268-1
doi:10.1016/j.sleep.2011.06.012
© 2011 Elsevier B.V. All rights reserved.
