From the Department of Pulmonary, Critical Care and Sleep Disorders Medicine (Dr El-Kersh), and Department of Pediatrics, Division of Sleep Medicine (Dr Senthilvel), University of Louisville, Louisville, KY.
CORRESPONDENCE TO: Karim El-Kersh, MD, Department of Pulmonary, Critical Care and Sleep Disorders Medicine, Ambulatory Care Bldg, 550 S Jackson St, Louisville, KY 40202; e-mail: email@example.com
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An 18-year-old woman with a history of refractory complex partial epilepsy presented for evaluation of snoring and episodes of gasping for air during sleep. She had uncontrolled epilepsy since the age of 8 years despite trial of multiple antiepileptic medications. She eventually underwent an implantation of a vagus nerve stimulator (VNS) device (model 103; Cyberonics Inc) with gradual adjustment of the VNS settings for better seizure control.
The patient was afebrile with stable vital signs. Her BP was 130/70 mm Hg, heart rate was 95 beats/min, height was 169 cm, and weight was 101 kg with a calculated BMI of 35. General physical examination findings were within normal limits. Head and neck examination revealed normal palate and Mallampati class 4, grade 1 tonsils with no maxillary retrusion.
The patient underwent a diagnostic overnight polysomnography that showed snoring and an overall apnea-hypopnea index of 8.6 events/h of sleep (obstructive hypopnea index, 8.2; obstructive apnea index, 0.2). Several episodes of airflow limitations without arousals or desaturations were noted, but they did not qualify to be scored as events. Both the scored and unscored events were cyclic and associated with raised submental electromyographic tone (Fig 1).
OSA and epilepsy frequently coexist. It is estimated that the prevalence of OSA in drug-resistant epilepsy can be up to 30%.
Vagus nerve stimulation is used as an adjunctive therapy for epilepsy refractory to medical treatment. The device generator is implanted subcutaneously and is connected to the vagal electrodes via tunneled leads that usually reach the left vagus nerve. The device settings can be incrementally adjusted to achieve better seizure control. The exact mechanism of seizure control is unknown but it can be related to an increase in the thalamic blood flow, desynchronization of cortical EEG, and alterations in central chemical neurotransmitters such as gamma-aminobutyric acid, among others.
During sleep, vagus nerve stimulation can result in reduction of respiratory effort and tidal volume and an increase in respiratory rate during periods of stimulation. Furthermore, vagus nerve stimulation can result in upper airway narrowing and obstruction, due to stimulation of upper airway musculature supplied by the vagus nerve. These mechanisms can result in an increase in the obstructive apnea-hypopnea index in patients treated with the vagus nerve stimulator (VNS). Besides the obstructive events, vagus nerve stimulation can rarely be associated with central sleep apnea as well. The precise mechanism of central events remains to be elucidated. Interestingly, the reduction of vagal tone was the proposed mechanism of reduced obstructive and central apnea events in patients with sinus node dysfunction and sleep apnea who underwent atrial overdrive pacing. Due to the limited number of studies, the prevalence of OSA secondary to vagus nerve stimulation is not known, and it is difficult to predict who will develop clinically significant OSA after VNS implantation.
The interaction between OSA and epilepsy is complex. Furthermore, several medications used in treatment of epilepsy can promote weight gain, thus increasing the risk for OSA. Although treating OSA can help with seizure control, the effect of vagus nerve stimulation-induced sleep apnea on seizure control in patients with a VNS is not clear and needs further study.
Managing OSA in the setting of an implanted VNS can be challenging, and the treatment should be individualized. The treatment plan requires input from the patient, neurologist, and the sleep specialist to balance the control of both OSA and seizures. It is important to determine if the patient has an underlying OSA independent of the VNS. A cycling pattern of the events coinciding with the VNS cycling time points to the VNS as the plausible cause. If in doubt, or in cases with possible underlying OSA exacerbated by VNS placement, temporary magnet deactivation of the VNS can be attempted during a portion of the diagnostic study after consulting with the neurologist.
Therapeutic intervention should take into consideration both the severity of OSA and the degree of seizure control. Changing the VNS parameters via prolonging the cycling time and decreasing the stimulation frequency can assist OSA treatment. Close attention should be given to seizure control when attempting such changes, to find out the best tolerated settings.
If the VNS setting changes fail to control OSA or if they jeopardize seizure control, positive airway pressure therapy can be considered. In severe OSA cases not responding to VNS setting changes and/or positive airway pressure therapy, nocturnal magnet VNS deactivation or VNS discontinuation can be considered as the last options.
In this patient, the respiratory cyclic events were corresponding to the VNS on/off cycling time and were associated with raised submental electromyography tone (Fig 1). The OSA was suspected to be related to the cyclic VNS activation. The patient’s mother reported that she started noticing the snoring and gasping events after the last setting adjustment of the VNS (current: 1.25 mA; frequency: 20 Hz; pulse width: 250 μs; cycle: 7 s on/30 s off). The patient underwent VNS setting changes with reduction of both the output current and cycling time (current: 0.75 mA; frequency: 20 Hz; pulse width: 250 μs; cycle: 14 s on/300 s off). The mother noted improvement of the nocturnal gasping episodes, and the repeated polysomnography, which was performed 1 month after the first study and 16 days after VNS setting adjustment, showed an overall apnea-hypopnea index of 2 events/h of sleep (obstructive hypopnea index, 2).The several airflow limitations that were noted on the first study resolved (Fig 2).
1. There is a significant association between refractory epilepsy and OSA.
2. Vagus nerve stimulation therapy can cause sleep apnea or exacerbate an underlying sleep apnea.
3. Screen for symptoms of sleep apnea before and after VNS implantation.
4. Treatment of OSA in the setting of a VNS includes changing the VNS settings, positive airway pressure therapy, nocturnal VNS magnet deactivation, or VNS discontinuation.
Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
Other contributions: CHEST worked with the authors to ensure that the Journal policies on patient consent to report information were met.
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