Vagus Nerve Stimulation in a Case of Epilepsy with CSWSS: Respiratory Side Effects during Sleep

We would like to alert the medical community to pos-sible respiratory side effects of vagal nerve stimulation(VNS) during the treatment of nonsurgical refractorypartial epilepsy. We observed hypopneic–polypneic epi-sodes during sleep in a 9-year-old girl with epilepsy withcontinuous spike–waves during slow sleep (CSWSS)syndrome. These events were time-locked to each periodof VNS stimulation and occurred without any modifica-tion of cardiac frequency. VNS may elicit a reduction of25–50% in seizure frequency in both adults and childrenwith intractable epilepsy (1). Adverse side effects andcomplications of VNS were few and mostly transient andwere reported in adult patients only. They includehoarseness, neck pain, hypersalivation, cough, and short-ness of breath (“air-missing”) sensations during physicalexercise. These sensations might be related to the in-crease in end-expiratory volume observed in some pa-tients receiving stimulation at high intensity. In contrastto the common observation that VNS modifies the respi-ratory pattern in animals, only one study has reportedalterations in the respiratory pattern in humans (2).In the present case, the mother’s pregnancy wasmarked by fetal death of a twin sister at 24 weeks ofpostconceptional age. Birth was uneventful at 36 weeksof gestational age. Systematic transfontanellar ultrasoundanalysis revealed bilateral diffuse periventricular leuko-malacia. At age 2 years, she had right tonic partial sei-zures with loss of contact, and magnetic resonanceimaging (MRI) evidenced a left parietal extended isch-emic lesion.At age 5 years, her seizures changed and increased infrequency: during daytime, they were characterized byabsence seizures associated with mild and inconstant ato-nia (up to one seizure every 2–3 min). Sleep EEGshowed CSWSS. Over the course of the following year,she was treated unsuccessfully with seven different an-tiepileptic drugs (AEDs). A ketogenic diet also was in-effective. She was considered an ineligible candidate forsurgery because of the extent of the left sylvian ischemiclesion.At age 6 years, a neurocybernetic prosthesis (Cyberon-ics, Houston, Texas U.S.A.) was implanted. The stimu-lation allowed a drug-free period of 2 months, duringwhich there was an initial seizure-free period of 6 weeks.Then absences reappeared but were less numerous thanbefore implantation. Subsequently she was given la-motrigine (LTG) with VNS. Despite the use of variousAED combinations and changes in stimulation param-eters over the next year, the absences persisted.At age 6