Teaching NeuroImages: Obstructive sleep apnea triggered by vagus nerve stimulation

A 47-year-old man with drug-resistant cryptogenic epilepsy, treated with vagus nerve stimulation (VNS), underwent polysomnography (PSG) for suspected obstructive sleep apnea (OSA). A previous PSG study, performed 1 year before VNS, had showed an apnea-hypopnea index (AHI) 5.4 events/hour, but the patient reported that the activation of the VNS was associated with increase of apneas witnessed by his bed partner. PSG was consistent with mild OSA; the AHI was 14.0 events/ hour. During PSG, the stimulator was active for periods of 30 seconds, generating a peculiar artifact (figure, black arrows), separated by a 3-minute interval. In 67% of the obstructive events (9.5 events/hour), the onset of the event was simultaneous or immediately followed the start of VNS activation,\r\nsuggesting that VNS might trigger obstructive apneas/hypopneas1,2 (figure, white arrows).