EMG vagus nerve stimulator artifact.

EMG artifact produced by a VNS stimulator is described. A patient with a VNS stimulator underwent an EMG study for suspected ALS. Artifacts that appeared similar to positive sharp waves or fibrillations were noted that could produce a false clinical diagnosis. These VNS-EMG artifacts matched well with the VNS generator's set parameters. We conclude that EMG findings must be interpreted with caution in patients with VNS implants and also that EMG may have a possible monitoring value for VNS activity.