Vagus nerve stimulation (VNS) is an established adjunctive treatment for individuals with drug-resistant epilepsy, particularly when surgical resection is not feasible. The procedure is generally considered safe and well-tolerated; however, complications can occur, including damage to the thoracic duct, peri-tracheal hematoma, surgical site infection, and symptoms related to traction on the recurrent laryngeal nerve, such as hoarseness, dyspnea, and dysphagia. A rare but notable complication is Horner syndrome, characterized by ipsilateral ptosis, miosis, and anhidrosis, resulting from disruption of the sympathetic pathway during cervical surgery. We report the case of a 16-year-old female with medically refractory epilepsy who developed clinical features of left-sided Horner syndrome immediately following VNS implantation.

A 16-year-old female with drug-resistant epilepsy and a history of developmental delay secondary to childhood lead poisoning underwent VNS implantation after failing multiple anti-seizure medications, including levetiracetam, brivaracetam, oxcarbazepine, and perampanel. Video electroencephalography monitoring confirmed multifocal seizure onsets, while brain magnetic resonance imaging revealed no structural abnormalities. The VNS procedure was performed without any reported intra-operative complications. However, immediately post-operatively, patient developed left-sided ptosis, miosis, and decreased sweating of the forehead, findings consistent with Horner syndrome. Neuroimaging ruled out any vascular injury or hematoma. Symptoms persisted at her 16-week follow-up, with no reported improvement and no additional postoperative complications.

Horner syndrome is a rare but important complication of VNS implantation. With very few cases documented in the literature, it remains uncommon, and clinicians should maintain a high index of suspicion when characteristic signs appear postoperatively. The condition is likely caused by unintentional traction or injury to the sympathetic pathway during surgical manipulation near the carotid sheath. Although no intraoperative complications were observed, the temporal relationship between the surgery and symptom onset supports a procedure-related etiology. Early recognition is essential for appropriate evaluation and monitoring of symptom progression or resolution.