VNS – Mechanism and Efficacy — SCE Neurology MCQ
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Correct answer: D — VNS delivers intermittent electrical stimulation to the left vagus nerve, which modulates brainstem nuclei (nucleus tractus solitarius, locus coeruleus) and diffusely alters cortical excitability — approximately 50% of patients achieve a ≥50% seizure reduction
VNS involves a pulse generator implanted subcutaneously in the left chest wall, connected to an electrode wrapped around the left vagus nerve in the neck. It delivers intermittent electrical stimulation that modulates ascending brainstem projections to the cortex (via NTS, locus coeruleus, raphe nuclei), reducing cortical excitability. Approximately 30–40% achieve ≥50% seizure reduction at 1 year, improving to ~50% by 2–3 years (efficacy increases over time). It does not typically render patients seizure-free but reduces seizure burden. The left vagus nerve is used because the right has more cardiac innervation. A: VNS modulates excitability rather than directly blocking seizures. C: Seizure freedom is uncommon. D: Proven efficacy in RCTs. E: Left vagus nerve is used.
Reference: NICE IPG50 VNS for Epilepsy; NICE NG217