Abnormal electromyographical trigeminal activation through stimulation of the offending artery (Z-L response): An intraoperative tool during microvascular decompression for trigeminal neuralgia

Background: There are currently no intraoperative neurophysiological tools to assess the effectiveness of trigeminal nerve decompression during microvascular decompression surgery for drug-resistant trigeminal neuralgia. In microvascular decompression surgery for hemifacial spasm, an abnormal electromyographic activation of facial muscles after stimulation of the offending vessel was identified and named ‘Z-L response’. Methods: We adapted a neurophysiological protocol to elicit a Z-L response during microvascular decompression surgery for trigeminal neuralgia and applied it to a prospective series of 18 surgical patients. Results: Patients had suffered from trigeminal neuralgia for a median 9-year timeframe, and median preoperative Barrow Neurological Institute pain score was 4.5. Through monopolar stimulation, using rising amplitudes starting from 0.1 mA, we confirmed intraoperatively the true culprit vessel before decompression. In 4/18 cases, multiple offending vessels were identified (22 conflicts overall). After decompression, a significant increase in activation threshold (p < 0.0001) confirmed the effectiveness of the maneuver; in 10 cases, Z-L response was abolished. Using this technique, we obtained excellent or good outcome (Barrow Neurological Institute 1–3) in all patients, with a significant reduction in postoperative Barrow Neurological Institute score as compared with preoperative one (median Barrow Neurological Institute 1; p = 0.0002). Conclusion: we provide the first evidence on the applicability and clinical usefulness of Z-L response during microvascular decompression surgery for trigeminal neuralgia.