Objective  To investigate the relationship between the thresholds of intraoperative facial nerve response and postoperative facial nerve function recovery in patients with Bell's palsy.

  Methods  Clinical data from Bell's palsy patients who underwent facial nerve decompression surgery at Beijing Tiantan Hospital from October 2015 to October 2022 were collected. The patients selected for analysis had intraoperative facial nerve monitoring with accurate recording of the facial nerve direct stimulation threshold and at least 1 year of detailed follow-up. The patients with postoperative facial nerve function recovery to grade Ⅰ-Ⅱ (HB grading) were defined as having good recovery, while those recovering to grade Ⅲ or higher were defined as having poor recovery. The patients were divided into two groups (A and B) according to facial nerve reaction excitability, with group A having a direct stimulation threshold of ≤1.5 mA and group B having a direct stimulation threshold of > 1.5 mA or a stimulation volume up to 3 mA without being able to record neural response waveform. The relationship between postoperative facial nerve function recovery and facial nerve direct stimulation threshold was analyzed.

  Results  A total of 36 Bell's palsy patients were included in this study, who underwent facial nerve decompression surgery through the transmastoid-epitympanum approach within 1-3 months after onset. Of the 36 patients, 24 (66.7%) had good recovery and 12 (33.3%) had poor recovery. Only 20 (55.6%, 20/36) patients had facial nerve direct stimulation threshold recorded during the operation, and all were ≤1.5 mA(0.1-1.5 mA). The reaction waveforms of 16 (44.4%, 16/36) patients could not be recorded even when facial nerve stimulation increased to 3 mA. There was no significant difference in age, gender, lateral discourse, timing of surgery, and preoperative electroneurography (ENoG) between the two groups(all P > 0.05), but the good recovery rate of the patients in group A was significantly higher than that in group B, and the difference was statistically significant (P=0.009).

  Conclusion  For patients with Bell's palsy undergoing decompression surgery of the facial nerve, the intraoperative direct stimulation threshold of the facial nerve may have some predictive value for postoperative facial nerve function recovery.