Recovery of Vocal Cord Function After Thyroid Surgery Often Takes Months with Loss of Signal During IONM as an Independent Predictor of Prolonged Recovery

Background: Post-thyroidectomy vocal cord dysfunction (PT-VCD) is an important side effect of thyroid surgery. With the introduction of IONM, hopes have been raised that either the rate or severity of PT-VCD could be reduced. However, data to support these concepts are scarce. To better understand the relationship between IONM outcomes and the severity of PT-VCD, a detailed time course evaluation of recovery of PT-VCD was performed in a continuous clinical quality registry from a specialized high-volume endocrine surgery center. Methods: Retrospective analysis of prospectively documented data from a clinical quality assurance registry from June 2015 to May 2016 with a 12-month follow-up of all cases. All patients underwent vocal cord (VC) laryngoscopy (VCL) by independent ENT specialists before and after surgery. Cases with newly diagnosed PT-VCD were enrolled in a detailed follow-up program (recruiting from June 2015 to May 2016) and structured telephone interviews every 4-6weeks to assess the exact time course of PT-VCD recovery and VC status for periods of at least 12 months. Clinical data were analyzed for variables affecting the time course of recovery by univariate analysis. Results: From 6/2015 - 5/2016 there were 1097 consecutive thyroid procedures. During this period, there were 78 PT-VCD (1591 nerves at risk (NAR); 4,9 %) entered into the detailed follow-up-program. Of these, 3 PT-VCD persisted at 12 months (PT-VCD 0,18 % NAR), with 6 LOF (maximum rate of potentially persisting PT-VCD of 0,54% NAR). 15% of PT-VCD recovered within 4 weeks, mean recovery time was 4.4 months and 6 months after thyroidectomy 18 % still had impaired VC laryngoscopy tests. Individual cases were followed > 12 months showing late full recovery of PT-VCD, challenging the definition of permanent VCD. Logistic regression analysis revealed non-transitory loss of signal (ntLOS) (OR for recovery within 12 weeks 0.39 (95%CI 0.15-0.98), p= 0.046) and more specific, secondary ntLOS to be a significant independent predictor of PT-VCP recovery > 12 weeks (OR for recovery within 12 weeks 0.303 (95%CI 0.115-0.797), p= 0.016). Conclusion: For the first time, these data provide a detailed description of the time course of PT-VCD recovery in a large cohort and a correlation with operative data and IONM. We found that recovery takes a long time and non-transitory loss of signal – especially secondary ntLOS - during IONM was associated with prolonged PT-VCD recovery. Therefore, IONM provides an additional benefit and early initiation of speech therapy may be advisable for these patients.