Accelerometry May be Superior to EMG for Early Evaluation of Vocal Cord Function After Nerve Injury in a Pig Model

OBJECTIVE

Vocal cord (VC) movement has been demonstrated by the use of accelerometry (ACC) to decrease in parallel with the electromyographic amplitude (EMG) during ongoing traction injury to the recurrent laryngeal nerve (RLN). When RLN function recovers, discrepancies between EMG and VC movement have been reported in clinical and experimental studies. The present study was conducted to clarify the actual relationship between EMG and VC movement measured by ACC during nerve recovery.

METHODS

EMG obtained by continuous nerve monitoring (C-IONM) was compared with ACC during traction injury to the RLN, and throughout 40-min nerve recovery. A three-axis linear accelerometer probe was attached to the VC, and ACC data were registered as described. Traction damage was applied to the RLN until there was a 70% amplitude decrease from baseline EMG, or until loss of signal (LOS), that is, EMG values ≤100 μV.

RESULTS

Thirty-two RLN from 16 immature pigs were studied. Correlation between EMG and ACC were calculated during nerve injury and nerve recovery. The mean correlations were for the 70% and LOS group from start to end of traction: 0.82 (±0.17) and 0.87 (±0.17), respectively. Corresponding correlation coefficients during 40-min recovery was 0.50 (±0.48) in the 70% group and 0.53 (±0.33) in the LOS group.

CONCLUSION

There is a high correlation between EMG and VC movement during nerve injury, and a moderate correlation during early nerve recovery. EMG recovery after RLN injury ensures sufficient VC function as assessed by ACC.

LEVEL OF EVIDENCE

N/A Laryngoscope, 134:1485-1491, 2024.

Medullary Thyroid Carcinoma

Medullary thyroid carcinoma (MTC) is subdivided into sporadic (75%) and hereditary (25%) forms. Several germline mutations in the RET proto-oncogene are the source of distinct clinical phenotypes in hereditary MTC including familial MTC (FMTC) and multiple endocrine neoplasia 2A (MEN 2A) and 2B (MEN 2B). The higher the penetrance of the MEN 2 phenotype the earlier the progression of MTC which forms the basis for the currently recommended codon-related concept of prophylactic thyroidectomy. In patients with sporadic MTC, routine calcitonin (CT) measurement in nodular goiter patients has been shown to reduce the frequency of advanced tumor stages. Patients with CT levels over 100 pg/ml after pentagastrin stimulation are recommended for total thyroidectomy. In patients with unexpected sporadic MTC after histological examination, completion thyroidectomy is currently only recommended when CT levels remain elevated. The extent of lymph node dissection in patients with MTC is controversial. However, with respect to lymphonodal micrometastases, systematic compartment-oriented microdissection has been shown to reduce the frequency of lymphonodal recurrence. On the other hand, to avoid unnecessary lymph node dissection, a more individualized concept is required in the future. New chemotherapeutic agents (tyrosine kinase inhibitors), therapeutic nuclids (90Yttrium-labeled octreotide), and chemoembolization of liver metastases are currently the most promising therapeutical concepts in patients with distant metastases.

Calcitonin kinetics in the early postoperative period of medullary thyroid carcinoma

INTRODUCTION

Calcitonin is a sensitive marker for medullary thyroid carcinoma. Normalisation of calcitonin levels following resection of medullary thyroid carcinoma has been described after a few hours; however, it may be observed more than 4 weeks after surgery. The aim of this study was to correlate the postoperative calcitonin kinetics with preoperative calcitonin levels and tumour stage. Furthermore, we wanted to test the prognostic impact of the calcitonin kinetics. Therefore, only patients with postoperative normalisation of calcitonin levels (biochemical cure) were included in this study.

METHODS

Fourteen biochemically cured patients were analysed, including measurement of postoperative basal and pentagastrin-stimulated calcitonin concentration. With respect to the time of postoperative basal calcitonin normalisation, patients were classified into two groups: (A) patients with normalisation of basal calcitonin levels within 24 h and (B) patients with normalisation of basal calcitonin levels later than 24 h postoperatively.

RESULTS

Eight patients were found to have normalisation of basal calcitonin levels within 24 h (group A). In the remaining six patients (group B), the period to normalisation of basal calcitonin levels varied from 6 days to 14 days and longer. There were no differences between the two groups with regard to tumour size, number and pattern of lymph node metastases and tumour stage. However, preoperative basal calcitonin levels were significantly different (258 ng/ml vs 955 ng/ml, P<0.01). In the group with slow-decreasing calcitonin levels, no strong correlation between the preoperative level and the postoperative time to normalisation of basal calcitonin levels could be established, which may be due to the small number of patients. After a median follow-up of 21 months, no patient developed tumour recurrence. However, an increased basal calcitonin level was observed in one patient from group B. All other patients had normal basal and peak calcitonin levels.

CONCLUSION

Using a highly sensitive calcitonin assay, we demonstrated that normalisation of basal calcitonin levels may be delayed in patients suffering from medullary thyroid carcinoma. The lack of correlation of preoperative levels and the time to normalisation of the basal calcitonin levels, as well as the positive pentagastrin test in some of the patients, argues that this phenomenon is not simply due to prolonged biochemical calcitonin elimination. Nevertheless, a prognostic influence could not be shown in this study due to the short follow up-period. Further investigations and a longer follow-up are necessary to determine the nature and the prognostic impact of delayed normalisation of calcitonin levels.