Facial nerve electroneurography. Variability in normal subjects

Assessment of Nerve Conduction in Patients With Lower Motor Neuron Facial Paralysis

Introduction Bell's palsy (BP), a lower motor neuron facial paralysis, commonly causes dysfunction of muscles of facial expression. Nerve conduction electrodiagnostic studies differentiate early-stage minor conduction blocks from later-stage Wallerian degeneration. Nerve conduction studies (NCSs) assess facial nerve function by delivering supramaximal electrical stimulus at the stylomastoid foramen. The amplitude loss percentage of the affected side is calculated with reference to the normal side. Aim The study's aim was to characterize the ncs in BP cases and to evaluate the correlation between the Compound Muscle Action Potential (CMAP) of the muscles affected. Materials and methods One hundred and four NCS data of BP cases were retrospectively collected over the period of two years. Statistical analyses of variables were done using the Chi-square test, one-way ANOVA, and Pearson correlation coefficient. Result The greater amplitude loss was seen in the orbicularis oris muscle innervated by buccal and mandibular branches of the facial nerve. The bivariate correlation between the Right Nasalis versus Right Orbicularis Oculi and Left Orbicularis Oculi versus Left Nasalis showed a highly significant moderately Strong Positive Correlation with an R-value of 0.687 and 0.558, respectively. The amplitude drop percentage was statistically significant in the affected left and right sides with P values of 0.008 and 0.007 respectively (P value < 0.05). The amplitude drop between the nasalis, orbicularis oculi and orbicularis oris muscles of both sides was statistically significant with a P value of 0.001. Conclusion NCS should be mandatorily included as an assessment protocol in BP cases for quantification of nerve degeneration and as a prognostic tool during the course of treatment.

The Offprint of an Abnormal Pre-Parotidectomy Electrodiagnostic Finding in a Normally Functioning Facial Nerve: Correlation with Intraoperative Findings, Histology and Postoperative Facial Nerve Function

The aim of this study was to search for associations between an electrodiagnostically abnormal but clinically normal facial nerve before parotidectomy and the intraoperative findings, as well as the postoperative facial nerve function. The records of all patients treated for parotid tumors between 2002 and 2021 with a preoperative House–Brackmann score of grade I but an abnormal electrophysiologic finding were studied retrospectively. A total of 285 patients were included in this study, and 222 patients had a benign lesion (77.9%), whereas 63 cases had a malignant tumor (22.1%). Electroneurographic facial nerve involvement was associated with nerve displacement in 185 cases (64.9%) and infiltration in 17 cases (6%). In 83 cases (29.1%), no tumor–nerve interface could be detected intraoperatively. An electroneurographic signal was absent despite supramaximal stimulation in 6/17 cases with nerve infiltration and in 17/268 cases without nerve infiltration (p < 0.001). The electrophysiologic involvement of a normal facial nerve is not pathognomonic for a malignancy (22%), but it presents a rather rare (~6%) sign of a “true” nerve infiltration and could also appear in tumors without any contact with the facial nerve (~29%). Of our cases, two thirds of those with an anatomic nerve preservation and facial palsy had already directly and postoperatively recovered to a major extent in the midterm.

Does Evoked Electromyography Detect the Injured Facial Nerve Recovery Earlier Than Clinical Assessments?

PURPOSE

The key element in managing postoperative facial nerve (FN) injuries is timely diagnosis and intervention as indicated. The purpose of this study was to measure and compare evoked electromyography (EEMG) and clinical assessment in terms of the recovery of the injured FN in operated temporomandibular joint ankylosis (TMJA) cases.

METHODS

The investigators designed a prospective cohort study in the primary operated TMJA patients. The primary predictor variable was the technique used to assess FN function, House-Brackmann Facial Nerve Grading System (HBFNGS) or EEMG. The primary outcome variable was time to FN recovery. The FN recovery was assessed in different time points (1 week, 1 month, 3 months, and 6 months). Age, gender, side (unilateral/bilateral), type of ankylosis (Sawhney's classification), and operating time were kept as covariates. Categorical variables were analyzed using Fisher's exact test. Multilevel survival analysis was performed considering the subject as cluster to perform Kaplan-Meier analysis and compute the hazards ratio using the Cox-regression method with adjustment for covariates. P <0.05 was set as statistically significant.

RESULTS

The study sample composed of 43 (69 sides) TMJA cases who underwent surgery developed iatrogenic FN injury in 10 cases (14 sides [9 right; 5 left]). The incidence of FN injury was 20.3% (14/69). Sawhey's type III/type IV ankylosis and the operating time for more than 2 hours showed a statistically significant (p<0.05) increase in FN injury. The mean duration to detect FN recovery by EEMG was 9 days (95% confidence interval, 5 to 12 days), but the HBFNGS took 161 days (95% confidence interval, 141 to 181 days). The chance of early detection by EEMG was 18.6 times more than the chance by the HBFNGS (Cox-hazard ratio, 18.6).

CONCLUSIONS

To conclude, EEMG is a noninvasive and reliable tool that detects FN recovery much earlier than the HBFNGS in the postoperative TMJA cases.

Facial electroneurography in Bell's palsy. Variability in the early stage and comparison between interpretation methods

To determine the variability of the abnormalities found in the electroneurography (ENG) of the facial nerve in cases of Bell's palsy during the initial two week period was one of the objectives of the authors. A second one was to investigate the value of ENG as a tool to determine an early prognosis of recovery utilizing two different methods. In the first one the amplitude of the compound muscular action potential (CMAP) obtained on the paralyzed side was compared to this potential on the opposite (normal) side. The second method compared the CMAP on the paralyzed side to normal standardized data from normal individuals. A group of 33 patients with Bell's palsy was followed until total recovery of for at least 4 months, if the recovery was not achieved earlier. It was observed that amplitude of the CMAP become stable towards the sixth day of palsy and this is a good time to establish the prognosis. Another conclusion is that both methods were equivalent to determine the prognosis in Bell's palsy.