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.