Facial nerve conduction study in the prognosis of bell’s palsy outcome by using fngs 2.0 – Le Trung Duc

Journal of military pharmaco-medicine no5-2018 188 FACIAL NERVE CONDUCTION STUDY IN THE PROGNOSIS OF BELL’S PALSY OUTCOME BY USING FNGS 2.0 Le Trung Duc*; Nguyen Duc Thuan*; Nguyen Tien Son* SUMMARY Objectives: To evaluate the prognosis value of facial nerve conduction study in Bell’s palsy outcome. Subjects and methods: A descriptive and cross-sectional study using electro diagnostic data and medical chart review on 29 patients diagnosed with Bell’s palsy in Department of Neurology, Military Hospital 103 from January 2017 to December 2017, were evaluated using the facial nerve grading system 2.0 (FNGS) during their initial visit and on day 20 and day 40. We performed facial nerve conduction studies (NCS) in the first 5 days and on the 20 th day. Facial NCS results were classified into amplitude loss less than 75% and amplitude loss 75% or greater to stratify into good or poor prognosis. Results: In the first 5 days, the amplitude loss was less than 75% in 13 patients (44.8%) and 75% or greater in 16 patients (55.2%). On the 20 th day, the amplitude loss was less than 75% in 8 patients (27.6%) and 75% or greater in 21 patients (72.4%). There was a statistically significant correlation between patients with compound muscle action potential (CMAP) amplitude difference 75% or higher in the first 5 days and those with FNGS 2.0 equal to grade 3 or above (Chi Square = 9.311, p = 0.004). There was a statistically significant correlation between patients with CMAP amplitude difference 75% or higher on 20 th day and those with FNGS 2.0 equal to grade 3 or above (Chi square = 19.859, p < 0.001). Conclusion: The facial nerve conduction study is a valuable tool for follow-up and recovery prognosis of the Bell’palsy, especially in the subacute phase. Based on our data, poor prognosis is predicted in patients with more than 75% amplitude loss at both the initial and the follow-up facial NCS. * Key words: Bell’s palsy; Facial nerve; Nerve conduction study. INTRODUCTION Bell’s palsy, defined as an acute unilateral peripheral facial nerve palsy without detectable cause, is the most common cause of facial nerve palsy. FNGS 2.0, first introduced in 2009, was designed to overcome the limitations of existing grading systems like House Brackmann, Sunnybrook. Electrophysiological methods have been used to determine the severity of nerve degeneration and prognosis in IPFP since the 1960s. Currently, the nerve excitability test, NCS, blink reflex test and needle electromyography are used to determine the prognosis. The purpose of our study was: To evaluate the prognosis value of facial nerve conduction study in Bell’s palsy outcome by using FNGS 2.0. * Corresponding author: Nguyen Duc Thuan (thuanneuro82@gmail.com) Date received: 29/03/2018 Date accepted: 21/03/2018 Journal of military pharmaco-medicine no5-2018 189 SUBJECTS AND METHODS This is a prospective study on the patients with Bell’s palsy between the period of January 2017 to December 2017 in Neurology Department of Military Hospital 103. The study included 29 patients diagnosed with idiopathic peripheral facial paresis. Patients who were characterized by acute onset, isolated, unilateral, peripheral facial nerve paralysis without detectable cause were included. The clinical diagnosis of idiopathic peripheral facial paresis was based on the ICD-X criteria. Exclusion criteria were previous history of peripheral or central facial paralysis, diabetes and other peripheral neuropathies. All patients were treated with methylprednisolon 80 mg/day IV within 7 days and neurotrophic drugs after the onset of disease. The initial dose of methylprednisolon was administered for a week and then tapered gradually over the following week. Clinical evaluation comprised the FNGS and facial NCS was conducted in the first 5 days and 20th and 40th days after paralysis onset. We defined a good outcome as the FNGS grade I or grade II and a poor outcome as FNGS grade 3 or higher. Table 1: FNGS 2.0 Score Brow Eye NLF Oral Degree of secondary movement 1 Normal Normal Normal Normal None 2 Slight weakness > 75% of normal Slight weakness > 75% of normal Complete closure with mild effort Slight weakness > 75% of normal Slight weakness > 75% of normal Slight synkinesis, minimal contracture 3 Obvious weakness > 50% of normal Resting symmetry Slight weakness > 75% of normal Complete closure with maximal effort Slight weakness > 75% of normal Resting symmetry Slight weakness > 75% of normal Resting symmetry Obvious synkinesis, mild to moderate contracture 4 Asymmetry at rest < 50% of normal Cannot close completely Asymmetry at rest < 50% of normal Asymmetry at rest < 50% of normal Asymmetry at rest < 50% of normal Disfiguring synkinesis, severe contracture 5 Trace movement Trace movement Trace movement Trace movement 6 No movement No movement No movement No movement Journal of military pharmaco-medicine no5-2018 190 Grade Total score I 4 II 5 - 9 III 10 - 14 IV 15 - 19 V 20 - 23 VI 24 * Electrophysiological assessment: All patients underwent facial NCS on admission using Natus VikingQuest. Facial NCS was performed first on the intact side and then repeated on the affected side. Potentials were recorded from each of the frontal, orbicularis oris and orbicularis oculi muscles. The stimulation intensity ranged from 30 to 45 mA. The current intensity was increased stepwise until there was no further incrase in the amplitude of the diphasic myogenic CAP. An additional 10% of current was added to ensure supramaximal stimulation. The amplitude of the CMAP in the affected side and the intact side were compared. The value of 75% or less versus more than 75% amplitude loss was considered a cut-off point for prognosis. *Statistical analysis: Statistical analysis of the data was performed using Statistical Package for Social Sciences software package. Sensitivity, specificity, positive predictive value and negative predictive value were caculated to determine the prognostic value of facial NCS. The Mann-Whitney test was used to compare the facial NCS result with clinical improvement. The Mc Nemar test was used to compare the performances of facial NCS in the first 5 days with those on the 20th day. The significance level was set at p < 0.05. RESULTS 1. Clinical evaluation. Twenty nine patients (19 males and 10 females; mean age 44.3 years, range: 20 - 79 years) diagnosed with Bell’s palsy were studied. In the first 5 days, the clinical evaluation according to the FNGS revealed that 4 patients (13.8%) was in grade III, 6 patients (20.7%) in grade IV, 18 (62%) in grade V and 1 patien (3.5%) in grade VI. On the 40th day, the final outcome based on FNGS was grade I in 17 patients (58.6%), grade II in 6 patients (20.7%) and grade III in 6 patients (20.7%). 12 out of 19 patients (63.1%) with complete facial nerve paralysis returned to normal function. All patients with incomplete lesions had normal facial nerve function in the 40th day. 2. NCS. On the first 5 days, the amplitude loss was less than 75% in 13 patients (44.8%) and 75% or greater in 16 patients (55,2%). On the 20th day, the amplitude loss was less than 75% in 8 patients (27.6%) and 75% or greater in 21 patients (72.4%). Journal of military pharmaco-medicine no5-2018 191 21 2 0 6 0 5 10 15 20 25 Amplitude difference = 75% FNGS 2.0 grade I, II FNGS 2.0 grade 3 or higher Figure 1: Relationship between FNGS 2.0 grade on the day 40 and CMAP amplitude difference on the day 20. Sensitivity, specificity, PPV and NPV of NCS results are presented in table I. Poor prognosis was defined as a positive test result, good prognosis was defined as a negative test result. For initial NCS, we found a PPV and NPV of 46% and 93.8%, respectively. After a period of 15 days, PPV and NPV of follow-up NCS increased to 75% and 95.2%. Table 2: Predictive value of facial NCS. There was a statistically significant relationship between patients with CMAP amplitude difference 75% or higher in the first 5 days and those with FNGS 2.0 equal to grade 3 or above (Chi square = 9.311, p = 0.004). There was a statistically significant relationship between patients with CMAP amplitude difference 75% or higher on 20th day and those with FNGS 2.0 equal to grade 3 or above (Chi square = 19.859, p < 0.001). Mc Nemar's test was used in order to compare NCS in the first 5 days and NCS on 20th day. NCS on the 20th day show the best performance (p < 0.05). DISCUSSION For patients with Bell’s palsy in the acute phase, the NCS showed reduced amplitudes of CMAP in the frontal, orbicularis oculi muscle and orbicularis oris muscle on the affected side and the normal amplitudes on the intact side. Statistically, the disease course was described in a study by Peitersen E [3] on 1.011 patients. One-third had an incomplete paralysis, two-thirds had complete paralysis. Sensitivity Specificity PPV NPV NCS on the first 5 day 85.7 % 68.2% 46.2% 93.8% NCS on the day 20 85.7 % 90.9% 75% 95.2% Journal of military pharmaco-medicine no5-2018 192 94% of the patients with incomplete lesions returned to normal function, while only 60% of those with clinically complete lesions returned to normal function. Among 19 patients with complete facial nerve paralysis in the present study, 12 patients (63.1%) returned to normal function. All of patients with incomplete lesions had normal facial nerve function on the 40th day, which reveals that we had a representative population, according to previous studies. Jabor et al reported that prognosis is favorable if some recovery is seen within the first 21 days of onset [4]. In our study, we performed facial NCS in the first 5 days and on the 20th day. There was a statistically significant relation between patients with CMAP amplitude difference 75% or higher both in the first 5 days and on day 20 and patients with poor recovery on the 40th day after onset. However, NCS results on day 20 illustrate a higher prognosis value than those in the first 5 days (McNemar test, p < 0.05), which is probably consistent with axonal recovery and collateral sprouting process of facial nerve. Our results are consistent with those that reported CMAP amplitude differences of ≥ 75% indicate a poor prognosis at 3 months [7]. Ozgul et al investigated the disease 3 months after the onset, which indicates similar findings. Besides, some studies reported 50% and 90% CMAP amplitude difference in the second month and in the third week respectively, which indicated poor prognosis unlike other studies [1, 2]. In our study, we utilize FNGS 2.0. Few studies have compared FNGS 2.0 and House Brackmann grading systems and confirmed whether FNGS could evaluate facial nerve function more detail and accuracy than House Beckmann scale [5, 6]. CONCLUSION The facial NCS is a valuable tool for follow-up and recovery prognosis of the Bell’palsy, especially in the subacute phase. Based on our data, poor prognosis is predicted in patients with more than 75% amplitude loss at both the initial and the follow-up facial NCS. REFERRENCES 1. Fisch U. Surgery for Bell’s palsy. Arch Otolaryngol. 1981, 107, pp.1-11. 2. Danielides V, Skevas A, Van Cauwenberge P. A comparison of electroneuronography with facial nerve latency testing for prognostic accuracy in patients with Bell’s palsy. Eur Arch Otorhinolaryngol. 1996, 253 (1-2), pp.35-38. 3. Peitersen E. The natural history of Bell's palsy. Am J Otol. 1982, 4, p107. 4. Jabor M.A, Gianoli G. Management of Bell's palsy. J La State Med Soc. 1996, 148, p.279. 5. Ho Y. Lee, Moon S. Park. 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