Evaluation of Factors Associated With Favorable Outcomes in Adults With Bell Palsy

This cohort study examines the factors that are associated with the favorable outcomes, defined as a House-Brackmann grade of II or lower, in patients treated for Bell palsy.

Key Points

Question

Which factors are associated with improved outcomes in patients with Bell palsy?

Findings

In this cohort study of 1364 patients diagnosed with Bell palsy between 2005 and 2017, factors that were associated with improved facial function included younger age, a lower degree of initial facial nerve paralysis as measured using the House-Brackmann grade, good electromyography result (absence of pathological spontaneous fibrillation activity), absence of diabetes, and control of hypertension.

Meaning

The findings of this study suggest that multiple clinical factors may be associated with a favorable outcome in patients with Bell palsy.

Abstract

Importance

Identification of the factors associated with improved facial nerve function after treatment of Bell palsy is important to provide patients with early and effective treatment.

Objective

To identify factors that are associated with improved treatment outcomes in patients with Bell palsy.

Design, Setting, and Participants

This retrospective cohort study included 1364 patients with Bell palsy treated at the outpatient clinic of the Department of Otolaryngology at the Kyung Hee University Hospital, Seoul, Republic of Korea, between January 1, 2005, and December 31, 2017. The medical records of patients admitted to this hospital for management of acute facial palsy were reviewed by 3 otolaryngologists with more than 20 years’ experience in treating facial palsy.

Main Outcomes and Measures

Facial function at the initial and final visits were measured using the House-Brackmann (H-B) grading system, which is one of several analysis tools developed to quantify facial function and provide reproducible information. It is a widely accepted system for grading facial function in 6 steps, from normal (H-B grade I) to total paralysis (H-B grade VI).

Results

In total, 1364 patients with primary Bell palsy (718 [52.6%] women) and a mean (SD) age of 47.7 (16.7) years were enrolled. The overall rate of favorable outcome, which was defined as an H-B grade of I or II at the 6-month follow-up visit, was 80.6% (1099 of 1364 patients). Of 1099 patients who had a favorable outcome at 6 months, 343 (31.2%) were younger than 40 years. Of 1364 patients, 1053 (77.2%) had moderate facial dysfunction (H-B grade III or IV). No pathological spontaneous fibrillation activity (ie, good electromyography [EMG] results) was detected on EMG in 937 of 1364 patients (68.7%), 492 (36.1%) had controlled hypertension, and 673 (49.3%) were treated with oral corticosteroids alone. Multivariable analysis revealed that the following factors were associated with favorable outcome: age younger than 40 years (odds ratio [OR], 1.56; 95% CI, 1.09-2.22), an initial H-B grade of III or IV (OR, 2.62; 95% CI, 1.93-3.57), good EMG results after 2 weeks of treatment (OR, 3.38; 95% CI, 2.48-4.61), absence of diabetes (OR, 1.43; 95% CI, 1.04-2.36), and control of hypertension (OR, 1.64; 95% CI, 1.16-2.33).

Conclusions and Relevance

Multiple logistic regression analysis in this study suggests that multiple clinical factors are associated with favorable outcomes in patients with Bell palsy.

Introduction

Bell palsy is an idiopathic, acute palsy of the peripheral facial nerve supplying all muscles of the face.¹ It is a rapidly developing unilateral facial weakness with an unknown cause. The condition results in a partial or complete inability to spontaneously move the facial muscles on the affected side.² Bell palsy is clinically easy to diagnose, does not affect a patient’s mortality and life expectancy, and usually has a good prognosis. However, patients experience mental stress until the condition resolves, which may take some time if sequelae develop. The exact pathogenic mechanism is not well known, and treatment methods for complete resolution of symptoms have not yet been established. Recent studies have demonstrated that the major cause of Bell palsy is the reactivation of the latent herpes simplex virus type 1 or varicella zoster virus within the geniculate ganglia.³ The pathogenesis by which these viruses can cause neuropathy may begin with a cytotoxic edema induced by neuronal inflammation.⁴ These hypotheses have justified the use of corticosteroids and antiviral agents, separately or together, in the treatment of Bell palsy.

The incidence of Bell palsy is 20 to 30 cases per 100 000 people per year, accounting for 60% to 75% of all unilateral facial paralyses.^3,5 Men and women are equally affected and the disease can occur at any age.⁶ The facial weakness usually occurs within a maximum of 48 hours; it can be complete or partial and is generally unilateral.⁷ Although most patients with Bell palsy completely recover, up to 30% of the patients develop long-term sequelae, such as a permanent facial paresis, synkinesis, contracture, and facial asymmetry, even with appropriate treatment.^8,9 Therefore, the resolution of Bell palsy and risk of paralysis are of great concern to patients.

Previous studies^10,11,12 reported on several factors associated with prognosis based on a clinical evaluation of accompanying symptoms, underlying medical diseases (hypertension and diabetes), age, and the degree of degeneration of the facial nerve as determined using an electrophysiological test. Moreover, numerous studies^13,14 have been conducted on the epidemiology, cause, diagnosis, treatment, and prognosis of Bell palsy with the goal of providing early and appropriate treatment to achieve optimal outcomes. Current knowledge on the prognosis of Bell palsy remains limited owing to partial research of clinical factors, small study samples, and high possibility of bias in multicenter studies. In addition, no clear guidelines have been established for treating Bell palsy with the combination of corticosteroids and antiviral agents. Based on this background, we analyzed variables potentially associated with the outcome of Bell palsy. This study aimed to evaluate the outcomes of patients with Bell palsy and diagnostically classify specific factors that contribute to a favorable or unfavorable outcomes.

Methods

Study Design and Participants

This retrospective cohort study included patients who were diagnosed with acute facial palsy and were admitted to the Department of Otorhinolaryngology—Head and Neck Surgery at the Kyung Hee University Hospital, Seoul, Republic of Korea, from January 1, 2005, to December 31, 2017. The medical records of 1756 patients admitted to the hospital were reviewed by 3 of us (J.Y.B., S.H.K., and S.G.Y.) who have more than 20 years’ experience in treating facial palsy. Of 1756 patients, 392 patients were excluded based on the following exclusion criteria: central nervous system disorders, polyneuropathy such as Guillain-Barré syndrome, recurrent Bell palsy, iatrogenic facial nerve palsy, neoplasms, Ramsay Hunt syndrome, otitis media, pregnancy, herpes zoster oticus, bilateral facial palsy, unclear timing of onset, follow-up for less than 6 months, and House-Brackmann (H-B) grade II at admission. A total of 1364 patients were included in this study (Figure). This retrospective study was approved by the institutional review board of Kyung Hee University Hospital, Seoul, Republic of Korea. The requirement for written informed consent was waived by the Kyung Hee University Hospital owing to the retrospective nature of the study.

Figure. Flow Diagram of the Study Design.

Patients’ baseline characteristics were assessed before initiating treatment, including the findings of the otorhinolaryngological examination, grading of facial function, age, sex, and previous history of facial palsy. All patients were admitted to the hospital for at least 7 days. In addition, all patients were prescribed an ophthalmic ointment to prevent eye damage according to the American Academy of Otolaryngology guideline.² Except 61 patients who refused a corticosteroid treatment and underwent a conservative treatment instead, such as acupuncture or physical therapy, all other patients began treatment with an oral corticosteroid or a corticosteroid combined with an antiviral drug within 7 days from the onset of paralysis. The corticosteroid treatment consisted of oral prednisolone for 10 days, at a dosage of 1 mg/kg per day (maximum, 80 mg/d) for the first 4 days followed by tapering to 60 mg/d on days 5 and 6, 40 mg/d on days 7 and 8, and 20 mg/d on days 9 and 10. The antiviral treatment consisted of oral acyclovir, 1000-2400 mg/d, for 5 days or famciclovir, 750 mg/d, for 7 days. Physical therapy consisted of facial massage, facial expression practice, and treatment with an electrical stimulator.

Assessment of Outcome and Follow-up

The facial function was assessed using the H-B grading system.¹⁵ The following factors were recorded: patient’s sex and age, the degree of initial facial nerve paralysis represented by the initial H-B grade, the presence of underlying diseases, such as diabetes and hypertension, electrophysiological test results, and the degree of the final facial function. Three otolaryngologists (J.Y.B., S.H.K., and S.G.Y.) assessed the initial severity of Bell palsy using the H-B grading system. The degree of the initial facial palsy was classified as mild (H-B grade II), moderate (H-B grades III-IV), or severe (H-B grade ≥V). The degree of functional improvement was also assessed based on the H-B grade at every follow-up visit (14 days, 1 month, 3 months, and 6 months). At the 6-month follow-up visit, we reevaluated the H-B grade in all patients and defined favorable outcome as an H-B grade of I or II and an H-B grade III or higher as an unfavorable outcome.

Electroneurography (ENoG) and electromyography (EMG) were used for electrophysiological assessment. Electroneurography was performed on day 4 or 5 after the symptom onset, whereas needle EMG was conducted in all patients 2 weeks after the onset of facial palsy. Electroneurography measurements were reported as the percentage maximal amplitude on the affected side divided by the maximal amplitude on the normal side. A poor ENoG result was defined as a loss of amplitude greater than 90%, whereas loss of 90% or less was classified as a good outcome.¹⁶ In addition, the presence or absence of the blink reflex and the needle EMG findings were analyzed simultaneously to be classified as a poor or good outcome by the physical medicine and rehabilitation physician. The absence of pathological spontaneous fibrillation activity was defined as a good outcome, whereas the presence of abnormal spontaneous activity or absence of volitional activity was classified as a poor outcome.

Statistical Analysis

Clinical data are presented as mean (SD), with effect size presented as the difference in rates of favorable outcome and 95% CI around the difference. To evaluate the association between baseline variables, treatment, and outcome of Bell palsy, multivariable logistic regression analyses were performed and associations were reported as odds ratios (ORs) with 95% CIs.

Results

After excluding 392 patients who did not meet the inclusion criteria, 1364 patients with primary Bell palsy were enrolled (646 men [47.4%] and 718 women [52.6%]) (Table 1). The mean (SD) patient age was 47.7 (16.7) years. Of the 1364 patients registered, 1053 (77.2%) had an initial H-B grade of III or IV, 1279 (94.0%) had ENoG of 10% or greater, 937 (68.7%) had good EMG results, 179 (13.1%) had diabetes, 492 (36.1%) had controlled hypertension, 673 (49.3%) were treated with corticosteroids alone, 668 (49.0%) were treated with a combination of corticosteroid and an antiviral agent, and 23 (1.7%) were treated with supportive care alone. The overall rate of favorable outcome was 80.6% (1099 of 1364 patients). Among 1099 patients who had a favorable outcome, 343 (31.2%) were younger than 40 years. In addition, the initial H-B grade was III or IV in 885 of 1099 patients (80.5%), 412 (37.5%) had controlled hypertension, and 571 (52.0%) were treated with corticosteroids alone.

Table 1. Demographic, Clinical, Electrophysiological, and Treatment Variables Associated With Favorable Outcomes in Patients With Bell Palsy^a.

Variable	All Patients, No. (%) (N = 1364)	Favorable Outcome, No. (%) (n = 1099)	Effect Size Difference (95% CI), %
Sex
Male	646 (47.4)	523 (47.6)	0.74 (−3.46 to 4.94)
Female	718 (52.6)	576 (52.4)
Age, y
<40	407 (29.8)	343 (31.2)	5.28 (0.90 to 9.66)
≥40	957 (70.2)	756 (68.8)
Initial H-B grade
III-IV	1053 (77.2)	885 (80.5)	15.24 (9.63 to 20.84)
V-VI	311 (22.8)	214 (19.5)
Electroneurography results
≥10% (Good)	1279 (94.0)	1034 (94.1)	4.37 (−4.9 to 13.65)
<10% (Poor)	85 (6.0)	65 (5.9)
Electromyography resultsb
Good	937 (68.7)	818 (74.4)	21.49 (16.51 to 26.47)
Poor	427 (31.3)	281 (25.6)
Controlled hypertension
Yes	492 (36.1)	412 (37.5)	4.96 (0.71 to 9.20)
No	872 (63.9)	687 (62.5)
Diabetes
No	1185 (86.9)	964 (87.7)	5.93 (−0.75 to 12.62)
Yes	179 (13.1)	135 (12.3)
Treatment method
Oral corticosteroids alone	673 (49.3)	571 (52.0)	15.28 (1.48 to 34.86)
Combination antiviral therapy	668 (49.0)	512 (46.6)
Supportive care alone	23 (1.7)	16 (1.4)

Abbreviation: H-B grade, House-Brackmann grade.

^aFavorable outcome was defined as an H-B grade of II or lower.

^bGood results were defined as the absence of pathological spontaneous fibrillation activity.

Multivariable logistic regression analysis was performed to identify independent factors associated with the final outcome (Table 2). Favorable outcome (ie, H-B grade ≥III) was associated with age younger than 40 years (OR, 1.56; 95% CI, 1.09-2.22), lower initial H-B grade (OR, 2.62; 95% CI, 1.93-3.57), good EMG outcome after 2 weeks of treatment (OR, 3.38; 95% CI, 2.48-4.61), absence of diabetes (OR, 1.43; 95% CI, 1.04-2.36), and the control of hypertension (OR, 1.64; 95% CI, 1.16-2.33). Moreover, after controlling for important demographic characteristics and baseline clinical factors (age, sex, initial H-B grade, underlying disease such as hypertension and diabetes, and electrophysiological test findings), treatment with an oral corticosteroid alone did not show any statistically significant independent difference in the OR compared with combination antiviral therapy. Results of the multivariable logistic regression analysis for predicting the probability of favorable outcome (H-B grade I-II) for Bell palsy are given in Table 2. Compared with patients who received combination antiviral therapy, those who received only supportive care had lower odds of having a favorable outcome (OR, 0.47; 95% CI, 0.17-1.26). However, the CI was wide, indicating low precision of this estimate, and included the null value; therefore, no definitive conclusion could be made.

Table 2. Multivariable Logistic Regression Analysis for Favorable Outcome for Bell Palsy^a.

Variable	OR (95% CI)
Gender
Male	1.04 (0.78-1.38)
Female	1 [Reference]
Age, y
<40	1.56 (1.09-2.22)
≥40	1 [Reference]
Initial H-B grade
III-IV	2.62 (1.93-3.57)
V-VI	1 [Reference]
Electroneurography results
≥10% (Good)	1.29 (0.73-2.28)
<10% (Poor)	1 [Reference]
Electromyography resultsb
Good	3.38 (2.48-4.61)
Poor	1 [Reference]
Controlled hypertension
Yes	1.64 (1.16-2.33)
No	1 [Reference]
Diabetes
No	1.43 (1.04-2.36)
Yes	1 [Reference]
Treatment method
Oral corticosteroids only	1.13 (0.82-1.54)
Combination antiviral therapy	1 [Reference]
Only supportive care	0.47 (0.17-1.26)

Abbreviations: H-B, House-Brackmann; OR, odds ratio.

^aFavorable outcome was defined as an H-B grade of II or lower.

^bGood electromyography results were defined as the absence of pathologic spontaneous fibrillation activity.

Discussion

Several factors were evaluated, including age, sex, initial H-B grade, underlying disease, such as hypertension and diabetes, electrophysiological test findings, and treatment method. Several previous studies have reported on factors associated with better outcomes in patients with Bell palsy. Peitersen⁸ reported that patient age at the time of complete or incomplete paralysis was associated with treatment outcome for Bell palsy. Children younger than 14 years had a favorable outcome, and older patients had the worst outcome. However, other studies have found that age was not associated with treatment outcome of Bell palsy. Takemoto et al¹⁷ reported little correlation between age and treatment outcome. Mantsopoulos et al¹⁸ also showed that age was not a significant prognostic factor for a favorable outcome in Bell palsy. The association between age and outcome of Bell palsy may seem to be controversial; age less than 40 years was associated with favorable outcomes in this study.

The present study used the H-B grading system, which is most frequently used to assess the degree of facial function in Bell palsy. In other studies,^19,20,21 H-B grade I was set as the threshold for a favorable outcome according to stricter criteria; in the present study, an H-B grade of II or lower is believed to indicate favorable outcomes in the context of normal function in daily life.^19,22 Fujiwara et al²³ reported that the facial grading score at 1 week after treatment was associated with an unfavorable outcome of Bell palsy at 6 months. They examined clinical variables associated with long-term outcomes in patients with idiopathic facial nerve paralysis, including the Yanagihara facial grading system. Mantsopoulos et al¹⁸ reported that the most important factor in the long-term outcome (2-6 years) after the idiopathic nerve paralysis was the initial severity of facial weakness. In our study, the results were consistent with those of previous reports; patients with Bell palsy had favorable outcomes when the initial H-B grade was IV or lower.

Generally, uncontrolled hypertension is associated with facial palsy. The association between severe hypertension and peripheral facial palsy has been described primarily in children. Arterial hypertension is diagnosed after a substantial delay. Adequate antihypertensive treatment is associated with a favorable outcome, and prognosis is good in patients with hypertension controlled by medication.²⁴ Hypertension may increase the risk of Bell palsy among patients aged older than 40 years.²⁵ Controlled hypertension was a major factor for favorable outcomes in patients with Bell palsy.²⁶ It has long been reported that hemorrhages into the facial canal are responsible for facial paralysis with severe hypertension.^27,28 Previous studies have shown that the incidence of Bell palsy is higher in patients with uncontrolled hypertension owing to poor compliance with medication. In 3 adult case studies with known chronic hypertension, facial palsy occurred during the exacerbation of the hypertension owing to nonadherence of medication.^29,30,31 Facial palsy immediately resolved after better blood pressure control, suggesting an association between the controlled hypertension and resolution of facial palsy. Lee et al²⁶ demonstrated that the initial severity of the facial paralysis and controlled hypertension were factors associated with favorable outcome. In the present study, appropriate control of blood pressure owing to adequate antihypertensive treatment was associated with a good outcome after the development of facial palsy.

Diabetes has been reported to contribute to a poor outcome in patients with Bell palsy. Takemoto et al¹⁷ found that diabetes was significantly associated with unfavorable outcome. Moreover, Peitersen⁸ showed that vascular insufficiency and diabetic polyneuropathy were associated with poorer outcomes. Long-term hyperglycemia in patients with diabetes is known to affect the facial nerve fibers, which could cause considerable delays in the blink reflex on both sides of the face.^32,33 This finding suggests that diabetes may have negative consequences on outcomes in patients’ peripheral facial paralysis. The present study demonstrated that the OR for favorable outcomes was higher in patients without diabetes than in those with diabetes. Moreover, we found that the absence of diabetes was statistically significantly associated with favorable outcomes.

Electrophysiological tests, such as ENoG and EMG, were originally introduced by Esslen and Fisch.^34,35 Both tests have been used to assess the severity of facial nerve injury and are electrophysiological measures that indirectly quantify the facial nerve function by recording the motor unit action potentials and/or compound muscle action potentials.³⁶ By comparing the peak-to-peak amplitude of the compound muscle action potentials from the affected side with the response amplitude from the nonaffected side, an estimate of the amount of the degenerated nerve could be presented. Electroneurography is useful for investigating the risk of poor outcomes in the early stages of acute facial palsy. In patients with Bell palsy, ENoG combined with a conduction block and assessment of axonal degeneration can be used to evaluate the degenerated portion of the axons.³⁵ It is considered the most valuable test for investigating the risk of unfavorable outcomes in patients with Bell palsy.^17,18,37 Patients with more than 90% degeneration on the affected side within 14 days after onset of facial paralysis are considered to have poor outcome.¹⁰ The treatment effects were assessed separately in patients with good (ENoG results ≥10%) vs poor (ENoG results <10%) outcomes.^38,39 In the present study, the ENoG was performed at 4 to 5 days after symptom onset, and the needle EMG was performed 2 weeks later. Abnormal ENoG responses, such as wallerian degeneration, usually occur within 72 hours after nerve injury; ENoG should never be performed before that time. Tojima et al³⁷ found that ENoG results could reveal the extent of wallerian degeneration 7 days after symptom onset in patients with Bell palsy. In the present study, ENoG was performed at 4 to 5 days after the onset of facial paralysis. Tests performed this soon after onset did not yield clinically meaningful results.

The results of EMG obtained 2 weeks after onset of Bell palsy have been found to be a reliable factor associated with the outcome. In studies showing the use of EMG in treating facial nerve injuries,^40,41 the detection of abnormal spontaneous activity on needle EMG is known to be a factor associated with unfavorable outcomes. Abnormal spontaneous activity, including positive sharp waves and fibrillation potentials, are well accepted as signs of axonal degeneration.⁴² In the present study, the results of EMG performed 2 weeks after the onset of Bell palsy were considered important for assessing outcomes, and this finding is consistent with those of other studies.^36,43

To our knowledge, no definitive treatment guidelines have been established for Bell palsy owing to the high spontaneous recovery rate (up to 85.2%) and unknown cause.¹³ The American Academy of Otolaryngology treatment guidelines for Bell palsy suggest that treatment with oral corticosteroids within 72 hours of symptom onset is highly likely to be effective in patients with new-onset Bell palsy with or without the use of concurrent antiviral therapy.² Although there is a consensus that early use of prednisolone is effective, prescription of antiviral agents remains controversial. The treatment effect of prednisolone suggests that inflammation by neural edema of the facial nerve is part of the pathogenesis in Bell palsy.⁴⁴

The use of additional antiviral treatment is based on the hypothesis that a simple herpes virus infection could cause inflammation of the facial nerve. Antiviral agents cannot destroy viruses that have already replicated; these drugs inhibit viral replication by interfering with the viral DNA polymerase. Numerous studies that have compared glucocorticoid treatment with placebo in patients with Bell palsy have demonstrated considerable improvement in symptoms with the use of glucocorticoids. Sullivan and colleagues¹³ performed a large, randomized, controlled, and double-blind study with predefined and specified outcome measures and a follow-up at 9 months. They noted that an antiviral agent was not beneficial in improving outcomes of facial paralysis. Engström et al²⁰ aimed to compare the efficacy of prednisolone and valacyclovir for resolution of facial paralysis. They concluded that treatment with prednisolone alone reduced the time to resolution of symptoms, whereas valacyclovir did not, indicating that prednisolone alone is sufficient to treat patients with Bell palsy. In contrast, Hato et al⁴⁵ reported that combination antiviral therapy was more effective in treating Bell palsy, excluding zoster sine herpete, than the conventional prednisolone therapy and described the importance of an early treatment with valacyclovir and prednisolone. This result is in accordance with those of a previous study by Adour and colleagues⁴⁶ who showed that treatment with acyclovir-prednisone is superior to that with prednisone alone in treating patients with Bell palsy.

In discussing the treatment effects of antiviral agents, several factors should be considered. In the study by Hato et al,⁴⁵ the mean Yanagihara score was approximately 15, which corresponds to H-B grades IV and V. The study also examined patients with more severe facial paralysis compared with of the patients in the study by Sullivan et al,¹³ who had a mean H-B grade of 3.6 of 6. The Yanagihara facial nerve grading system⁴⁷ was developed as a representative regional scale in Japan and was standardized to facial function classes in Japan and several other countries. The Yanagihara system measures 10 individual aspects of various facial functions. The score for each feature can be 0 (complete palsy), 2 (partial palsy), or 4 (almost normal), with a maximum total score of 40. The total score provides information on the degree of facial nerve dysfunction. The patients in the study by Sullivan et al¹³ seemed to have milder facial palsy than those in the study by Hato et al.⁴⁵ The mean H-B grade for the patients in our study was similar to the mean H-B grade in the study by Sullivan et al¹³ (3.59 vs 3.6) In addition, Engström et al²⁰ reported that only 30% of patients (245 of 829) had severe palsy (H-B grade ≥V), and the H-B grade in patients treated with prednisolone plus placebo and prednisolone plus valacyclovir were 3.7 and 3.8, respectively. In the present study, the proportion of patients with severe palsy (H-B grade ≥V) was 22.8%, suggesting that the different outcome might be attributed to the large proportion of patients with mild to moderate Bell palsy. de Ru et al⁴⁸ also reported that a large number of patients with mild paralysis recovered spontaneously, and the positive treatment effect of the antiviral drugs may have been diluted. If the study included only those patients with severe Bell palsy, the combination of corticosteroid and antiviral agents might have been different. Some studies suggested that the combination of corticosteroid and antiviral agents is more effective than corticosteroids alone, particularly in patients with severe Bell palsy. Lee et al⁴⁹ showed that combined treatment with a corticosteroid and an antiviral agent (prednisolone plus famciclovir) resulted in better outcomes than those of corticosteroid treatment alone for treating severe Bell palsy (H-B grade ≥V). In the present study, multivariable logistic regression analyses revealed that treatment with corticosteroids alone was associated with a slightly higher odds (1.13) of favorable outcome than the combination antiviral therapy (1.13 [95% CI, 0.82-1.54] vs 1.00 [reference]), and the upper bound of the CI (1.54) suggested that the true difference may be clinically meaningful. Because the lower bound of the CI was 0.82, combination antiviral therapy could also be more beneficial than corticosteroids alone. Thus, these results indicate that a prospective, randomized, controlled, double-blind study with adequate sample size to detect clinically meaningful differences between treatments should be conducted for patients with severe Bell palsy.

The present study investigated the factors associated with favorable outcomes in patients with Bell palsy. Many studies evaluated the association between several factors and outcomes of Bell palsy. Prior studies that included larger numbers of patients than those included in the present analysis were meta-analyses. Therefore, intervariability in the assessment process may be lower in our monocentric study. To our knowledge, few studies with more than 1300 patients have been conducted on the outcomes of Bell palsy.

Strengths and Limitations

A strength of our study was its presentation of factors, baseline characteristics, and outcomes for a large number of patients assessed for more than 10 years. This study also has some limitations. First, we performed the ENoG at 4 to 5 days after symptom onset. The timing of the ENoG testing, one of the important factors associated with outcomes of Bell palsy, was not properly implemented. Second, we could not conduct a double-blind, placebo-controlled, randomized study to evaluate the effectiveness of the treatment method. Because of its retrospective design, the analysis of the optimal method for treating patients with Bell palsy was inferior to that of high-quality randomized clinical trials. Furthermore, although the initial severity of Bell palsy was assessed by 3 otolaryngologists, the evaluators were not blinded, which may have introduced selection bias. Third, we used the H-B grading system to assess the severity of palsy, but, we did not evaluate synkinesis, a risk factor for poor outcome and a major complications of Bell palsy. To overcome these limitations, further research is needed to validate our results on the effectiveness of the treatments for idiopathic peripheral facial palsy.

Conclusions

The rate of favorable outcome (H-B grade ≤II) in patients with Bell palsy was 80.6%. Multiple clinical factors were associated with favorable outcomes in patients with Bell palsy, including younger age, lower initial H-B grade, good EMG result, absence of diabetes, and control of hypertension. Therefore, the present study may help identify patients likely to have favorable outcomes based on specific factors, which may aid clinicians in selecting patients for therapeutic clinical trials.