Facial nerve conduction study in the prognosis of Bell’s palsy outcomes by using Facial Nerve Grading System 2.0

Journal of military pharmaco-medicine no5-2018

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
th
the 20 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
th
(55.2%). On the 20 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
th
difference 75% or higher on 20 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 ()
Date received: 29/03/2018
Date accepted: 21/03/2018

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Journal of military pharmaco-medicine no5-2018

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

Slight
weakness >
75% of normal

Slight
weakness >
75% of normal

Slight synkinesis,
minimal
contracture

Slight
weakness >
75% of normal

Slight
weakness >
75% of normal

Resting
symmetry

Resting
symmetry

Obvious
synkinesis, mild
to moderate
contracture

Asymmetry at rest
< 50% of normal

Asymmetry at
rest < 50% of
normal

Asymmetry at
rest < 50% of
normal

Complete closure
with mild effort
3

Obvious
weakness >
50% of normal
Resting
symmetry

4

Asymmetry at
rest < 50% of
normal

Slight weakness >
75% of normal
Complete closure
with maximal effort

Cannot close
completely
5

Trace
movement

Trace movement

Trace
movement

Trace
movement

6

No movement

No movement

No movement

No movement

Disfiguring
synkinesis,
severe
contracture

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Journal of military pharmaco-medicine no5-2018
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
190

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

25

21
20
15
10
6
5

2
0

0
Amplitude difference < 75%
Amplitude difference >= 75%
Figure 1: Relationship between FNGS 2.0 grade on the day 40 and CMAP amplitude
difference on the day 20.
FNGS 2.0 grade I, II
FNGS 2.0 grade 3 or higher
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.
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%

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.
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Journal of military pharmaco-medicine no5-2018
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
192

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.
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