Bellu2019s Palsy Aetiology Classification Differential

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REVIEW ARTICLE
Bell’s Palsy : Aetiology, Classification, Differential
Diagnosis and Treatment Consideration : A Review
Kavita Nitish Garg*, Khushboo Gupta*, Saurabh Singh**, Sanjeev Chaudhary
Abstract
Bell’s palsy (spontaneous idiopathic facial paralysis), which is the most common facial nerve
disease, has a sudden onset. Bell’s palsy is the most common cause of facial paralysis, accounting
for 70 per cent of facial palsies, when other causes have been eliminated. It has an incidence of 11-
40 per 100,000 per year, and most commonly occurs in females in their teens and twenties. The
distribution is almost equal in the thirties, with a slight predominance in males over 40.The annual
incidence of Bell’s palsy in the Western world is approximately 20/l 00 000. Untreated Bell’s palsy
leaves some patients with major facial dysfunction and a reduced quality of life.It is essential to rule
out other causes of facial paralysis before making definitive diagnosis, which implies the
intervention. Bell’s palsy has been termed a diagnosis of exclusion. This review emphasizes the
etiology, diagnosis and management of patients with Bell’s palsy.
(Garg KN, Gupta K, Singh S, Chaudhary S. Bell’s Palsy : Aetiology, Classification, Differential Diagnosis and
Treatment Consideration : A Review. www.journalofdentofacialsciences.com, 2012; 1(1): 1-8)
Key words: Bell’s palsy, facial paralysis, facial dysfunction.
Introduction
Facial nerve palsy results in the loss of facial
expression and is most commonly caused by a
benign self- limiting inflammatory condition known
as Bell’s palsy (BP).
1
BP is a condition
characterized by an acute onset of facial nerve
palsy with no known cause. The incidence is about
20/year/100,000 population
2
, and leads to a
considerable disturbance in social activities among
patients.
3
Although the actual cause of BP is
unknown, the widely accepted mechanism is
inflammation of the facial nerve during its course
through the bony labyrinthine part of the facial
canal, which leads to compression and
demyelination of the axons, and disruption of
blood supply to the nerve itself
4
.
BP is defined as a lower motor neuron palsy of
acute onset and idiopathic origin.
5
BP is regarded
as a benign common neurological disorder of
unknown cause. It has an acute onset and is
almost always a mononeuritis
6
. The facial nerve is
*Senior Resident, Department of Oral & Maxillofacial
Pathology, CSM Medical University, Lucknow
**Consultant, Singh Medical Hospital, Varanasi
***Consultant, Max Hospital, New Delhi
Address for Correspondence:
Senior Resident, Department of Oral & Maxillofacial
Pathology, CSM Medical University, Lucknow
e-mail: drkavitanitish@rediffmail.com
2
Garg et al.
www.journalofdentofacialsciences.com Vol. 1 Issue 1
a mixed cranial nerve with a predominant motor
component which supplies all muscles concerned
with unilateral facial expression. Knowledge of its
course is vital for anatomic localization and clinical
correlation. BP accounts for around 72% of facial
palsies
.
7
Scottish surgeon anatomist Sir Charles
Bell (1774-1842) described this as a syndrome of
complete facial paralysis in a lecture 'On the
nerves: giving an account of some experiments on
their structure and functions, which lead to a new
arrangement of the system' to the Royal Society of
London in 1821. Almost a century later, the
management and aetiology of BP is still a subject
of controversy.
8
History
It was first reported by Nicolas A Friedrich two
century ago in 1798
9
. Sir Charles Bell originally
described this condition in 1821. The term BP is
used to describe an acute-onset, idiopathic facial
paralysis resulting from a dysfunction anywhere
along the peripheral part of the facial nerve from
the level of the pons distally.
10
Epidemiology
The disease is common, with an annual
incidence is reported in Table 1.
11-15
.
Table 1: Incidence rate
Year Annual incidence
1974-82 13-34/ 100,000
1998-2006 20-30/100,000
2001 20/100,000
Etiology
Since BP is a facial paralysis of unknown
origin, it is essential to rule out other causes of
facial paralysis before making the definitive
diagnosis, which implies the intervention. BP has
been termed a diagnosis of exclusion
16
.
The causes include microcirculatory failure of
the vasonervorum, viral infection, ischemic
neuropathy, autoimmune reactions
17-20
surgical
procedure such as local anesthesia
21,22
tooth
extraction
23-25
, infections
26,27
, osteotomies, prepros-
thethic procedures, excision of tumors or cysts,
surgery of TMJ
28,29
and surgical treatment of facial
fractures and cleft lip/palate
30
. A viral cause has
been widely accepted, but no virus has been
consistently isolated in patients with BP. The
evidence for the viral hypothesis has been based
primarily on clinical observation and changes in
viral antibody titers. The pathogenesis of the
paralysis may be a viral neuropathy alone or
ischemic neuropathy caused by a viral infection.
Although acute facial paralysis can occur during
many viral illnesses such as mumps, rubella,
herpes simplex, and Epstein-Barr virus infection or
as a result of the reactivation of the human herpes
virus in the geniculate ganglia.
17-20
Some patients may be more easily predisposed
to facial nerve inflammation by exposure to a
preceding pathogen, such as Herpes simplex virus,
Epstein-Barr virus and cytomegalovirus. There
have been an increasing number of reports on the
Herpes simplex virus particle found on facial nerve
biopsy in patients with BP
31, 32
. Facial nerve
paralysis may be central or peripheral in origin,
complete or incomplete. Its cause is varied and
included trauma, tumor formation, iatrogenic
problems, idiopathic conditions, cerebral infarct,
pseudobulbar palsy and viruses. It results in a
characteristic facial distortion that is determined in
part by the nerves branches involvement
33,34
The literature also reports three mechanisms,
in which a dental procedure could damage a
nervous structure: direct trauma to nerve from a
needle, intraneural hematoma formation or
compression and local anesthetic toxicity. Direct
trauma seems unlikely since many patients report
experiencing trauma to the nerve when they feel
the electric shock sensation on injection of the
needle. However, virtually all these symptoms
resolve completely with no residual nerve
damage.
35
Besides common conditions like
hypertension and diabetes mellitus, which may
predispose to single or multiple attacks.
36
The familial cases of recurrent ipsilateral and
alternating contralateral facial nerve palsy have
both autosomal dominant and recessive
inheritance.
37
This genetic predisposition may also
include variations in the immune response of each
individual towards the inciting antigen.
Clinical features
There are three symptoms commonly noted by
the patient in addition to the facial palsy. Epiphora
Garg et al. 3
www.journalofdentofacialsciences.com Vol. 1 Issue 1
due to lack of tone in the lower eyelid and
consequent failure of the punctum to make contact
with the globe of the eye is often present. Pain is a
frequent complaint, and may be in the ear, spread
more widely over the head, down the neck or into
the eye. It is usually present for a few days and
may precede the palsy for up to 72 hours; but
occasionally it comes on several days after the
palsy and may be severe and persistent.
Tenderness over the stylomastoid foramen may be
present.
38
The other symptoms of BP include pain and
numbness on the affected side of the face,
especially in the temple, mastoid area, and along
the angle of the mandible.
39
The mouth may be
dry due to decreased salivary secretion and altered
taste sensation over the anterior two-thirds of the
tongue and incomplete hyperaesthesia over the
trigeminal nerve distribution
as well as hyperacusis
on the affected side
6, 40
.
Classification
BP has been classified into the following 5
categories according to the clinical course of
disease: unilateral non-recurrent, unilateral
recurrent, simultaneous bilateral, alternating
bilateral or recurrent bilateral
41
.
Differential Diagnosis
The gradual onset and duration of the facial
paralysis with associated facial pain are also
consistent with a space-occupying lesion.
42
In
addition to cases with BP, minimal facial nerve
thickening with contrast attenuation are possible to
be observed also in cases of Guillan Bare
Syndrome, postoperatively, traumatic facial
paralysis and following radiotherapy, Unilateral
central facial weakness (lower face muscles) may
be due to a lesion of the contralateral cortex,
subcortical white matter, or internal capsule. In
addition to facial weakness, symptoms may
include hemiparesis, hemisensory loss, or
hemineglect (severe impairment of spatial
perception).
Lyme neuroborreliosis- The spirochete Borrelia
burgdorferi can affect central nervous system
tissues. Lyme neuroborreliosis should be suspected
in a patient who presents with isolated facial
weakness and who has a history of tick bite with
rash or who lives in an area where Lyme disease is
endemic. Tumors involving the facial nerve
account for fewer than 5% of all cases of facial
nerve paralysis. A tumor should be suspected if
weakness progress over weeks, if a mass is present
in the ear, neck, or parotid gland, and if no
functional improvement is seen within 4 to 6
weeks.
42
BP associated with other disease
Literature reviewed that ‘‘peripheral facial
palsy (PFP)’’, ‘‘chickenpox’’ and ‘‘varicella-zoster
virus’’ to identify case reports of PFP associated
with varicella published from 1980 to January
2008. From 1989 to date, 10 patients with
bilateral Bell palsy associated with acute HIV-1
infection have been described in the literature
(Table II)
43-52
.
Table II: Clinical characteristics of 10
patients with bilateral Bells palsy during
acute HIV-1 infection
Year Case
patient
(Ref.)
Age/
Sex
CD4+
cell
count
cells/
mm
3
CD8+
cell
count
cells/
mm
3
Outcome,
weeks
1989 1 (43) 45 (M) 770 1550 Recovery
(23)
1989 2 (44) 19 (F) 776 958 Recovery (3)
1990 3 (45) 40 (F) N/R 1542 (3)
1993 4 (46) 32 (M) 718 2393 N/R
1993 5 (47) 21 (M) N/R N/R (8)
1995 6 (48) 43 (M) 404 N/R N/R
2000 7 (49) 37 (M) 533 1134 N/R
2002 8 (50) 73 (M) 513 2563 Persistent
Paresia
2003 9 (51) 29 (F) N/D N/D N/R
2006 10 (52) 26 (M) 327 N/R Recovery
(N/R)
N/D- Not done N/R- Not reported
Diagnosis
The proper history and physical examination
provide the key to the diagnosis of BP. Most
patients do not require any laboratory testing.
However, patients who have persistent weakness
4
Garg et al.
www.journalofdentofacialsciences.com Vol. 1 Issue 1
without significant improvement requires further
investigations.
53
1. Imaging: Computed tomography (CT) or MRI
is indicated in cases of, no improvement in
facial paresis even after 1 month, hearing loss,
multiple cranial nerve deficits and signs of limb
paresis or sensory loss.
2. Hearing testing - If hearing loss is suspected,
then audiologic testing can be to rule out
acoustic neuroma.
3. Laboratory testing is necessary if the patient
has signs of systemic involvement without
significant improvement over more than 4
weeks. A number of tests may be helpful.
Complete blood count with differential helps to
rule out lymphoreticular malignancy, the first
manifestation of which may be peripheral facial
palsy
54
. Blood glucose should be measured if
diabetes mellitus is suspected. Serum antibodies
against herpes zoster and B burgdorferi (the agent
of Lyme disease) can be checked if the patient has
signs such as vesicular lesions on the external ear
or lives in an area where Lyme disease is endemic.
Serum calcium and angiotensin-converting
enzyme levels should be tested if sarcoidosis is
suspected; these levels are high in sarcoidosis.
Cerebrospinal fluid testing is helpful if infection
or malignancy is suspected; however, in case of
BP cerebrospinal fluid tends to show mild and
inconsistently elevated cell counts and protein
levels.
Electrodiagnostic testing is not routinely done
in BP. It is not very reliable when BP is in the
initial stages; however, after 2 weeks, it may detect
denervation and demonstrate nerve
regeneration.
55
Management
Treatment of BP is still controversial.
55
Clinical
and electrophysiological assessment should be
done. Clinical evaluation for both the severity of
paralysis and the presence of complication is the
first step before the start of treatment or
rehabilitation. The most popular method for
assessing the severity or paralysis is the facial
nerve grading system according to House and
Brackmann (Table III).
56
For persons with persistent paralysis of the
facial nerve, treatment modalities such as steroid
therapy and surgical nerve decompression have
been prescribed.
57
Most authors agree that 75% of
BP cases regress spontaneously with complete
recovery. Approximately 15% of the cases have
satisfactory recovery with a slightly detectable
neurological deficit and 10% of the cases have
permanent paralysis.
58
A good prognosis is
associated with BP seen in children.
59
Corticosteroids are the most commonly used
agents for reducing inflammation and edema in
the nerve sheath.
60
Table III: Facial nerve grading system
Grade Percent of
Function
Degree of
Function
Mesurement
I 100 - 8/8
II 76-99 Slight 7/8
III 51-75 Moderate 5/8-6/8
IV 26-50 Moderately
Severe
3/8-4/8
V 1-25 Severe 1/8-2/8
VI 0 Total Paralysis 0/8
*A centimeter is divided into four equal parts. On the affected
side of the face, maximal voluntary lateral movement of the
corner of the mouth is measured 0-4, and elevation of the
eyebrow is measured 0-4, resulting in a sum from 0/8 to 8/8
The intake of corticosteroids alone or in
combination with anti viral drugs, improve the
prognosis of BP (i.e. induces rapid and complete
recovery in most of the patients) through
preventing (or minimizing) axonal degeneration of
nerve fibres. CS prevent or lessen nerve oedema
and swelling in the facial bony canal; antiviral drug
suppress viral replication in the neural tissue, thus
they may protect the facial nerve from severe
damage.
61
The route and extent of decompression for
recurrent facial palsy is also controversial. Both
transmastoid subtotal decompression and
combined transmastoid-middle cranial fossa total
decompression approach have been advocated.
62
Early surgery including surgical decompression of
the facial nerve may be recommended within 2
weeks following the onset of BP, if
electroneurography revealed >90% degeneration
Garg et al. 5
www.journalofdentofacialsciences.com Vol. 1 Issue 1
of facial nerve fibres. On other hand, some may
not recommended such surgical intervention in
BP.
63
The commonly used tests include: the
maximum nerve excitability test, the maximum
stimulation test (MST), electroneurography
(ENoG). The MST and ENoG are the most reliable
in predicting prognosis (and assessing the extent of
facial nerve degeneration) if done 7-10 days after
the onset of paralysis. Transcranial magnetic
resolution is still inferior to the above mentioned
techniques. The facial nerve conduction velocity
may be done when side to side comparison is not
possible as in bilateral facial palsy. The blink reflex
is done mainly to exclude the lesion at the pons or
medulla. Electromyography (EMG) of the facial
muscles determines sign of denervation and/or
reinnervation as well as the degree of recruitment
of motor units.
63
Physical treatment: It has also been
recommended to use local superficial heat therapy
(i.e hot packs or infrared rays) for 15min/session
for the facial muscles prior to electrical stimulation.
Massage which has been frequently been
prescribes for facial palsy, improves circulation and
may prevent contracture.
64
Short wave diathermy
(SWD) has been suggested as treatment of BP
however, some may not recommend its use in BP
because there is acute viral inflammation of the
facial nerve in its early stage
57
and heating of
inflamed nerve may be
contraindicated.
65
Acupuncture
66
and magnets
67
have been used in combination with
physiotherapy in the management of facial palsy,
but their specific efficacy needs further
investigation.
Treatment of hyperbaric oxygen, through the
inhalation of 100% oxygen under high pressure (at
pressure 2.8 times greater than normal
atmosphere), should possible be considered as one
of the physical modalities. It was reported that this
modality has induced better recovery than
prednisone treatment in BP patients.
68
Apart from above treatment eye and facial
muscles protection is necessary. For eye
protection, early treatment including use of artifical
tears, night time eye patch ophthalmic ointment
before sleep and eyeglasses are usually used to
protect the light, dust and wind while in long term
treatment, ophthalmic consultation is necessary for
possible surgical interference, if there is a failure of
spontaneous eye closure.
44,57,58
Facial muscle protection from injury may be
achieved by use of porous adhesive tape to
prevent deviation of mouth to the healthy side
during smiling. In case of management of facial
hyperkinesis, when surgery is not indicated, local
injection with botulinum toxin-A seems to be the
most appropriate therapy.
63
They should be
performed while standing in front of a mirror and
include trying to raise the eyebrows, opening and
closing the eyes, blowing, and whistling. These
exercises can be performed a few times daily. The
efficacy of exercise has not been formally
evaluated.
69
Prognosis:
The prognosis depends to a great extent on the
time at which recovery begins. If recovery begins
within one week, 88% obtain full recovery, within
one to two weeks 83% and within two to three
weeks 61%. Early recovery gives a good prognosis
and late recovery a bad prognosis.
70
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