Bells Palsy
Bells Palsy
Bells Palsy
Bell’s Palsy
J J Halperin, Overlook Hospital – Atlantic Health, decompression of all or part of the nerve, to psycho-
Summit, NJ, USA logical counseling, to numerous points in between.
ã 2009 Elsevier Ltd. All rights reserved. The facial nerve’s anatomy is complex (schematically
shown in Figure 1) both functionally and anatomically.
Originating in a nucleus in the pontine tegmen-
tum, the motor fibers take a looping dorsal, then
Introduction ventral, course around the 6th nerve nucleus, joining
Each cranial nerve has its own idiosyncratic propen- fibers connecting to the nucleus solitarius and lacrimal
sity to damage, dictated at least in part by its anatomy. and superior salivary parasympathetic nuclei as they
The fine filamentous nature of the trochlear (4th) travel. Fibers exit the brain stem and travel adjacent to
nerve makes it susceptible in minor head injury. the 8th nerve in the cerebellopontine angle, cross the
The long intracranial course of the abducens (6th) subarachnoid space, enter the internal auditory mea-
puts it at risk with any increase in intracranial pres- tus, and then traverse the longest, most complex
sure. The facial nerve (7th) has a particularly lengthy intraosseous course of any nerve in the body. Through-
and complex course, crossing the subarachnoid space, out its course, components come and go. At the level
winding through a long, narrow bony canal, exiting to of the geniculate ganglion, parasympathetic fibers
cross through the parotid gland; it should not be (which exit the brain stem in the anatomically distinct
surprising that it can be affected in a variety of circum- nervus intermedius) form the greater petrosal nerve
stances. That the detailed pathophysiology of facial and project to the pterygopalatine ganglion, from
nerve palsy remains unclear – over 185 years after which postganglionic fibers pass to the lacrimal gland
its initial description – is remarkable. However the and to the blood vessels of the Circle of Willis. Damage
facial nerve’s peculiar anatomy must contribute to its to this branch results in disorders of lacrimation –
particular susceptibility to damage. either increases or decreases. Clinical interpretation
In recent years the number of disorders clearly of these changes is often confounded in facial nerve
associated with the facial nerve has increased to palsy by the equally important contribution of mech-
include sarcoidosis, Lyme disease, HIV, and herpes anical exposure of the eye, which in and of itself can
(zoster and simplex) infections, yet pathophysiologic lead either to increased tearing from irritation or to
insights remain frustratingly limited. The therapeutic exposure-related drying.
approach similarly has expanded, but each approach Other parasympathetic fibers continue with the
remains controversial. The following overview will main trunk of the facial nerve, to emerge slightly
attempt to summarize what is known, and elucidate more peripherally and contribute to the chorda
these controversies. tympani, through which fibers project to the sub-
mandibular ganglion, with postganglionic projec-
tions to the salivary nuclei. Neurons of the geniculate
Background
ganglion convey sensory input from the nasopharynx,
Sir Charles Bell (1774–1842), a gifted Scottish-born tympanic membrane, and the ear canal. Although these
surgeon, anatomist, and illustrator, described the fibers travel with the facial nerve, they ultimately proj-
course of the facial nerve, and the peculiar ‘blight’ ect to the primary sensory nucleus of V and the nucleus
that befalls it, in 1821. Interestingly, this arguably was of the spinal tract of the trigeminal nerve.
one of his lesser accomplishments. The first Professor Distal to the geniculate ganglion and the greater
of Anatomy and Surgery of the College of Surgeons in petrosal nerve, a small motor branch exits to inner-
London, and the first Professor of Physiology at King’s vate the stapedius muscle. Damage to this results in
College, University of London, among his noteworthy hyperacusis. Shortly thereafter, the chorda tympani
neurologic accomplishments was introducing the con- joins the nerve. This bundle, which, as mentioned,
cept that motor and sensory functions were segregated carries efferent preganglionic parasympathetic fibers
in the spinal roots! Also responsible for describing destined to control salivary glands, also contains
‘Bell’s phenomenon,’ he is, however, best memoria- fibers of the lingual nerve, conveying taste sensation
lized in the eponym for a ‘palsy’ (perhaps a somewhat from the anterior two-thirds of the tongue. Cell bodies
dubious honor). Over the years, many have described of these neurons also reside in the geniculate ganglion;
the clinical concomitants of Bell’s palsy. Proposed fibers project centrally via the nervus intermedius to
therapeutic interventions have ranged from surgical the nucleus solitarius. The fibers that remain distal
156 Bell’s Palsy
perception – in some this may be due to decreased to increase the likelihood of incomplete recovery,
salivation but more often it is a true dysgeusia. Prov- whether the incidence is increased among hyperten-
ing this requires testing taste on the two sides of the sives is unclear. Pregnancy has been reported as a risk
anterior tongue, without allowing the patient to factor, but results have been conflicting; the most sys-
retract the tongue back into the mouth between tematic studies have failed to support this association.
tests, since diffusion of the test substance will immedi- Incidence is increased in patients with sarcoidosis, in
ately invalidate the test. Patients often describe numb- whom involvement can be meningeal, within the
ness on the affected side of the face, but objective parotid, or at points in between. Similarly, incidence
testing rarely confirms this. Most likely this represents is increased in HIV and Lyme infection. When bilateral
misperception of proprioceptive input with attempted facial palsy occurs it may be indicative of the Guillain–
motion of the paralyzed facial muscles. Barré syndrome, sarcoidosis, or Lyme disease.
Recovery is complete in the vast majority
(80–85%) of patients with Bell’s palsy. The degree of
Epidemiology
improvement is commonly graded with the House and
The terms ‘facial palsy’ and ‘Bell’s palsy’ are not Brackmann Grading Scale (Table 1). More extensive
synonymous – the latter term is usually restricted to lesions tend to predispose to incomplete recovery –
patients with idiopathic acute deficits of the facial presence of pain in addition to the retroauricular
nerve.This definition is selected to exclude slowly evol- pain, complete facial paralysis, tearing changes, and
ving facial nerve lesions such as those due to posterior sensory changes are all associated with incomplete
fossa or skull base tumors, as well as brain stem strokes, recovery. Incomplete recovery is somewhat more
skull base fractures, meningitis-associated multiple common among those over 55 years of age. In the
cranial neuropathies, Ramsay Hunt syndrome, etc. most extensive study of this, complete recovery
However, this definition now becomes problematic, occurred in 90% of those under 55 years and 79% of
since there are quite suggestive data that in many those 55 years and older. Although several comorbid-
instances Bell’s palsy is caused by herpes simplex ities are linked to Bell’s palsy, only hypertension is
virus. Since these cases are no longer idiopathic, must associated with a somewhat worse prognosis.
they be removed from those considered to be Bell’s Interestingly, when all of these factors were consid-
palsy? What about patients with facial nerve palsies ered in a multivariate analysis, only complete para-
associated with diabetes or with Lyme disease? Clearly, lysis, non-ear pain, and hypertension were found to
at some point this more than semantic issue will require predict a somewhat worse prognosis. Other factors,
resolution; for now, cases associated with herpes sim- such as age, and other neurologic changes apparently
plex, Lyme disease, and diabetes are generally included merely reflected the impact of these three factors.
as Bell’s palsy. Among patients with none of these risk factors,
The reported incidence of Bell’s palsy varies some- complete recovery occurred in 96%. With an overall
what, but is generally felt to be about 20–25 cases per spontaneous recovery rate of about 85%, and 96%
100 000 population per year, affecting about 1 in among low-risk patients, it is not difficult to under-
60–70 individuals in their lifetime. The disorder is stand why it has been so difficult to determine efficacy
quite infrequent under the age of 10 years, increases of different treatment strategies, and why their use has
by decade from ages 10 to 39 years, is fairly constant been controversial.
at about 35 cases per 100 000 from ages 40 to 69 years,
then increases to over 50 per 100 000 (10 times the
childhood incidence) in those over 70 years. There is
Pathophysiology
no significant male: female or side-to-side difference.
Involvement is bilateral occasionally; in about 6% Understanding the mechanism underlying this mono-
of cases it can be recurrent (the recurrence occurring neuropathy has been challenging. A few autopsy
on either the previously affected or unaffected side). cases, published many years ago, were felt to demon-
The paralysis is complete in a significant proportion strate inflammatory changes in the affected nerve.
of patients, estimates ranging from 45% to 70% in Subsequent review raised the possibility that the
different series. (The former number, from a popula- observed changes were merely what one would expect
tion-based study in Rochester, MN, probably reflects a to see as part of Wallerian degeneration in a nerve
number as free of selection bias as possible.) No damaged more proximally. Surgical series reported
seasonal or geographic clustering has been evident. swollen-appearing nerves – since it is relatively uncom-
Bell’s palsy probably occurs with increased fre- mon to explore normal facial nerves, subsequent
quency in diabetics. Hypertension has also been authors, including Sunderland, have suggested that
considered a risk factor. Although it does appear this was merely the nerve’s normal appearance.
158 Bell’s Palsy
From House JW and Brackmann DE (1985) Facial nerve grading system. Otolaryngology – Head and Neck Surgery 93: 146–147.
Neurophysiologic observations have not been as damage). The highly redundant vascular supply of
informative as one might wish. The standard method the facial nerve generally makes widespread ischemia
used, electroneurography, consists of stimulating the seem unlikely, but such focal ischemia is somewhat
facial nerve at the stylomastoid foramen, recording more plausible.
the compound muscle action potential on the face in a Recent work has implicated several specific in-
way designed to span several muscles (a method that fections in the etiology of facial nerve palsy. Lyme
can lead to unpredictable summation of the com- disease, infection with the tick-borne spirochete Borre-
pound muscle action potentials of different muscles), lia burgdorferi, clearly is associated with facial nerve
and comparing the amplitude ratio of the affected lesions, which may be bilateral in as many as 25% of
side to the unaffected side. In many series, only such cases. The pathophysiology is unclear. This does
patients with no elicitable response are sent to a not appear to be due to a meningeal process, even
neurologist or electromyographer. More sophisticated though Lyme disease can cause meningitis. Neurophy-
neurophysiologic studies suggest nerve demyelination siologic studies suggest that this is due to a mononeur-
in milder cases, with significant axonal damage when itis multiplex, although the precise mechanism
the paralysis is severe. underlying this is unclear.
Anatomic studies have suggested that the meatal One of the most interesting sets of findings in the
foramen is the narrowest point along the facial past decade has focused on the possible association
nerve’s bony canal; intraoperative neurophysiology between facial nerve palsy and herpes simplex-1 infec-
has suggested that this is the likely site of damage. tion. In one of the best known studies, endoneurial
This has led to the hypothesis that the nerve swells as fluid was obtained – at least 15 days after onset of the
a result of an inciting event and becomes entrapped at lesion – at the time of 7th nerve decompression in
the meatal foramen. Swelling at this confined point 14 patients with unrecovering Bell’s palsy. Eleven of
could either produce focal demyelination and con- the 14 were polymerase chain reaction (PCR) positive
duction block, block axoplasmic transport (resulting for HSV-1. Twelve of 13 tested patients had peripheral
in nerve damage), or lead to intranerve pressures blood serologic evidence of past HSV-1 infection.
exceeding perfusion pressure (resulting in ischemic Seropositivity and PCR positivity were significantly
Bell’s Palsy 159
timing of treatment within this window affects the seems very limited. In general, prevention of secondary
likelihood of recovery – a somewhat surprising obser- complications, such as exposure keratitis, dental decay,
vation given that the major nerve damage is thought to and muscle contractures, is the most important aspect
occur in the first 48 h. Notably, a Cochrane analysis of treatment.
questioned the validity of the conclusion that steroids
are effective, because of methodological problems See also: Axonal Injury: Neuronal Responses; Brainstem
with several of the largest included studies. and Cranial Nerves; Electromyography (EMG) and Nerve
Even fewer studies are available concerning use Conduction Studies; Optic Nerve, Optic Chiasm and Optic
of acyclovir. Here, too, a meta-analysis led to the Tracts; Peripheral Nerve Regeneration: An Overview.
conclusion that treating all patients with acyclovir
improved the proportion of patients recovering by
22%. Given the small number of studies available, Further Reading
and their sometimes conflicting conclusions, this was Adour KK, Ruboyianes JM, Von Doersten PG, et al. (1996) Bell’s
felt to be less compelling, but was recommended as Palsy treatment with acyclovir and prednisone compared with
appropriate treatment. Again, the fact that this treat- prednisone alone: A double blind, randomized, controlled trial.
ment is usually given – and appears to be effective – at Annals of Otology, Rhinology and Laryngology 105: 371–378.
Adour KK, Wingerd J, Bell DN, et al. (1972) Prednisone treatment
a time that maximal nerve damage has already
for idiopathic facial paralysis. New England Journal of
occurred is theoretically puzzling. Medicine 287: 1268–1272.
Finally, with regard to decompressive surgery, the Gantz BJ, Rubinstein JT, Gidley P, et al. (1999) Surgical manage-
task force found no scientifically compelling study. ment of Bell’s palsy. Laryngoscope 109: 1177–1188.
While earlier studies were negative, one more recent Gilden DH (2004) Bell’s palsy. New England Journal of Medicine
study of patients in whom recovery was thought to be 351: 1323–1331.
Grogan PM and Gronseth GS (2001) Practice parameter: Steroids,
extremely unlikely by clinical and EMG criteria, who acyclovir, and surgery for Bell’s palsy (an evidence based
underwent a far more extensive decompression extend- review). Neurology 56: 830–836.
ing to the meatal foramen, provided encouraging Halperin JJ (2003) Facial nerve palsy associated with Lyme disease.
results, with 91% of patients improving significantly Muscle & Nerve 28: 516–517.
(but with no controls). House JW and Brackmann DE (1985) Facial nerve grading system.
Otalaryngology – Head and Neck Surgery 93: 146–147.
Overall, the likelihood of recovery is great, appar- Katusic SK, Beard CM, Widerholt WC, et al. (1986) Incidence,
ently enhanced with early treatment with corticoster- clinical features and prognosis in Bell’s palsy, Rochester,
oids and/or acyclovir-like antivirals. In the appropriate Minnesota 1968–1982. Annals of Neurology 20: 622–627.
setting, potentially contributing disorders such as Lyme Murakami S, Mizobuchi M, Nakashiro Y, et al. (1996) Bell palsy and
herpes simplex virus: Identification of viral DNA in endoneurial
disease, HIV, or sarcoidosis need to be considered,
fluid and muscle. Annals of Internal Medicine 124: 27–30.
and treated appropriately if found Surgical treat- Salinas R, Alvarez G, and Ferreira J (2004) Corticosteroids for
ment remains unproved, but is occasionally attempted Bell’s palsy (idiopathic facial paralysis). Cochrane Database
in situations in which the likelihood of recovery of Systematic Reviews 4: CD001942.