Bell’s Palsy.
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Definition:
Acute Idiopathic Lower Motor Neuron Type of
Facial nerve palsy.
Understanding:
Acute – sudden in onset
Idiopathic – the cause is not known
Lower Motor Neuron – Infranuclear Pathology.
So there will be all features of Lower Motor Neuron type of facial nerve palsy.
Etiology:
Incidence: Bell’s palsy is more in women than in men.
Some literature suggests that it is more common in patients with diabetes.
One of the risk factors also includes Pregnancy.
As already explained the cause of Bell’s palsy is unknown
i.e. idiopathic but there are some theories which suggest some viral or
auto-immune etiology.
Herpes Simplex Virus 1 (HSV1) was frequently detected in endoneurial
fluid and posterior auricular muscle in patients with Bell’s palsy, suggesting
that reactivation of this virus in geniculate ganglion may be responsible for
most of the cases.
Also, reactivation of the varicella-zoster virus is associated with Bell’s Palsy in
up to 1/3rd of the cases.
Clinical Features:
Onset – characteristically Acute (about one-half of cases
attain maximum paralysis within 48 h and practically all within 3 or 4 days).
In most of cases, pain behind the ear may precede the paralysis
by a day or two.
Impairment of taste is present in most patients but it rarely
persists beyond the second week of paralysis.
Hyperacusis can be experienced in the ipsilateral ear which
indicates the involvement of the stapedius muscle.
All features of LMN type of facial palsy will be seen, which
are:
· Drooping of
corner of the mouth.
· Drooling of
saliva from angle of mouth.
· Loss of
nasolabial fold.
· Angle of
mouth deviates to opposite side of the lesion.
· Forehead
involved i.e. unable to raise an eyebrow on the same side of the lesion.
We
already discussed the concept of LMN and UMN facial nerve palsy conceptually in
detail in our previous videos. Link for those videos:
Facial Nerve Basics:
Facial Nerve Clinical Co-relation:
https://www.youtube.com/watch?v=cnuBuskixzA
Then there can also be corneal ulceration due to inability to
close the eye during sleep.
Differential Diagnosis:
First: Ramsay Hunt Syndrome: It is caused by reactivation of
Herpes Zoster in geniculate ganglion characterized by facial nerve palsy
associated with vesicular eruption
in external auditory canal. Often the eighth
cranial nerve is also involved in Ramsay Hunt Syndrome.
Second: Any Middle Ear disease involving 7th nerve
like cholesteatoma.
Third: Acoustic
Neuroma: It is the most common Cerebro-Pontine angle tumor that arise from the Schwann cell sheath of
vestibulocochlear nerve.
The characteristic feature of Acoustic Neuroma is that in MRI it shows ice-cream
cone appearance.
This due to its extension of tumor into the intracanulicular part of the
internal acoustic meatus.
Tumors that invade temporal bone (example: carotid body,
dermoid)
Investigations:
It is usually diagnosed clinically after taking proper
history.
There is no particular diagnostic procedure or tests for
diagnosis of Bell’s Palsy.
MRI often shows swelling and enhancement of the facial nerve.
To rule out alternate diagnosis, appropriate investigations
can be done if needed.
Treatment:
Symptomatic measures: Use of paper tape to depress the upper
eyelid during sleep. Prevent corneal drying by artificial tears.
The course of Prednisolone, given as 60-80 mg daily during the first 5 days and
then tapered over the next 5 days. It shortens the recovery period.
Combination of Prednisolone with anti-virals like acyclovir or valacyclovir has
no added benefit. But if given, the dose should be:
Acyclovir: 400 mg 5 times a day for 10 days or
Valacyclovir 1000 mg daily for 5-7 days.
Prognosis:
Majority of patients recovers very well (>90%) if recovers
starts within a few days.
Poor prognosis is seen if pt. have lost of taste sensations
and hyperacusis.
Those who recover may show signs of anomalous re-innervations
like “crocodile tears”.
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