Bell’s palsy
D E F I N I T I ON
Idiopathic lower motor neurone facial (VII) nerve palsy.
AET IOLOGY
Idiopathic. Sixty percent are preceded by an upper respiratory tract infection,
suggesting a viral or post-viral aetiology.
E P IDEMI OLOGY
Annual incidence is 15–40 in 100 000. Most cases: 20–50 year.
H ISTORY
Prodrome of pre-auricular pain in some cases followed by acute (hours/days)
onset unilateral facial weakness and droop. Maximum severity within 1–2 days.
Fifty percent experience facial, neck or ear pain or numbness.
Hypersensitivity to sound (hyperacusis caused by stapedius paralysis).
Loss of taste sense (uncommon).
Tearing or drying of exposed eye.
EXAMI N A T ION
Lower motor neurone weakness of facial muscles (affects all the ipsilateral
muscles of facial expression and does not spare the muscles of the upper part of the face
as seen in UMN facial nerve palsy).
Bell’s phenomenon: Eyeball rolls up but eye remains open when trying to close the eyes.
Although patient may report unilateral facial numbness, clinical testing of sensation is
normal. The ear should be examined to exclude other causes (e.g. otitis media, herpes
zoster infection).
I N V E S T IGATIONS
Usually unnecessary except to exclude other causes, e.g. Lyme serology,
herpes zoster serology.
EMG: May show local axonal conduction block in facial canal. Only useful >1 week after
onset.
MANAGEMENT
Protection of cornea with protective glasses/patches and artificial tears.
High-dose corticosteroids (prednisolone) is beneficial within 72 h (given only if Ramsay
Hunt’s syndrome is excluded). Little evidence for aciclovir.
Surgery: Lateral tarsorrhaphy (suturing the lateral parts of the eyelids together) if imminent or
established corneal damage.
COMPL I C A T IONS
Corneal ulcers, eye infection. Aberrant reinnervation may occur, e.g.
blinking may cause contraction of the angle of the mouth as a result of simultaneous
innervation of obicularis oculi and ori. Parasympathetic fibres may also aberrantly reinnervate
causing ‘crocodile tears’ when salivating.
P ROGNOS I S
Most (85–90%) recover function within 2–12 weeks with or without
treatment.
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