The facial nerve is the 7th cranial nerve. It has 5 major branches which may be recalled by “To Zansibar By Motor Car” = temporal, zygomatic, bucal, mandibular and cervical branches.
The functions of the facial nerve are:
- Motor control of muscles of facial expression
- Innervation of stapedius in ear
- Supply of submandibular, parotid and sublingual glands
- Efferent limb of corneal reflex
- Taste sensation to anterior two-thirds of tongue
Unilateral facial nerve palsy
Unilateral facial nerve palsy is primary (idiopathic) in 75% of cases. It is then known as Bells Palsy.
Secondary facial nerve palsy is less common (25% of cases).
Causes include:
- diabetes
- pontine infarct
- infection – herpes simplex, varicella zoster (=Ramsey Hunt Syndrome), otitis media, syphilis
- MS
- Neurosarcoidosis
- Tumour
- Trauma
- GBS
- MG
- Drugs – interferon, linezolid
Bells Palsy
Bell’s Palsy is characterised by:
- Unilateral facial weakness
- Pain behind the ear/aural fullness
- Absent taste sensation to anterior two-thirds of tongue
Although Bell’s Palsy is ‘idiopathic’ it is hypothesised to be linked to viral infection.
Incidence is 20 per 100000
Peak onset is between 15 and 45 yrs of age
Both genders are equally affected
Management of Bells Palsy is:
- Protect the eye from drying out
- Steroids – prednisolone 1mg/kg
- aciclovir
Prognosis is generally good – around 90% make a fully recovery, and 85% report some improvement in the first 3 weeks.
Bilateral facial nerve palsy
Consider GBS, diabetes, infection, neurosarcoidosis.
Small print gem: Some subsequently suffer from 'crocodile tears' = eating stimulates unilateral lacrimination instead of salivation.
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