Bell’s Palsy
Bell’s palsy is an idiopathic, unilateral facial nerve (cranial nerve VII) palsy with rapid onset.
This updated UKMLA guide to Bell’s palsy is based on NICE CKS, which covers causes, risk factors, symptoms, diagnosis and management.
Causes and Risk Factors
Bell’s palsy is idiopathic
- Facial nerve palsy may be due to inflammation and oedema
- Herpes simplex virus, herpes zoster virus, and autoimmunity may contribute to the development of Bell’s palsy, but the exact pathogenesis is controversial, and the significance of these factors remains unclear
Risk factors:
- 15-45 y/o
- Pregnancy (esp. 3rd trimester and first 2 weeks postpartum) – 2-4x risk
- Diabetes
- Immunocompromised
- Obesity
- Hypertension
- Upper respiratory conditions
Clinical Features
Rapid onset (<72 hours) of unilateral facial muscle weakness / paralysis
- Reduction or loss of movement on the affected side
- Sagging of the eyelid / corner of the mouth
- Drooping of the eyebrow / corner of the mouth
- Loss of nasolabial fold
- On examination: weakness or paralysis of ipsilateral upper and lower facial muscles, affecting facial expression such as
- Raising the eyebrow
- Closing the eye tightly
- Smiling
- Puffing out the cheeks
Other features:
- Eye
- Dry eyes (30%), eye pain, excessive tearing
- Poor / incomplete eye closure
- Ear
- Post-auricular and ear pain (~50%)
- Hyperacusis (<5%)
- Mouth
- Change in taste (~35%)
- Difficulty chewing and dry mouth (~20%)
Relevant anatomy of the facial nerve (CN VII)
Facial nerve innervates:
- Muscles of facial expression (forehead, eyelids, cheeks, lips and mouth)
- Orbicularis oculi (responsible for eye closure)
- Anterior 2/3 of the tongue via the chorda tympani branch (responsible for taste)
- Parasympathetic supply to lacrimal and salivary glands (greater petrosal nerve)
- Nerve to stapedius muscle (responsible for the stapedial reflex)
- Sensory fibres to part of the external ear
In Bell’s palsy, there should be no features suggestive of an alternative neurological diagnosis.
There should be no:
- Facial sensory loss – Bell’s palsy causes facial weakness, not loss of facial sensation (which is innervated by the CN V, not CN VII)
- Limb weakness and sensory loss
- Dysphasia
- Neglect
- Visual field defect
Differential Diagnosis
The most important differential diagnosis of Bell’s palsy is a UMN facial weakness, such as from a stroke or other intracranial lesion affecting the corticobulbar pathway
| Features suggestive of LMN facial weakness (e.g. Bell’s palsy) | Features suggestive of UMN facial weakness (e.g. stroke) |
|---|---|
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Rationale on forehead sparing in UMN facial weakness:
However, in an LMN lesion (e.g. Bell’s palsy) the lesion occurs at or distal to the facial nucleus, affecting the facial nerve after cortical input has already converged. Therefore, even though the forehead receives bilateral cortical input, the final motor pathway to the ipsilateral forehead is interrupted. |
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Note a brainstem stroke can produce an LMN facial weakness. Therefore, forehead involvement does NOT completely exclude a stroke, esp. if there are focal neurological deficits.
Ramsay Hunt syndrome
- Caused by reactivation of VZV in the geniculate ganglion of the facial nerve (CN VII)
- Causes an unilateral, ipsilateral LMN facial nerve palsy, affecting both the upper and lower face (just like in Bell’s palsy)
- Presence of additional features help distinguish it from Bell’s palsy, including:
- Vesicular rash on the ear (esp. pinna), ear canal, or pharynx
- Severe ear pain
- Possible CN VIII involvement, causing sensorineural hearing loss, tinnitus and vertigo
Other differentials:
- Guillain-Barre syndrome, sarcoidosis and Lyme disease can cause CN VII palsy (typically bilateral but unilateral possible)
- Multiple sclerosis
- Facial nerve tumour / parotid gland tumour
Investigation and Diagnosis
Bell’s palsy is a clinical diagnosis, after excluding alternative causes of facial weakness or paralysis
Laboratory tests and imaging are NOT necessary for clinically diagnosed Bell’s palsy
Management
Referral Criteria
Refer urgently if ANY of the following are present:
- Facial nerve palsy may be caused by UMN cause or cancer or trauma
- No improvement after 3 weeks of treatment
- Incomplete recovery after 3 months of onset
- Worsening / new neurological findings
Red flags for possible UMN cause:
- Facial sensory loss
- Limb weakness and sensory loss
- Dysphasia
- Neglect
- Visual field defect
General Advice / Conservative Management
Advise that most patients begin to recover, even without treatment, within 2-3 weeks. Complete recovery usually occurs within 3-4 months
Advice on eye care:
- Keep the affected eye lubricated (eye drops during the day and eye ointment at night)
- Tape the eye closed at night if the patient is unable to close the eye
- Eye patches are contraindicated as the eye may open under the patch, leading to corneal abrasion
- Wear sunglasses when outdoors
- Avoid activities that may irritate the eye (e.g. swimming and dusty environments)
Pharmacological Management
Consider oral prednisolone if the patient presents within <72 hours of onset
- 50 mg daily for 10 days OR
- 60 mg daily for 5 days followed by a daily reduction in dose of 10 mg (for a total treatment time of 10 days)
Antivirals alone are NOT recommended for Bell’s palsy.
Antiviral treatment in combination with a corticosteroid may be of small benefit, but seek specialist advice if this is being considered.