Bell's palsy
Exam Tips
- Differentiate LMN vs UMN facial weakness: Bell's palsy affects forehead and lower face; stroke classically spares the forehead.
- In OSCEs, always assess and document eye closure and corneal risk first; eye protection is time-critical.
- Bell's palsy is a diagnosis of exclusion: atypical features (gradual onset, recurrent/bilateral palsy, vesicles, parotid mass, other cranial nerves) should trigger urgent specialist referral.
- State the treatment window clearly: start prednisolone within 72 hours for best evidence of benefit.
- Quote prognosis numbers in vivas to demonstrate clinical counselling skill.
Definition
Bell's palsy is an acute idiopathic lower motor neurone palsy of the facial nerve (cranial nerve VII), causing rapid-onset unilateral facial weakness that usually reaches maximum severity within 72 hours. It is a diagnosis of exclusion made only when other neurological, otological, infectious, traumatic, and neoplastic causes of facial paralysis have been reasonably ruled out.
Pathophysiology
The leading mechanism is acute inflammation and oedema of the facial nerve within the narrow facial canal in the temporal bone, causing compressive neuropraxia/axon injury and lower motor neurone dysfunction of muscles of facial expression. Proposed triggers include viral reactivation (especially HSV-1, with possible VZV contribution) and immune-mediated inflammation, but causation remains uncertain. Associated branch involvement explains reduced lacrimal/salivary function, taste disturbance (chorda tympani), and hyperacusis (nerve to stapedius).
Risk Factors
- Age 15-45 years
- Diabetes mellitus
- Pregnancy (especially 3rd trimester and first 2 weeks postpartum)
- Immunocompromise
- Obesity
- Hypertension
- Recent upper respiratory tract illness
Clinical Features
Symptoms
- Rapid onset (usually <72 hours) unilateral facial weakness
- Postauricular or ear pain on the affected side
- Dry eye or excessive tearing
- Altered taste
- Dry mouth
- Speech articulation difficulty and drooling
- Cheek or perioral tingling/numb sensation
- Hyperacusis (uncommon)
Signs
- Lower motor neurone pattern facial weakness involving upper and lower face on one side
- Reduced/absent forehead wrinkling and inability to fully close eye
- Flattened nasolabial fold with drooping of mouth corner/eyebrow
- Sagging eyelid or lagophthalmos
- No other focal neurological deficits in typical Bell's palsy
- Atypical signs suggesting alternative diagnosis: forehead sparing, bilateral palsy, gradual progression, vesicular rash, parotid mass, other cranial nerve deficits, hearing loss/tinnitus/otorrhoea, systemic fever
Investigations
Management
Lifestyle Modifications
- Give clear safety-net advice: seek urgent review for eye pain, visual change, worsening neurology, bilateral symptoms, or no improvement trajectory
- Eye protection: frequent lubrication in daytime, lubricating ointment at night, eyelid taping/eye shield during sleep, avoid corneal exposure
- Reassure on natural history while explaining red flags and recurrence possibility
- Advise smoking cessation and optimisation of vascular/metabolic comorbidity (for example diabetes, hypertension)
Pharmacological Treatment
Oral corticosteroid
- Prednisolone 50 mg once daily for 10 days
- Prednisolone 60 mg once daily for 5 days, then reduce by 10 mg daily over 5 days (total 10 days)
Most effective when started within 72 hours of symptom onset (age >=16 years in NICE CKS pathway). Check cautions/contraindications: uncontrolled infection, significant immunosuppression risk, peptic ulcer risk, severe psychiatric history, poorly controlled diabetes, and hypertension; counsel on mood change, dyspepsia, hyperglycaemia. In pregnancy/postpartum, discuss risks/benefits and involve obstetric/specialist teams as needed.
Antiviral therapy
- No antiviral monotherapy for Bell's palsy
Antivirals alone are not recommended; combination antiviral plus steroid has at most small additional benefit and is generally specialist-led (for example if concern for zoster-spectrum disease).
Ocular surface protection
- Hypromellose 0.3% eye drops, 1 drop frequently as required while awake
- Carbomer 0.2% eye gel, typically 1 drop 3-4 times daily
- Paraffin-based lubricating eye ointment at night
Use preservative-free preparations if frequent dosing is needed. Urgent ophthalmology referral if incomplete eye closure with corneal involvement, pain, or reduced vision.
Surgical / Interventional
- No routine acute surgery in primary care
- Refer persistent severe weakness or troublesome sequelae for specialist options (for example facial reanimation procedures, selective botulinum toxin for synkinesis in secondary care)
Complications
- Exposure keratopathy, corneal ulceration, and potential visual loss
- Ectropion
- Synkinesis and hemifacial spasm-like involuntary movements
- Gustatory hyperlacrimation (crocodile tears)
- Persistent facial asymmetry/weakness
- Facial pain and paraesthesia
- Dry mouth
- Hyperacusis
- Psychological morbidity (social distress, anxiety, depression)
Prognosis
Recovery usually begins within 2-3 weeks, and many patients recover fully by 3-4 months. Even without treatment, complete recovery occurs in over 90% with incomplete palsy and about 70% with complete palsy by 6 months; early prednisolone (within 72 hours) improves complete motor recovery rates (about 83% vs 72% without early treatment). Poorer outcomes are associated with complete initial paralysis, delayed recovery, older age, and pregnancy-associated cases; recurrence occurs in about 6.5% (around half within 5 years).
Sources & References
🏥BMJ Best Practice(1)
✅NICE Guidelines(1)
- Bell's palsy[overview]