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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Bell's palsy = acute idiopathic unilateral LMN facial nerve palsy. Diagnosis of exclusion
- LMN pattern: ENTIRE half of face affected including forehead (cannot raise eyebrow). UMN: forehead SPARED
- Treatment: prednisolone 25 mg BD for 10 days, started within 72 hours of onset
- Eye protection: artificial tears, tape eye shut at night (cannot close eye — risk of corneal exposure)
- Prognosis: ~85% make a full recovery. Incomplete recovery more likely if severe at onset
Overview
Bell's palsy is an acute, idiopathic, unilateral lower motor neurone facial nerve (CN VII) palsy. It is thought to be caused by inflammation and oedema of the nerve within the temporal bone, possibly triggered by viral reactivation (HSV-1 most commonly implicated). It is a diagnosis of exclusion — other causes of facial nerve palsy must be considered (Ramsay Hunt syndrome/VZV, Lyme disease, parotid tumour, cholesteatoma, stroke, cerebellopontine angle tumour, sarcoidosis). The facial nerve also carries taste fibres (anterior two-thirds of tongue) and supplies the stapedius muscle, so taste disturbance and hyperacusis may accompany the palsy.
Epidemiology
Bell's palsy is the most common cause of unilateral facial nerve palsy, accounting for ~70% of cases. Annual incidence is approximately 20–30 per 100,000. Peak incidence is in the 15–45 year age group. Risk factors include pregnancy (especially third trimester and first week postpartum), diabetes, and upper respiratory tract infections. There is no side predilection.
Clinical Features
Symptoms
Sudden onset of unilateral facial weakness — develops over hours (maximal within 72 hours)
Inability to close eye on affected side (orbicularis oculi weakness)
Drooping of mouth corner — drooling, difficulty eating
Loss of taste on anterior two-thirds of tongue (chorda tympani involvement)
Hyperacusis (sounds seem louder on affected side — stapedius weakness)
Post-auricular pain preceding or accompanying the palsy
Vesicles in ear canal or on pinna (NOT Bell palsy — Ramsay Hunt syndrome = VZV)
Signs
LMN facial weakness: ENTIRE half of face including forehead (cannot raise eyebrow, wrinkle forehead)
Bell's phenomenon: on attempted eye closure, eye rolls upward and white sclera is visible
Flattening of nasolabial fold
Unable to puff out cheek or whistle
If forehead is SPARED = UMN pattern = NOT Bell palsy (think stroke)
Investigations
First-line
Clinical diagnosisBell palsy is a clinical diagnosis of exclusion. No routine investigations needed for typical presentation
Second-line
BloodsConsider if atypical: Lyme serology (especially if tick exposure), glucose/HbA1c (diabetes), ESR/ACE (sarcoidosis)
MRI brain and IAMsIf atypical features: bilateral, recurrent, progressive, associated with other cranial nerve palsies — to exclude CPA tumour (acoustic neuroma), brainstem lesion, or parotid tumour
Specialist
Nerve conduction studiesRarely needed — may help predict prognosis if severe (electrophysiology at 2 weeks)
Management
NICE CKS — Bell palsy, 20231
Corticosteroids
- Prednisolone 25 mg BD for 10 days (50 mg total daily), started within 72 hours of onset
- Significantly improves complete recovery rate from ~85% to ~95%
- Less benefit if started after 72 hours, but may still be considered
2
Antivirals
- Aciclovir/valaciclovir may be added in severe cases (House-Brackmann grade V–VI) but evidence for benefit is weak
- If vesicles present (Ramsay Hunt syndrome): treat with aciclovir 800 mg 5 times daily for 7 days + prednisolone
3
Eye protection (critical)
- Artificial tears (hypromellose) frequently during the day
- Eye lubricant ointment (lacri-lube) at night
- Tape eye shut at night to prevent corneal exposure and ulceration
- Urgent ophthalmology referral if eye symptoms: pain, redness, reduced vision
4
Follow-up
- Review at 2–4 weeks — most begin to recover within 3 weeks
- If no improvement by 3 months: refer to ENT/neurology — consider alternative diagnosis
- Physiotherapy/facial exercises may help recovery
Complications
- Incomplete recovery: ~15% have some residual weakness, especially if severe at onset
- Corneal exposure and ulceration: From inability to close eye — requires diligent eye care
- Synkinesis: Aberrant nerve regeneration causing involuntary facial movements (e.g. eye closure when smiling)
- Crocodile tears: Aberrant regeneration of salivary fibres to lacrimal gland — tearing when eating
UKMLA Exam Tips
- 1LMN facial palsy: ENTIRE half of face including forehead. UMN: forehead SPARED (bilateral cortical innervation of forehead)
- 2Forehead spared = UMN = think STROKE, not Bell palsy — urgent assessment
- 3Prednisolone within 72 hours — the key treatment. 25 mg BD for 10 days
- 4Eye protection is critical — corneal ulceration can occur if eye cannot close
- 5Vesicles in ear + facial palsy = Ramsay Hunt syndrome (VZV), not Bell palsy — treat with aciclovir + prednisolone
- 6Bilateral facial palsy: think Lyme disease, GBS, sarcoidosis — NOT Bell palsy
- 7Bell's phenomenon: eye rolls up on attempted closure — demonstrates orbicularis weakness
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