Bell's Palsy
Summary
Bell's palsy is the most common cause of acute unilateral facial paralysis, characterised by sudden onset lower motor neuron (LMN) weakness affecting one side of the face. It is a diagnosis of exclusion after ruling out identifiable causes. The exact aetiology is unknown but is believed to be related to viral reactivation (particularly HSV-1) causing inflammation and oedema of the facial nerve within the temporal bone. Most patients (70%) make a complete recovery, especially with early corticosteroid treatment initiated within 72 hours.
Key Facts
- Definition: Acute idiopathic unilateral lower motor neuron facial paralysis
- Incidence: 20-30 per 100,000 per year; lifetime risk 1 in 60
- Key Feature: LMN pattern — forehead IS affected (unlike UMN stroke)
- Peak Age: 15-45 years; rare in children <10 years
- Treatment: Prednisolone within 72 hours of onset
- Prognosis: 70% complete recovery without treatment; 85%+ with steroids
Clinical Pearls
"Forehead Test": In Bell's palsy, the forehead IS affected (cannot wrinkle forehead, raise eyebrow). In stroke (UMN lesion), forehead is spared due to bilateral cortical innervation of upper face. This is THE key distinguishing feature.
Vesicles = Ramsay Hunt: If vesicles are visible in the ear canal or on the pinna, this is Ramsay Hunt syndrome (VZV), not Bell's palsy. Consider antivirals in addition to steroids.
Eye Protection is Critical: The inability to close the eye risks corneal exposure, drying, and ulceration. Aggressive eye care (lubricants, taping) is essential — a corneal ulcer is a preventable complication.
Why This Matters Clinically
Bell's palsy is common and can be alarming to patients who often fear stroke. Rapid accurate diagnosis, early steroid treatment, and proper eye care are essential. While prognosis is generally good, incomplete recovery causes significant psychological distress and facial asymmetry.
Incidence & Prevalence
- Incidence: 20-30 per 100,000 per year
- Lifetime Risk: 1 in 60 people
- Peak Age: 15-45 years
- Seasonal: No clear seasonal pattern (though some studies suggest winter peaks)
- Rare in Children: Under 10 years — consider other causes
Demographics
| Factor | Details |
|---|---|
| Age | Peak 15-45 years; can occur any age |
| Sex | Equal male:female |
| Side | Right = Left (unilateral) |
| Bilateral | Very rare (<1%) — consider GBS, Lyme, bilateral Bell's |
| Recurrence | 7-10% lifetime |
Risk Factors
Non-Modifiable:
- Pregnancy (especially third trimester and postpartum)
- Diabetes mellitus (3x risk; worse outcomes)
- Family history (10-14% have affected relative)
- Upper respiratory tract infection (preceding)
Association — NOT Causation:
- Hypertension
- Immunocompromised states
Mechanism
Step 1: Viral Reactivation (Probable)
- HSV-1 reactivation from geniculate ganglion (most likely)
- VZV if Ramsay Hunt syndrome (with vesicles)
Step 2: Nerve Inflammation
- Inflammatory response causes oedema
- Nerve swells within rigid fallopian canal (temporal bone)
Step 3: Compression and Ischaemia
- Swollen nerve compressed against bone
- Microvascular compromise
- Demyelination occurs
Step 4: Conduction Block
- Nerve conduction impaired
- If severe: axonal degeneration (worse prognosis)
- Wallerian degeneration if axons damaged
Anatomical Considerations
Facial Nerve Course:
- Intracranial: From pontomedullary junction
- Internal acoustic meatus: With CN VIII
- Labyrinthine segment: Narrowest part
- Geniculate ganglion: Contains HSV latent
- Tympanic segment: Horizontal through middle ear
- Mastoid segment: Vertical
- Stylomastoid foramen: Exits skull
- Parotid gland: Divides into branches
Motor Branches (Facial Expression):
- Temporal, Zygomatic, Buccal, Mandibular, Cervical
- ("Two Zombies Bit My Cat")
Other Functions:
- Taste (anterior 2/3 tongue — chorda tympani)
- Lacrimation (greater petrosal nerve)
- Stapedius muscle (hyperacusis if affected)
UMN vs LMN Pattern
| Feature | LMN (Bell's Palsy) | UMN (Stroke) |
|---|---|---|
| Forehead | AFFECTED (weak) | SPARED (normal) |
| Eyebrow raise | Weak | Normal |
| Eye closure | Weak | May be weak or normal |
| Lower face | Weak | Weak |
| Cause | Peripheral nerve | Central (brain) |
Symptoms
Typical Presentation:
Atypical Presentations:
Signs
Red Flags
[!CAUTION] Red Flags — Consider alternative diagnosis:
- Forehead sparing (UMN — stroke)
- Vesicles on ear/palate (Ramsay Hunt — needs antivirals)
- Bilateral weakness (GBS, Lyme, sarcoidosis, bilateral Bell's)
- Progressive over weeks (tumour, parotid malignancy)
- No recovery by 3-4 months (refer for MRI)
- Recurrent episodes (investigate for underlying cause)
- Other cranial nerve involvement (brainstem lesion)
- Limb weakness, sensory symptoms (GBS, MS)
Structured Approach
General:
- Observe face at rest for asymmetry
- Complete cranial nerve examination
- Examine ears (vesicles = Ramsay Hunt)
- Check for other neurological signs
Facial Nerve Testing:
- Raise eyebrows (frontalis)
- Close eyes tightly (orbicularis oculi)
- Puff out cheeks
- Show teeth (smile)
- Whistle/purse lips
Special Tests
| Test | Technique | Positive Finding | Significance |
|---|---|---|---|
| Forehead Wrinkling | Ask to raise eyebrows | Cannot wrinkle forehead | Confirms LMN lesion |
| Eye Closure | Close eyes against resistance | Weakness, Bell's phenomenon | LMN lesion |
| Bell's Phenomenon | Attempt eye closure | Eye rolls upward as eyelid fails to close | Positive in LMN lesion |
| Corneal Reflex | Light touch to cornea | Check sensory (V1) and motor (VII) | Should be present in Bell's (motor weak) |
| Ear Examination | Otoscopy | Vesicles | Ramsay Hunt syndrome |
| Taste (Optional) | Test anterior 2/3 tongue | Decreased on affected side | Suggests proximal lesion |
House-Brackmann Grading System
| Grade | Description | Definition |
|---|---|---|
| I | Normal | Normal facial function |
| II | Mild dysfunction | Slight weakness on close inspection; complete eye closure |
| III | Moderate dysfunction | Obvious but not disfiguring weakness; complete eye closure with effort |
| IV | Moderately severe | Obvious disfiguring weakness; incomplete eye closure |
| V | Severe | Barely perceptible motion |
| VI | Total paralysis | No movement |
First-Line (Bedside)
- Clinical diagnosis — no investigations routinely required
- Ear examination (rule out Ramsay Hunt)
- Blood pressure (exclude stroke differential)
- Blood glucose (diabetes worsens prognosis)
Laboratory Tests
| Test | Expected Finding | Purpose |
|---|---|---|
| Usually not required | — | Clinical diagnosis |
| Blood glucose / HbA1c | Elevated if diabetic | Prognostic factor |
| Lyme serology | If endemic area or bilateral | Rule out Lyme disease |
| VZV serology | If clinical diagnosis unclear | Confirm Ramsay Hunt |
Imaging
| Modality | Findings | Indication |
|---|---|---|
| MRI (Contrast) | Nerve enhancement; excludes tumour | If no recovery by 3-4 months; progressive; recurrent |
| CT Head | Excludes stroke (if clinical uncertainty) | Only if UMN pattern suspected |
Diagnostic Criteria
Bell's palsy is a diagnosis of exclusion:
- Acute onset (<72 hours)
- Unilateral LMN facial weakness
- No other identifiable cause
- Forehead affected (rules out UMN/stroke)
Management Algorithm
BELL'S PALSY MANAGEMENT
↓
┌─────────────────────────────────────────────────────┐
│ CORTICOSTEROIDS (START WITHIN 72 HOURS) │
│ │
│ Prednisolone 50mg once daily for 10 days │
│ OR │
│ Prednisolone 60mg/day for 5 days, then taper │
│ │
│ Improves recovery from ~70% to ~85% complete │
└─────────────────────────────────────────────────────┘
↓
┌─────────────────────────────────────────────────────┐
│ ANTIVIRALS — NOT RECOMMENDED FOR BELL'S │
│ │
│ Evidence does NOT support routine antivirals alone │
│ or combined with steroids for Bell's palsy │
│ │
│ ⚠ EXCEPTION: RAMSAY HUNT SYNDROME │
│ If vesicles present: Add Aciclovir 800mg 5x/day │
│ for 7 days (or Valaciclovir) │
└─────────────────────────────────────────────────────┘
↓
┌─────────────────────────────────────────────────────┐
│ EYE CARE (ESSENTIAL) │
│ │
│ CRITICAL to prevent corneal damage: │
│ • Artificial tears every 2 hours during day │
│ • Lubricating eye ointment at night │
│ • Tape eye closed at night if incomplete closure │
│ • Protective glasses/eyepatch during day if needed │
│ • Refer ophthalmology if corneal symptoms develop │
└─────────────────────────────────────────────────────┘
↓
FOLLOW-UP
↓
┌─────────────────────────────────────────────────────┐
│ Review at 2-4 weeks: │
│ • Assess recovery │
│ • Ensure eye care adequate │
│ │
│ No recovery by 3-4 months: │
│ • Refer neurology/ENT │
│ • Consider MRI (exclude tumour) │
│ │
│ Incomplete recovery: │
│ • Facial physiotherapy │
│ • Botox for synkinesis │
│ • Surgical options (rarely needed) │
└─────────────────────────────────────────────────────┘
Acute Treatment
Corticosteroids (Essential):
- Prednisolone 50mg OD for 10 days (no taper needed)
- OR 60mg for 5 days then taper over 5 days
- Start within 72 hours of symptom onset
- NNT = ~9 (one additional complete recovery per 9 treated)
Antivirals (NOT Recommended):
- No benefit shown for Bell's palsy alone
- Only use if Ramsay Hunt syndrome (vesicles present)
Eye Care (Critical):
- Artificial tears (carmellose/hypromellose) every 2 hours
- Lubricating ointment (Lacri-Lube) at night
- Tape eye closed at night if cannot close fully
- Protective glasses if outdoors
- Urgent ophthalmology if red, painful eye (corneal ulcer)
Supportive Care
- Reassurance (most recover fully)
- Advise on eye protection
- Sick note if needed
- Safety netting for red flags
Rehabilitation
If Incomplete Recovery:
- Facial physiotherapy (guided exercises)
- Mirror exercises
- EMG biofeedback therapy
- Botox for synkinesis (unwanted movements)
Surgical Options (Rarely Needed)
- Tarsorrhaphy: Partial closure of eyelids (corneal protection)
- Gold weight implant: Upper eyelid loading (helps closure)
- Facial reanimation surgery: For complete non-recovery
Acute
| Complication | Presentation | Management |
|---|---|---|
| Corneal exposure | Dry, gritty eye | Lubricants, taping |
| Corneal ulcer | Painful red eye, photophobia | Urgent ophthalmology |
Chronic/Recovery-Related
- Synkinesis (15-20%): Abnormal co-movement (e.g., eye closes when smiling) — treat with Botox, physiotherapy
- Crocodile tears: Lacrimation while eating — aberrant regeneration
- Contracture: Fixed facial asymmetry
- Psychological distress: Embarrassment, anxiety, depression
Natural History
Without treatment, ~70% of patients with Bell's palsy achieve complete recovery. With early corticosteroid treatment, this increases to 85-90%. Most improvement occurs within the first 3 weeks, with maximal recovery by 9-12 months.
Outcomes with Treatment
| Variable | Outcome |
|---|---|
| Complete recovery (steroids) | 85-90% |
| Complete recovery (no treatment) | 70% |
| Partial recovery | 10-15% |
| Severe residual weakness | <5% |
| Time to maximal recovery | 9-12 months |
Prognostic Factors
Good Prognosis:
- Younger age
- Early treatment (<72 hours)
- Incomplete paralysis at onset
- Early signs of recovery (within 3 weeks)
- No diabetes
- House-Brackmann Grade I-III
Poor Prognosis:
- Complete paralysis at onset
- Age >60 years
- Diabetes mellitus
- Pregnancy-associated
- No recovery signs by 3-4 months
- House-Brackmann Grade V-VI
- Electroneuronography (ENoG) showing >90% degeneration
Key Guidelines
-
NICE Clinical Knowledge Summary (2019) — Recommends prednisolone within 72 hours; does NOT recommend antivirals for Bell's palsy alone.
-
American Academy of Neurology (2012) — Supports corticosteroids; states antivirals may be offered but benefit uncertain.
Landmark Trials
Scottish Bell's Palsy Study (Sullivan et al., 2007) — NEJM
- 496 patients randomised to prednisolone, aciclovir, both, or neither
- Key finding: Prednisolone improved complete recovery (83% vs 64%); aciclovir no additional benefit
- Clinical Impact: Established prednisolone as standard; ended routine antiviral use
Cochrane Review (Gagyor et al., 2019) — Antivirals
- Meta-analysis of antivirals for Bell's palsy
- Key finding: No significant benefit of antivirals combined with steroids vs steroids alone
- Clinical Impact: Reinforces that antivirals not indicated for Bell's palsy
Evidence Strength
| Intervention | Level | Key Evidence |
|---|---|---|
| Corticosteroids | 1a | Cochrane review, NEJM RCT |
| Antivirals (Bell's palsy) | 1a | Meta-analyses show no benefit |
| Antivirals (Ramsay Hunt) | 2b | Lower quality evidence, but recommended |
| Eye care | 2b | Best practice, observational |
What is Bell's Palsy?
Bell's palsy is a condition that causes sudden weakness of the muscles on one side of your face. It happens when the nerve that controls your facial muscles becomes swollen and stops working properly. The exact cause isn't known, but it's thought to be related to a viral infection.
Why does it matter?
When the facial nerve isn't working, you may not be able to close your eye, smile, or move that side of your face. This can be frightening and embarrassing. The most important thing to know is that most people recover fully, especially with early treatment.
How is it treated?
-
Steroid tablets: Taking prednisolone (a steroid) within the first 72 hours significantly improves your chances of complete recovery. You'll take these for about 10 days.
-
Eye care: This is very important! Because you may not be able to close your eye properly, it can dry out and get damaged. You'll need:
- Eye drops during the day (every 2 hours)
- Eye ointment at night
- Tape the eye closed at night if you can't close it
-
Antiviral tablets: These are NOT usually needed for Bell's palsy (despite what you might read online). They're only given if you have a slightly different condition called Ramsay Hunt syndrome (which causes a rash in your ear).
What to expect
- Most people (7-9 out of 10) make a complete recovery
- You may start to see improvement within 2-3 weeks
- Full recovery can take up to several months
- A small number of people have some lasting weakness or unusual movements
When to seek help
See a doctor urgently if:
- You develop weakness on the OTHER side of your face as well
- You have rash or blisters in your ear (this is a different condition)
- You have weakness in your arms or legs
- Your eye becomes red, painful, or you have vision changes
- There's no improvement after 3-4 months
Primary Guidelines
-
National Institute for Health and Care Excellence. Bell's palsy. Clinical Knowledge Summaries. 2019.
-
Gronseth GS, Paduga R; American Academy of Neurology. Evidence-based guideline update: Steroids and antivirals for Bell palsy: Report of the Guideline Development Subcommittee of the American Academy of Neurology. Neurology. 2012;79(22):2209-2213. PMID: 23136264
Key Trials
-
Sullivan FM, Swan IR, Donnan PT, et al. Early treatment with prednisolone or acyclovir in Bell's palsy. N Engl J Med. 2007;357(16):1598-1607. PMID: 17942873
-
Gagyor I, Madhok VB, Daly F, Sullivan F. Antiviral treatment for Bell's palsy (idiopathic facial paralysis). Cochrane Database Syst Rev. 2019;9:CD001869. PMID: 31486071
Further Resources
- Facial Palsy UK: facialpalsy.org.uk
- NICE CKS: cks.nice.org.uk
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate guidelines and specialists for patient care.