Bell’s palsy and other cranial nerve lesions, including trigeminal neuralgia
Description
CN VII - the anatomy generates the localising signs
Branches leave in order; the most proximal deficit sets the level.
| Branch (proximal -> distal) | Function | Lost if lesion is at/above |
|---|---|---|
| Greater petrosal | Lacrimation | Geniculate ganglion |
| Nerve to stapedius | Damps loud sound | Middle ear -> hyperacusis |
| Chorda tympani | Taste anterior 2/3 tongue, submandibular/sublingual secretion | Distal to stapedius -> dysgeusia |
| Motor to face | All muscles of facial expression, platysma, stylohyoid, post. digastric | Any level |
- Bell's palsy - acute idiopathic LMN facial palsy
- Peaks by ~72 h; unilateral; +/- retroauricular/mastoid pain, dysgeusia, hyperacusis, subjective facial numbness (objective V loss is not Bell's)
- Ramsay Hunt (herpes zoster oticus) - VZV reactivation in the geniculate ganglion
- Facial palsy + vesicles in the ear canal/concha/palate + severe otalgia + numb anterior tongue
- Often VIII too -> vertigo, SNHL. Worse prognosis than Bell's; vesicles may appear after the palsy
- Trigeminal neuralgia - paroxysmal, unilateral, electric shock-like pain in a V distribution
- Seconds to 2 minutes, triggered by light touch (chewing, cold wind, shaving, brushing teeth)
- V2 and/or V3 in ~95%; V1 alone rare; refractory period after an attack
- Classic = neurovascular compression (superior cerebellar artery) | Secondary = MS plaque, tumour | Idiopathic
Epidemiology
- Bell's palsy: 20-30/100,000/yr; lifetime risk ~1 in 60; peak 15-45; M=F
- Pregnancy ~3x risk (third trimester and first week postpartum), diabetes, hypertension, obesity, immunocompromise, preceding URTI
- Ramsay Hunt: ~5-10% of acute facial palsies; older, immunosuppressed
- Trigeminal neuralgia: 4-13/100,000/yr; F>M ~1.5-2:1; peak >50
- Onset <40, bilateral, or objective sensory loss -> think MS (TN in 2-5% of MS; MS in ~2-4% of TN)
- Facial palsy is bilateral in <1% - and bilateral is almost never Bell's
Aetiopathogenesis
- Bell's palsy: presumed HSV-1 reactivation -> nerve oedema -> entrapment in the fallopian canal (the narrowest bony segment)
- Ramsay Hunt: VZV reactivation, geniculate ganglion
- Trigeminal neuralgia: focal demyelination of the root entry zone -> ephaptic transmission between touch and pain fibres
- Explains the trigger phenomenon and why sodium-channel blockers work
CN V lesions - by site
- Central (pons, medulla, upper cervical cord) - infarct, tumour, syringobulbia, MS
- Middle cranial fossa - aneurysm, tumour, chronic meningitis
- Trigeminal ganglion / petrous temporal bone - trigeminal schwannoma, meningioma, skull-base fracture
- Total loss across all three divisions localises to the ganglion or sensory root
- Cavernous sinus - V1 only, plus III/IV/VI (aneurysm, tumour, thrombosis)
- V1 is the most vulnerable division - long course through cavernous sinus and superior orbital fissure
CN VII lesions - by site
- UMN - stroke, tumour. Forehead spared (bilateral cortical supply to upper face)
- Pons - with V, VI, and gaze palsy: infarct, MS, tumour, syringobulbia
- CPA / posterior fossa - vestibular schwannoma, meningioma, chronic meningitis (V then VII then VIII)
- Petrous temporal - Bell's (commonest), Ramsay Hunt, cholesteatoma/otitis media, fracture
- Parotid - malignancy (a facial palsy with a parotid lump is cancer until proven otherwise), surgery
- Bilateral LMN facial palsy - GBS, sarcoidosis (Heerfordt), Lyme disease, HIV, bilateral parotid disease, leukaemic infiltration, Melkersson-Rosenthal, mononeuritis multiplex, myasthenia/myopathy (mimic)
Lower cranial nerves
- IX + X together - central: lateral medullary (PICA/vertebral) infarct, tumour, syringobulbia, MND | peripheral: skull-base aneurysm or tumour, chronic meningitis, GBS
- XI - unilateral: neck/skull-base trauma, jugular foramen tumour, basilar invagination, syringomyelia, polio | bilateral: MND, polio, GBS
- XII - UMN (bilateral strokes, MND, skull-base metastases) | LMN unilateral (vertebral artery thrombosis, MND, syringobulbia, posterior fossa or upper neck mass, Chiari) | LMN bilateral (MND, GBS, polio, Chiari)
- Tongue deviates towards the side of an LMN lesion, away from an UMN lesion
Diagnosis
The first question in facial weakness: UMN or LMN?
- Frontalis involved (cannot wrinkle forehead, cannot close eye) = LMN
- Forehead spared, emotional movement preserved, +/- limb signs = UMN
- Bell's phenomenon (eye rolls up on attempted closure) confirms an LMN palsy with incomplete closure
- Grade with House-Brackmann I-VI - VI = complete paralysis, predicts outcome
Features that mean it is NOT Bell's
- Bilateral palsy -> GBS, sarcoid, Lyme, HIV, carcinomatous/lymphomatous meningitis, GPA
- Recurrent ipsilateral -> facial nerve schwannoma or other structural lesion
- Gradual onset over weeks, or no improvement by 3-4 months -> image
- Other cranial nerves, limb signs, or objective V sensory loss
- Vesicles, ear discharge, parotid mass, systemic features, tick exposure
- Sudden complete palsy in a known tumour -> haemorrhage into it
Investigation
- Bell's palsy is clinical - no routine imaging or bloods
- Selective: glucose/HbA1c, Lyme serology if exposure, HIV, ACE/CXR (sarcoid), ANCA
- MRI brain with internal auditory meatus + gadolinium if any red flag above
- Nerve conduction/electroneuronography at 3-14 days if complete palsy - >90% degeneration predicts poor recovery
- Audiometry if VIII symptoms
Trigeminal neuralgia
- Diagnosis is clinical (ICHD-3): paroxysmal, unilateral, shock-like, in V distribution, triggered by innocuous stimuli
- MRI brain with dedicated trigeminal sequences in everyone - identifies neurovascular compression, MS plaque, CPA tumour
- Continuous background ache, sensory deficit, bilateral pain, or age <40 -> secondary cause
- Differential: dental pain, TMJ, giant cell arteritis, cluster headache/SUNCT (autonomic features, longer attacks), post-herpetic neuralgia, glossopharyngeal neuralgia (throat/ear, triggered by swallowing)
Cranial nerve syndromes to recognise
| Syndrome | Nerves | Cause |
|---|---|---|
| Cerebellopontine angle | V (early loss of corneal reflex), VII, VIII, then IX/X + cerebellar | Vestibular schwannoma, meningioma, epidermoid. Bilateral -> NF2 |
| Cavernous sinus | III, IV, V1 (+/- V2), VI | Thrombosis, aneurysm, pituitary apoplexy, tumour |
| Jugular foramen | IX, X, XI (+XII if extending to skull base) | Glomus jugulare, skull-base metastasis (prostate, plasmacytoma), lymphoma, TB, sarcoid, carotid dissection |
| Lateral medullary (Wallenberg) | V (ipsi face pain/temp), IX, X + contralateral body pain/temp, ipsilateral Horner's, ataxia | PICA/vertebral occlusion |
| Multiple cranial nerves | Any combination | Nasopharyngeal carcinoma, chronic/carcinomatous meningitis, TB, sarcoid, GBS (spares sensory), brainstem lesion, Chiari, Paget's, mononeuritis multiplex |
Dissociated trigeminal sensory loss
- Pain lost, touch preserved -> brainstem/upper cervical cord (syringobulbia, foramen magnum tumour, Wallenberg)
- Onion-skin/"balaclava" distribution, spreads towards the nose as the lesion ascends (spinal nucleus of V is somatotopically inverted)
- Touch lost, pain preserved -> pontine principal sensory nucleus (infarct, tumour)
- Single division only (usually V1) -> postganglionic lesion
Management
Bell's palsy
### A. Corticosteroid - the only treatment with clear benefit
- Prednisolone 25 mg BD (or 50-60 mg daily) for 10 days, ideally started within 72 h of onset
- Benefit falls off after 72 h but still offer up to 7 days
- Absolute recovery rate rises from ~65-70% to ~85%
### B. Antiviral - adjunct only
- Valaciclovir 1 g TDS or aciclovir 400 mg 5x daily for 7 days, with the steroid, never instead of it
- Adds <7% to recovery; may reduce synkinesis. Counsel that the benefit is unproven and modest at best
- Reasonable to add for severe/complete palsy (House-Brackmann V-VI)
### C. Eye care - the part that prevents permanent harm
- Lubricating drops hourly by day, ointment + taping or an eye shield at night
- Exposure keratopathy is the main preventable complication - especially with a poor Bell's phenomenon or absent corneal reflex
- Ophthalmology if pain, redness, or visual change; tarsorrhaphy/gold weight if prolonged
### D. If recovery is incomplete
- Facial rehabilitation/neuromuscular retraining (not electrical stimulation)
- Botulinum toxin for synkinesis and contralateral hyperkinesis
- Surgical: nerve graft, cross-facial or masseteric nerve transfer, static slings; decompression rarely and only very early
Ramsay Hunt syndrome
- Antiviral + corticosteroid, started as early as possible - ideally <72 h
- Valaciclovir or famciclovir (aciclovir if IV needed) + prednisolone
- Lower threshold for admission, IV therapy and ENT input; treat even if presenting late
- Audiometry, vestibular assessment, same eye care
- Prevention: shingles vaccination (recombinant zoster vaccine)
Trigeminal neuralgia
### A. First-line medical
- Carbamazepine - the only agent with Class I evidence
- Start 100 mg BD, titrate by 100-200 mg every few days to effect; usual 600-1200 mg/day divided
- Monitor Na (SIADH/hyponatraemia), FBE, LFT; enzyme inducer - check interactions incl. the OCP, DOACs, warfarin
- *HLA-B\15:02 screening before starting in people of Han Chinese, Thai, Malay or South Asian ancestry** - SJS/TEN risk
- Oxcarbazepine - equivalent efficacy, better tolerated, fewer interactions; more hyponatraemia
### B. Add-on / alternatives if intolerant
- Lamotrigine, baclofen, gabapentin, pregabalin, botulinum toxin A
- Acute severe exacerbation with inability to eat or drink: admit for IV fosphenytoin or lidocaine, hydration
### C. Surgical - for medically refractory or intolerant
- Microvascular decompression - first-line surgery if neurovascular conflict on MRI
- Best durable result: ~70-80% pain-free at long-term follow-up; craniotomy, small risk of hearing loss and CSF leak
- Ablative: percutaneous glycerol/radiofrequency/balloon rhizotomy, stereotactic radiosurgery
- Less durable, and cause sensory loss - anaesthesia dolorosa is the feared complication
- In MS-related TN, treat the MS as well; surgical results are less good
Associations
- Bell's palsy - pregnancy, diabetes, hypertension, obesity, preeclampsia, immunosuppression, recent URTI, family history
- Bilateral facial palsy - GBS/Miller Fisher, sarcoidosis (Heerfordt: uveitis + parotitis + fever + facial palsy), Lyme disease, HIV seroconversion, GPA, amyloid, leukaemic infiltration
- Melkersson-Rosenthal - recurrent facial palsy + orofacial oedema + fissured tongue
- Trigeminal neuralgia - multiple sclerosis, CPA tumour, Charcot-Marie-Tooth
- Trigeminal sensory neuropathy - scleroderma, Sjogren's, SLE, MCTD
- Vestibular schwannoma - NF2 if bilateral
- Nasopharyngeal carcinoma - EBV, Southern Chinese ancestry
Natural history & complications
Bell's palsy
- Recovery begins within 3 weeks in ~85% - the single best prognostic sign
- ~70% complete recovery untreated; ~85% with corticosteroid
- Incomplete palsy at presentation -> >94% full recovery; complete palsy -> ~60%
- Poor prognosis: complete palsy, age >60, diabetes, hypertension, severe pain, >90% degeneration on electroneuronography
- Recurrence ~7-8% (ipsilateral recurrence demands imaging)
- Complications: synkinesis (oral-ocular, "crocodile tears" from aberrant lacrimal reinnervation), contracture, hemifacial spasm, exposure keratopathy/corneal ulceration, psychological impact
Ramsay Hunt
- Only ~50% complete recovery, and lower still if treatment delayed
- Residual SNHL, vertigo, post-herpetic neuralgia
Trigeminal neuralgia
- Relapsing-remitting - remissions of months to years early on
- Progressive over time: shorter remissions, higher drug requirement, development of a background ache
- Most eventually escape medical control -> refer for surgical assessment rather than escalating indefinitely
- Weight loss, dehydration, avoidance of eating/hygiene; suicide risk is real - screen for it
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