Trigeminal Neuralgia
Severe, paroxysmal, lancinating facial pain in the distribution of one or more divisions of the trigeminal nerve. Attacks last seconds to 2 minutes and are triggered by innocuous stimuli. First-line treatment is carbamazepine. MRI is mandatory to exclude secondary causes.
Key Facts
Paroxysmal, lancinating/electric-shock facial pain in trigeminal nerve distribution (V2/V3 most common); lasts seconds to 2 minutes Triggered by innocuous stimuli: light touch to trigger zones, chewing, talking, brushing teeth, cold wind Incidence: ~12 per 100,000/year; F:M 1.5:1; typically >50 years; if <40 years consider secondary cause (MS) Classical TN (~90%): neurovascular compression (usually superior cerebellar artery) at the root entry zone of CN V Secondary TN: MS (demyelinating plaque in pons — 2-4% of MS patients develop TN), cerebellopontine angle tumour, skull base lesion First-line: carbamazepine 100-1600mg/day (start 100mg BD, titrate; NICE CG150); alternative: oxcarbazepine 300-1800mg/day MRI brain: mandatory to exclude secondary causes; MRA/FIESTA sequence may demonstrate neurovascular compression
Overview
Key Facts
TN causes one of the most severe pains known. Carbamazepine is the first-line treatment and also serves as a diagnostic aid (strong response supports diagnosis). MRI is essential to exclude secondary causes, particularly MS in younger patients.
Epidemiology
Incidence ~12 per 100,000/year. Prevalence ~0.3 per 1,000. F:M 1.5:1. Mean age of onset >50 years. Right side more common than left. Bilateral in <5% (if bilateral, strongly suspect MS).
Aetiology
- Classical TN (~90%): neurovascular compression of the trigeminal nerve root entry zone — most commonly by the superior cerebellar artery; focal demyelination at the compression site
- Secondary TN: MS (2-4%), CPA tumours (meningioma, schwannoma, epidermoid), arteriovenous malformations, skull base lesions
- Idiopathic TN: no demonstrable cause on MRI
Pathophysiology
Neurovascular compression causes focal demyelination of the trigeminal root → ephaptic transmission (cross-talk between adjacent nerve fibres) → paroxysmal discharges triggered by light touch (Aβ fibres activating nociceptive pathways). In MS, demyelinating plaques in the pontine trigeminal pathways produce similar ephaptic transmission.
Clinical Presentation
Pain Characteristics
- Severe, paroxysmal, lancinating/electric-shock pain
- Duration: 1 second to 2 minutes per paroxysm
- Distribution: V2 (maxillary — 35%), V3 (mandibular — 30%), V2+V3 (20%), V1 (ophthalmic — 5%); rarely bilateral (<5%)
- Unilateral and strictly confined to trigeminal territory
- Trigger zones: nasolabial fold, upper lip, gum, cheek
- Triggered by: light touch, talking, chewing, brushing teeth, cold wind, shaving
- Refractory periods: pain-free intervals between paroxysms
Between Attacks
- Completely pain-free (classical TN)
- Some patients develop continuous background aching (TN with concomitant continuous pain)
Red Flags
- Age <40 → consider MS (MRI essential)
- Bilateral → highly suggestive of MS
- Sensory deficit in trigeminal territory → secondary cause (compression/infiltration)
- Associated cranial nerve deficits → CPA lesion
- Poor response to carbamazepine → reconsider diagnosis
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Dental pathology | Related to tooth, continuous pain, dental exam abnormal | Dental assessment, OPG |
| Cluster headache | Periorbital, autonomic features, 15-180 min, restlessness | Clinical |
| Postherpetic neuralgia | History of shingles, continuous burning pain | History, clinical |
| TMJ dysfunction | Jaw pain, clicking, limitation of opening | Clinical, OPG |
| SUNCT/SUNA | Periorbital, autonomic features, very brief attacks | Clinical |
| Glossopharyngeal neuralgia | Throat/ear pain triggered by swallowing | Clinical |
Diagnosis / Investigation
Imaging
- MRI brain: MANDATORY — exclude secondary causes (MS plaques, CPA tumour)
- MRI with FIESTA/CISS sequence: high-resolution imaging of trigeminal root; may demonstrate neurovascular compression
- MRA: identify compressing vessel
Bloods
- FBC, U&Es, LFTs: baseline before starting carbamazepine
- HLA-B*15:02: screen in patients of Han Chinese/South-East Asian descent before carbamazepine (risk of Stevens-Johnson syndrome)
Other
- Response to carbamazepine: strong response supports the diagnosis (has diagnostic as well as therapeutic value)
Management
Pharmacological (NICE CG150)
- First-line: carbamazepine 100mg BD, titrate to 200-400mg BD (max 1600mg/day); effective in ~70-80%; monitor FBC, LFTs, Na⁺ (hyponatraemia)
- Alternative: oxcarbazepine 300-1800mg/day (better tolerated, fewer drug interactions; also causes hyponatraemia)
- Second-line: lamotrigine 200-400mg/day, gabapentin 300-3600mg/day, pregabalin 150-600mg/day, baclofen 40-80mg/day
- Combination therapy: carbamazepine + lamotrigine or baclofen if monotherapy fails
Surgical/Interventional (Refractory)
- Microvascular decompression (MVD): definitive treatment; separates artery from nerve root; ~90% initial pain-free rate; ~70% pain-free at 10 years; general anaesthetic, posterior fossa craniotomy; risk: hearing loss (~1%), CSF leak, stroke (<1%)
- Percutaneous procedures: radiofrequency thermocoagulation, balloon compression, glycerol injection — via foramen ovale; ~90% initial relief but higher recurrence; suitable for elderly/those unfit for MVD
- Stereotactic radiosurgery (Gamma Knife): non-invasive; 60-80% response; delayed onset of effect (weeks-months); can be repeated
Referral Criteria
- Neurology: all TN patients for diagnosis confirmation and imaging
- Neurosurgery: failed ≥2 medications or patient preference for surgery
Prognosis
Natural history: tends to worsen over time with increasing frequency and severity. Carbamazepine effective in ~70-80% initially; efficacy may decline over years. MVD has best long-term outcomes (~70% pain-free at 10 years). Percutaneous procedures: ~90% initial relief but ~50% recurrence at 3-5 years. Gamma Knife: 60-80% response. Without treatment, TN causes profound disability, depression, and significant reduction in quality of life.
Other Relevant Information
Trigeminal Nerve Divisions
| Division | Territory | TN Frequency |
|---|---|---|
| V1 (Ophthalmic) | Forehead, upper eyelid, nose bridge | ~5% |
| V2 (Maxillary) | Cheek, upper lip, upper teeth, nasal cavity | ~35% |
| V3 (Mandibular) | Lower jaw, lower lip, lower teeth, tongue | ~30% |
| V2 + V3 | Combined | ~20% |
Surgical Options Comparison
| Procedure | Pain-Free Rate | Recurrence | Advantage |
|---|---|---|---|
| MVD | ~90% | ~30% at 10 years | Best long-term results |
| RF thermocoagulation | ~90% | ~50% at 3-5 years | Day case, local anaesthetic |
| Gamma Knife | 60-80% | ~50% at 3-5 years | Non-invasive |