Trigeminal Neuralgia
Chapter notes (PDF)PDFSevere, 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 |