Trigeminal Neuralgia (TN)
BASICS
- Definition: Chronic, episodic, unilateral facial pain in the distribution of the trigeminal nerve (CN V), often severe, lancinating, and electric-shock-like, lasting seconds to minutes.
- Trigger: Often initiated by mild stimuli (e.g., brushing teeth, cold air).
- Subtypes:
- Classical TN: Due to neurovascular compression
- Idiopathic TN: No identifiable cause on imaging
- Secondary TN: Structural lesions (e.g., MS, tumor, AVM)
EPIDEMIOLOGY
| Parameter | Data |
|---|---|
| Incidence | 4–29 / 100,000/year |
| Peak age | ~55 years |
| Female:Male ratio | 3:2 |
| Pregnancy | Limited drug options due to teratogenicity |
ETIOLOGY & PATHOPHYSIOLOGY
- Neurovascular compression → demyelination of trigeminal root
- Structural lesions: e.g., meningioma, AVM, acoustic neuroma
- MS: TN may be bilateral and occurs at younger ages
- Mechanism: Ectopic impulse generation, cross-excitation of nearby fibers, dysregulated sodium channels
RISK FACTORS
- Multiple sclerosis (20x increased risk)
- Older age
- Female sex
ASSOCIATED CONDITIONS
| Neurologic | Autoimmune/Other |
|---|---|
| MS | Rheumatoid arthritis |
| Acute polyneuropathy | Sjögren syndrome |
| Charcot-Marie-Tooth |
DIAGNOSIS
HISTORY
- Pain: Sudden, intense, unilateral in V2/V3, rarely V1
- Duration: Seconds to 2 minutes, stereotyped attacks
- Triggers: Light touch, chewing, talking, cold air
- Autonomic features: Lacrimation, conjunctival injection, rhinorrhea (may occur)
- Bilateral pain: Suggestive of MS-associated TN
PHYSICAL EXAM
- Normal between attacks
- Stimulation of trigger zones may reproduce pain
- Absence of sensory loss differentiates TN from other neuralgias
DIAGNOSTIC CRITERIA (ICHD-3)
- A. Recurrent unilateral pain in CN V distribution, without radiation
- B. Pain characteristics:
- Lasts 0.1 to 2 minutes
- Severe, electric shock-like, stabbing
- C. Triggered by innocuous stimuli
- D. Not better explained by another diagnosis
DIFFERENTIAL DIAGNOSIS
- Postherpetic neuralgia
- MS or other demyelinating diseases
- Brainstem AVM or tumor
- Cluster headache
- SUNHA
- Giant cell arteritis
- Migraine
INVESTIGATIONS
Imaging
- MRI with/without contrast (trigeminal protocol): Rule out secondary causes; identify vascular compression
- CT: Alternative if MRI contraindicated
- MR angiography/CT angiogram: To visualize vessel-nerve contact
Labs
- CBC, LFTs, renal panel before initiating meds
- HLA-B*1502 screening: Mandatory in Han Chinese before starting carbamazepine/oxcarbazepine
TREATMENT
GENERAL
- Avoid known triggers (cold air, facial touch, brushing teeth)
- First-line: Anticonvulsants
- Interventions reserved for refractory cases
PHARMACOLOGIC MANAGEMENT
| Drug | Dose | Notes |
|---|---|---|
| Carbamazepine (Tegretol) | Start 100–200 mg BID, up to 1600 mg/day | First-line; monitor CBC, LFTs |
| Oxcarbazepine (Trileptal) | Start 150–300 mg BID | Fewer interactions; more hyponatremia |
| Gabapentin | Start 300 mg daily, titrate to 600 mg QID | Monotherapy or adjunct |
| Baclofen | Start 5 mg TID, up to 80 mg/day | Adjunct to anticonvulsants |
| Phenytoin | Used IV for acute rescue | Slower onset; risk of arrhythmia |
| Lamotrigine | Titrate up to 200 mg BID | Add-on; interactions common |
| Botulinum toxin | Local injection | May reduce pain in some patients |
| Pimozide | Rare use | Risk of QT prolongation and EPS |
INTERVENTIONS
Indications for Referral
- Inadequate response to 1st-line therapy
- Structural lesion on imaging
- Complicated TN (e.g., bilateral, associated with MS)
PROCEDURAL OPTIONS
| Procedure | Indication | Outcomes |
|---|---|---|
| Microvascular decompression | Classical TN with confirmed neurovascular compression | 68–88% pain-free at 1–2 yrs |
| Stereotactic radiosurgery (e.g., Gamma Knife) | Refractory TN or unsuitable for open surgery | 24–71% effective at 1–2 yrs |
| Percutaneous rhizotomy/thermocoagulation | Older or poor surgical candidates | Risk: facial numbness |
| Glycerol/radiofrequency ablation | For severe pain needing quick relief | Risk: anesthesia dolorosa |
| Balloon compression of CN V | For patients not suitable for decompression | Moderate efficacy |
| Peripheral nerve blocks | Temporary relief | Often used diagnostically |
COMPLEMENTARY & ALTERNATIVE
- Acupuncture: Some evidence for pain modulation
- Psychosocial support: For chronic pain and QoL impact
ONGOING CARE
| Follow-Up | Labs & Monitoring |
|---|---|
| Every 3–6 months initially | CBC, CMP if on carbamazepine |
| Taper meds after 4–6 weeks pain-free | Reassess remission |
| Consider neurology/pain specialist | Multidisciplinary care beneficial |
PATIENT EDUCATION
PROGNOSIS
| Metric | Value |
|---|---|
| Medication failure rate | 50–60% |
| Radiosurgery relapse | ~50% |
| MVD relapse | ~27% |
| Long-term outlook | Improved with early, specialized multidisciplinary care |
COMPLICATIONS
| Medication | Interventional |
|---|---|
| Sedation, dizziness, hyponatremia, SJS (carbamazepine) | Numbness, paresthesias, anesthesia dolorosa |
| Carbamazepine: aplastic anemia, liver toxicity | MVD: bleeding, stroke, infection |
| Stereotactic radiosurgery: corneal reflex loss | Balloon compression: trigeminal nerve damage |
ICD-10 CODES
| Code | Description |
|---|---|
| G50.0 | Trigeminal neuralgia |
| B02.22 | Postherpetic trigeminal neuralgia |
CLINICAL PEARLS
- TN = "lightning pain" triggered by touch, talking, or cold
- Diagnosis = clinical + MRI
- No sensory loss → favors TN; presence of sensory deficit → think of tumor/MS
- Start carbamazepine or oxcarbazepine
- Microvascular decompression = most durable long-term option
- Consider psychosocial burden → support essential