Trigeminal Neuralgia

Symptoms

• Sudden, severe, electric-shock-like or stabbing pain lasting seconds to up to 2 minutes per attack
• Pain in one or more divisions of CN V — V2 (maxillary) and V3 (mandibular) most common; V1 (ophthalmic) alone rare; bilateral in ~3% (think MS)
• Triggered by light touch or innocuous stimuli to the face: shaving, brushing teeth, eating, drinking, talking, cold air, makeup application, kissing
• Trigger zones often along nasolabial fold, lip, gum, cheek
• Refractory period after attack (cannot be triggered immediately)
• Multiple attacks per day or per minute during flares; can have weeks-months of remission
• Pain-free between attacks (vs. atypical facial pain or postherpetic neuralgia)
• Patients may lose weight (afraid to eat), become depressed, develop suicidal ideation

Signs / physical exam

• Normal neurologic examination in classical TN
• Sensory loss in CN V territory, weakness of muscles of mastication, hearing loss, or other cranial nerve findings = RED FLAG for secondary cause (tumor, MS)
• Trigger zones can be elicited but should be done sparingly (severe pain)

Classic findings

Paroxysmal, unilateral, electric-shock-like facial pain triggered by light touch with normal neurologic exam.

Diagnostic criteria

ICHD-3: (A) recurrent paroxysms of unilateral facial pain in CN V distribution lasting fraction of a second to 2 minutes; (B) severe intensity; (C) electric-shock-like, shooting, stabbing, or sharp in quality; (D) precipitated by innocuous stimuli; (E) not better explained by another ICHD-3 diagnosis. Classical (vascular compression on imaging), secondary (identifiable cause like MS or tumor), or idiopathic.

Labs

• Baseline labs prior to carbamazepine: CBC, BMP (sodium), LFTs
• HLA-B*15:02 in patients of Asian descent before starting carbamazepine (severe cutaneous reactions; Stevens-Johnson/TEN)

Imaging

• MRI brain with thin-slice imaging of the trigeminal nerve and brainstem (FIESTA/CISS sequences) — recommended for ALL patients with new TN to evaluate for neurovascular compression, MS plaques, tumors, vascular malformations
• MR angiography may demonstrate the offending vessel
• Reassuring if classical compression visualized in symptomatic patient; alarming if MS lesion, mass, or vascular malformation

First-line

• Carbamazepine — first-line drug; start 100-200 mg BID, titrate slowly to 600-1200 mg/day in divided doses; monitor for SIADH (hyponatremia), leukopenia, aplastic anemia, Stevens-Johnson syndrome (test HLA-B*15:02 in Asian patients); check baseline and periodic CBC, BMP, LFTs
• Oxcarbazepine — better tolerated alternative; start 150-300 mg BID, titrate to 600-1800 mg/day; lower risk of severe rash but still risk of hyponatremia
• If pain controlled and stable, attempt taper after 6-12 weeks pain-free; many patients have recurrent flares requiring chronic therapy
• Patient education about triggers and pain diary

Second-line / adjunct

• Add-on or alternative medications when carbamazepine/oxcarbazepine fail or are not tolerated:
• Lamotrigine (slow titration to avoid rash), baclofen, gabapentin, pregabalin, phenytoin, topiramate, valproate
• Acute flare management: IV fosphenytoin or lidocaine infusion in refractory severe pain (specialty setting)
• Surgical interventions for medically refractory TN:
• • Microvascular decompression (Jannetta procedure) — preferred in younger, healthier patients with documented neurovascular compression; 80-90% initial pain relief, ~70% durable at 10 years; risks include hearing loss, facial weakness, CSF leak, stroke (low)
• • Percutaneous procedures (glycerol rhizotomy, radiofrequency thermocoagulation, balloon compression of Gasserian ganglion) — for older or higher-risk patients; high initial success but more recurrence and risk of facial numbness (anesthesia dolorosa)
• • Stereotactic radiosurgery (Gamma Knife) — non-invasive; delayed onset of relief (weeks to months); recurrence common over years
• Treat underlying cause in secondary TN (MS — disease-modifying therapy; tumor — resection)