Trigeminal neuralgia

Overview

•Electric shock-like pain - sudden, severe, unilateral, stabbing/lancinating; described as 'like an electric shock'

•Paroxysmal - attacks last seconds to two minutes, then resolve completely

•Unilateral - V2 (maxillary) and V3 (mandibular) most commonly affected; isolated V1 is uncommon

•Trigger factors - light touch, eating, talking, brushing teeth, shaving, cold wind

•Pain-free intervals - patient entirely well between attacks

•Normal neurological examination in classical trigeminal neuralgia - any sensory deficit or cranial nerve sign suggests a secondary cause

⚠️

Bilateral trigeminal neuralgia should always prompt consideration of multiple sclerosis - classical idiopathic trigeminal neuralgia is almost invariably unilateral. TN is 20 times more common in MS patients.

Investigations

•MRI brain with gadolinium - to exclude secondary causes (MS plaques, tumour, AVM, vascular compression); recommended in all new diagnoses

•Bloods before starting *carbamazepine**** - FBC, LFTs, U&Es; HLA-B*1502 genotyping in Han Chinese or Thai patients (Stevens-Johnson syndrome risk)

📌

A normal MRI does not exclude classical trigeminal neuralgia - the diagnosis remains clinical.

Management

🥇 First-line

•carbamazepine (sodium channel blocker) - start 100-200 mg twice daily, titrate to 200 mg three to four times daily; reduce and withdraw during remission periods

🥈 Second-line

•oxcarbazepine - similar mechanism, better tolerated, lower drug interaction risk; initiated with specialist guidance

•Adjuncts (specialist): lamotrigine or baclofen (GABA-B agonist) - baclofen particularly relevant in MS-related trigeminal neuralgia

•Third-line (surgical): refer to neurosurgery for refractory pain or medication intolerance

•Microvascular decompression (MVD) - most durable outcome; for younger, fit patients with imaging-confirmed neurovascular contact

•Stereotactic radiosurgery (Gamma Knife) - less invasive; delayed onset of effect (weeks to months)

•Percutaneous procedures (balloon compression, glycerol injection, radiofrequency thermocoagulation) - risk of facial numbness

🎯

First-line for trigeminal neuralgia is carbamazepine - NOT pregabalin, amitriptyline, or duloxetine, which are used in other neuropathic pain conditions. Carbamazepine specifically targets ectopic sodium-channel-driven discharge.

Follow-up and monitoring

•Review response to carbamazepine at 2-4 weeks after initiation or dose change

•Monitor FBC, LFTs, U&Es periodically - risks include hyponatraemia (SIADH), agranulocytosis, hepatotoxicity

•Refer to neurology if: pain severely limiting; carbamazepine contraindicated, ineffective, or not tolerated; atypical features; secondary cause suspected