Trigeminal Neuralgia

Definition and classification (ICHD-3). Recurrent unilateral, brief, electric shock-like facial pain, abrupt in onset and termination, confined to one or more divisions of the trigeminal nerve and triggered by innocuous stimuli. Three categories: classical (neurovascular compression, usually by the superior cerebellar artery) in 80–90%; secondary (multiple sclerosis, cerebellopontine angle tumour, skull-base lesion, stroke); and idiopathic.

Clinical features. Paroxysms lasting from a fraction of a second to 2 minutes, affecting V2 and V3 most often and V1 least, right more than left, and almost never crossing the midline. Trigger zones around the nasolabial fold and chin — pain provoked by chewing, talking, brushing the teeth, shaving, washing the face or cold wind. There is a refractory period after an attack, and remissions may last months. Some patients have superimposed continuous background pain (“type 2”).

Red flags suggesting secondary trigeminal neuralgia. Age below 40, bilateral pain, sensory loss in the trigeminal territory, an absent corneal reflex, other cranial nerve palsies, deafness, and failure to respond to carbamazepine. These mandate detailed imaging.

Investigations and differential diagnosis. MRI brain with dedicated high-resolution trigeminal sequences (3D FIESTA/CISS with MR angiography) should be performed in all patients to demonstrate neurovascular compression and exclude a secondary cause; trigeminal reflex (blink reflex) testing is an alternative where MRI is unavailable. Differentials: dental pain, temporomandibular joint dysfunction, giant cell arteritis, post-herpetic neuralgia, cluster headache, glossopharyngeal neuralgia and sinusitis.

Medical management. Carbamazepine is the drug of choice (Level A evidence) — start 100 mg twice daily and titrate to 600–1200 mg/day; 70–80% obtain initial relief. Oxcarbazepine (Level B) is equally effective with better tolerability and fewer drug interactions. Second-line and add-on agents: lamotrigine, baclofen, gabapentin and pregabalin. Note that more than half of initial responders lose their response over 5–10 years.

Geriatric precautions and surgical options. Carbamazepine in older adults causes hyponatraemia (SIADH), ataxia, falls, drowsiness, diplopia, bradycardia and AV block, leucopenia and aplastic anaemia, and rash including Stevens–Johnson syndrome (test HLA-B*1502 in Asian patients); it is a potent CYP450 inducer, reducing levels of warfarin, DOACs, statins and other antiepileptics — monitor sodium, full blood count and liver function. For drug-refractory pain: microvascular decompression gives the best long-term relief (about 70–80% pain-free at 10 years) but needs posterior fossa craniotomy, so frailty must be assessed; percutaneous procedures (radiofrequency thermocoagulation, balloon compression, glycerol rhizolysis) and Gamma Knife stereotactic radiosurgery are preferred in frail or high-risk elderly patients.

Botulinum toxin type A for refractory trigeminal neuralgia. An updated systematic review with meta-analysis (Clin J Pain, 2024) and a comprehensive review of 35 studies (Toxins, 2024) confirm that subcutaneous or submucosal BTX-A significantly reduces VAS pain scores and attack frequency in patients refractory to, or intolerant of, medical and surgical therapy, with transient facial asymmetry as the main adverse effect. A 2026 umbrella review positions BTX-A as an adjunctive third-line option for focal peripheral neuropathic pain — a useful, low-risk choice in frail older patients unsuitable for craniotomy.