What is Trigeminal Neuralgia?
Trigeminal neuralgia is a chronic neuropathic pain condition characterized by sudden, unilateral, severe, brief stabbing recurrent episodes of electric shock-like pain in the distribution of one or more branches of the trigeminal nerve. 1, 2
Clinical Presentation
The hallmark feature is paroxysmal attacks lasting seconds to minutes with mandatory refractory periods between attacks—not continuous pain. 1 The pain is:
- Unilateral and follows the distribution of one or more trigeminal nerve branches, most commonly affecting the second (maxillary) and third (mandibular) divisions 3
- Electric shock-like, lancinating, or stabbing in quality 4, 5
- Triggered by seemingly benign stimuli such as talking, chewing, light touch, or even a breeze across small "trigger zones" on the face 4, 6
- Brief in duration (seconds to minutes per attack) with pain-free intervals between episodes 1, 3
Facial spasms may occur during intense flare-ups, which is why the condition is also known as "tic douloureux" (painful twitch). 4, 6
Pathophysiology
The central underlying mechanism is demyelination of primary sensory trigeminal afferents in the root entry zone, which leads to generation of ectopic impulses and ephaptic crosstalk (abnormal cross-communication between nerve fibers). 5
Carbamazepine works by reducing polysynaptic responses and blocking post-tetanic potentiation, greatly reducing or abolishing pain induced by trigeminal nerve stimulation. 7
Classification
Trigeminal neuralgia is divided into three types based on etiology: 1, 2
- Classical TN: Caused by neurovascular compression with morphological changes at the trigeminal root entry zone (approximately 50% of cases show such compression on imaging) 1, 5
- Secondary TN: Caused by an identifiable underlying condition such as multiple sclerosis, tumors, or other structural lesions affecting the trigeminal nerve 1, 2
- Idiopathic TN: No identifiable cause on imaging or clinical evaluation 4
Type 2 TN presents with prolonged continuous pain between the characteristic sharp shooting attacks and may originate from more central mechanisms rather than peripheral neurovascular compression. 1
Epidemiology
- Average age of onset is 50 to 60 years, with incidence increasing with age 4
- The condition has a profound effect on quality of life, with fear and depression commonly developing if pain is severe 3, 8
Diagnostic Evaluation
Examination findings are typically normal between painful episodes. 4 The diagnosis is made based on clinical history focusing on: 3
- Pain characteristics (paroxysmal vs. continuous)
- Distribution along trigeminal nerve branches
- Presence of trigger factors
- Duration of individual attacks
- Refractory periods between attacks
MRI with high-resolution thin-cut sequences through the trigeminal nerve course is recommended for all patients with suspected TN to evaluate for neurovascular compression and exclude secondary causes such as multiple sclerosis or tumors. 1, 3 The imaging should include 3D heavily T2-weighted sequences combined with MRA to characterize potential vascular compression. 3
The presence of continuous pain should prompt MRI evaluation to rule out secondary causes, as this is not typical of classical TN. 1
Key Diagnostic Pitfalls
Trigeminal neuralgia does not typically cause visible inflammation or swelling, primarily manifesting as a pain syndrome without autonomic features in its classical form. 1
Important differential diagnoses include:
- Trigeminal autonomic cephalgias (SUNCT/SUNA): Present with both pain AND autonomic features like tearing, conjunctival injection, rhinorrhea, with up to 200 attacks daily and no refractory period 1, 2
- Post-herpetic neuralgia: Continuous burning pain at the site of previous herpes zoster with allodynia, not paroxysmal attacks 2, 3
- Glossopharyngeal neuralgia: Pain in deep ear, back of tongue, tonsils, or neck (not V2/V3 distribution), triggered by swallowing 1
- Dental pathology: Must be excluded by dentists before diagnosing TN, as general practitioners may struggle differentiating TN from toothache 6