Diagnosing Trigeminal Neuralgia
Trigeminal neuralgia is diagnosed primarily through clinical criteria, characterized by sudden, unilateral, severe, brief, stabbing, recurrent episodes of pain in the distribution of one or more branches of the trigeminal nerve, with MRI recommended to evaluate for neurovascular compression or secondary causes. 1
Clinical Diagnostic Criteria
Essential Features:
- Pain characteristics:
- Unilateral facial pain (rarely bilateral)
- Distribution along one or more branches of trigeminal nerve
- Brief, paroxysmal attacks lasting seconds to minutes
- Severe intensity, described as electric shock-like, stabbing, or shooting
- Recurrent episodes throughout the day, may remit for weeks/months 1
Triggering Factors:
- Light touch to specific trigger zones
- Common triggers include:
- Washing face
- Exposure to cold wind
- Eating
- Brushing teeth
- Talking 1
Associated Features:
- Fear or depression due to severe pain
- Light touch-evoked pain
- Rarely sensory changes in affected area 1
Classification
Classical Trigeminal Neuralgia (Type 1):
- Episodic, shock-like pain
- Pain-free intervals between attacks
- Most commonly associated with neurovascular compression 2, 3
Type 2 Trigeminal Neuralgia:
- Includes more prolonged pain between sharp shooting attacks
- Constant background pain
- May have different pathophysiology, possibly more central in origin 1, 4
Diagnostic Imaging
MRI Protocol:
- High-resolution MRI is the imaging method of choice 1
- Should include:
- 3D heavily T2-weighted sequences
- Pre- and post-contrast imaging
- Coverage of entire course of trigeminal nerve
- Thin-cut high-resolution techniques 1
Imaging Findings:
- Neurovascular compression of trigeminal nerve (most common finding)
- Congruence rates between imaging and intraoperative findings range from 83-100% 1
- Trigeminal nerve may appear smaller on the symptomatic side 1
- May reveal secondary causes (tumors, multiple sclerosis, etc.) 1
Differential Diagnosis
Important conditions to distinguish from trigeminal neuralgia:
- Glossopharyngeal neuralgia (pain in ear/back of tongue)
- SUNA/SUNCT (short-lasting unilateral neuralgiform with autonomic symptoms)
- Post-stroke pain
- Persistent idiopathic facial pain
- Giant cell arteritis
- Dental pain 1
Treatment Approach
First-Line Pharmacological Treatment:
- Carbamazepine is the primary drug of choice 1, 5, 6
- Initial dose: 100 mg twice daily
- Gradually increase by up to 200 mg/day as needed
- Maintenance dose: 400-800 mg daily
- Maximum dose: 1200 mg daily 5
- Oxcarbazepine is equally effective with fewer side effects 1
Second-Line Medications:
Surgical Options (when medications fail):
- Microvascular decompression (MVD) - preferred non-ablative procedure
- Ablative procedures:
- Radiofrequency thermocoagulation
- Glycerol rhizotomy
- Balloon compression
- Gamma Knife 1
Important Clinical Considerations
- Early neurosurgical consultation is recommended when medications fail 7
- Regular attempts to reduce medication dose should be made every 3 months 5
- Patients with Type 2 TN may have less favorable surgical outcomes than those with classic TN 4
- MRI findings should be interpreted in context with symptoms, as both false positives and negatives can occur 1, 7
- Demyelination of primary sensory trigeminal afferents in the root entry zone is the predominant pathophysiological mechanism 3
Common Pitfalls to Avoid
- Misdiagnosis as dental pain, leading to unnecessary dental procedures
- Failure to obtain MRI to rule out secondary causes
- Inadequate medication dosing before declaring treatment failure
- Delaying surgical consultation when medications are ineffective
- Treating as simple facial pain with analgesics (trigeminal neuralgia does not respond to simple analgesics) 5, 8