What are the steps to diagnose trigeminal neuralgia?

How to Diagnose Trigeminal Neuralgia

The diagnosis of trigeminal neuralgia is made almost entirely based on the patient's history, specifically identifying sudden, unilateral, brief electric shock-like paroxysmal pain in one or more trigeminal nerve branches, triggered by innocuous stimuli, with mandatory pain-free refractory periods between attacks. 1, 2, 3

Essential Clinical Features to Elicit

Pain Characteristics (Pathognomonic Features)

• Paroxysmal attacks lasting seconds to minutes (not continuous pain) with mandatory refractory periods between attacks 4, 1
• Electric shock-like, lancinating, stabbing quality 1, 5
• Unilateral distribution following V2 (maxillary) and/or V3 (mandibular) branches most commonly 1, 6
• Triggered by innocuous stimuli in virtually all patients (97% in systematic studies): gentle touching of the face (79%), talking (54%), brushing teeth, shaving, eating, cold exposure 7, 8
• Trigger zones predominantly located in perioral and nasal regions 7

Red Flags Requiring Urgent Imaging

• Continuous pain between attacks suggests Type 2 trigeminal neuralgia or secondary causes 4
• Sensory deficits in trigeminal distribution mandate urgent imaging to exclude tumors, multiple sclerosis, or other structural lesions 4, 6
• Bilateral symptoms are atypical and warrant expanded differential diagnosis 6
• Autonomic features (tearing, conjunctival injection, rhinorrhea) indicate trigeminal autonomic cephalgias (SUNCT/SUNA), not true trigeminal neuralgia 4, 1

Neurological Examination

In classical trigeminal neuralgia, the neurological examination is typically normal. 2

• Test for sensory changes in trigeminal distribution (light touch, pinprick) 6
• Identify trigger points by gentle palpation of perioral and nasal regions 6, 7
• Assess for motor weakness in muscles of mastication (rare, suggests secondary cause) 9
• Look for signs of multiple sclerosis (optic neuritis, ataxia, spasticity) if secondary trigeminal neuralgia suspected 2

Mandatory Imaging

MRI with high-resolution thin-cut sequences through the entire course of the trigeminal nerve is recommended in all suspected cases prior to any interventional procedures. 1, 6, 2

Specific MRI Protocol

• 3D heavily T2-weighted sequences combined with MRA to characterize neurovascular compression (83-100% congruence with surgical findings) 9, 1, 6
• Pre- and post-contrast imaging provides the best opportunity to identify secondary causes (tumors, multiple sclerosis plaques) 9
• Thin-cut high-resolution techniques covering brainstem to peripheral branches 9, 6
• Include pituitary fossa views if SUNCT/SUNA suspected based on autonomic features 4

Imaging Findings

• Neurovascular compression of the trigeminal nerve root entry zone in classical trigeminal neuralgia 9, 1
• Trigeminal nerve size is smaller on the symptomatic side compared to contralateral side 9, 6
• Demyelinating plaques in brainstem or trigeminal pathway suggest multiple sclerosis as secondary cause 9, 1
• Tumors (schwannomas, meningiomas, metastases) along trigeminal nerve course 9, 8

Critical Caveat

MRI findings of neurovascular contact should be interpreted in the context of clinical symptoms, as both false-positive and false-negative imaging results occur; MRI is supportive rather than diagnostic. 9, 6

Differential Diagnoses to Exclude

Trigeminal Autonomic Cephalgias (SUNCT/SUNA)

• Up to 200 attacks daily with no refractory period between attacks 4, 1
• Prominent autonomic symptoms: tearing, conjunctival injection, rhinorrhea, nasal blockage 4, 1
• Pain distribution mainly in V1 and V2 divisions 4

Post-Herpetic Neuralgia

• Continuous burning pain (not paroxysmal) at site of previous herpes zoster eruption 4, 6
• Allodynia and hyperalgesia in affected dermatome 4, 6
• Clear history of shingles rash 4

Glossopharyngeal Neuralgia

• Pain in deep ear, back of tongue, tonsils, or neck (not V2/V3 distribution) 4, 1
• Triggered by swallowing or coughing 4, 1
• May be associated with syncope 4, 1

Atypical Odontalgia

• Continuous aching pain localized to tooth or tooth-bearing area 4
• Requires intraoral X-rays to rule out dental pathology 4

Giant Cell Arteritis

• Consider in patients over 50 with temporal region pain 1
• Requires urgent evaluation to prevent blindness 1

Diagnostic Algorithm

1. Obtain detailed pain history focusing on paroxysmal vs. continuous nature, duration of individual attacks, presence of refractory periods, and specific triggers 6
2. Perform targeted neurological examination assessing for sensory deficits and trigger zones 6
3. Order MRI head with contrast using 3D heavily T2-weighted sequences and MRA to evaluate for neurovascular compression and exclude secondary causes 1, 6
4. Classify as classical, Type 2, or secondary trigeminal neuralgia based on clinical features and imaging findings 4, 1