What are the clinical differences and assessment approaches for trigeminal nerve (TN) neuralgia and neuropathy?

Clinical Differences Between Trigeminal Neuralgia and Trigeminal Neuropathy

Trigeminal neuralgia and trigeminal neuropathy are fundamentally different conditions: neuralgia presents with paroxysmal, shock-like pain attacks lasting seconds to minutes with pain-free intervals and no sensory deficits, while neuropathy manifests as constant, unremitting pain with demonstrable sensory or motor deficits such as facial numbness or weakness with mastication. 1, 2

Key Distinguishing Clinical Features

Trigeminal Neuralgia Characteristics

• Pain quality: Brief, lancinating, electric shock-like paroxysms lasting seconds to minutes 3, 4
• Pain pattern: Mandatory refractory periods between attacks with complete pain-free intervals 3
• Triggers: Touch-evoked by light stimulation (washing face, brushing teeth, talking, chewing) 4
• Neurological examination: Normal between attacks—no sensory loss, no motor weakness 5, 6
• Distribution: Follows specific trigeminal divisions (V2 and V3 most common) 1

Trigeminal Neuropathy Characteristics

• Pain quality: Constant, unremitting, burning or aching pain of variable intensity 2
• Pain pattern: Continuous without pain-free intervals, non-triggerable 2
• Neurological deficits: Demonstrable sensory loss (facial numbness, decreased sensation) or motor deficits (weakness with mastication from V3 involvement) 1, 2
• Associated features: May have allodynia and hyperalgesia in affected distribution 3

Type 2 Trigeminal Neuralgia (Overlap Syndrome)

• Presents with both paroxysmal attacks AND continuous background pain between episodes 3
• May represent progressive nerve injury evolving from classical neuralgia 7
• Likely originates from more central mechanisms rather than peripheral neurovascular compression 3

Clinical Assessment Approach

History Taking Priorities

• Pain timing: Document whether pain is paroxysmal (seconds to minutes) versus continuous 3, 2
• Refractory periods: Ask specifically about complete pain-free intervals between attacks—their presence strongly suggests neuralgia over neuropathy 3
• Trigger identification: Test for light touch triggers (cotton wisp to face, air puff)—positive triggers indicate neuralgia 4
• Sensory symptoms: Ask about facial numbness, tingling, or altered sensation—these indicate neuropathy, not classical neuralgia 1, 2

Physical Examination Essentials

• Sensory testing: Use light touch, pinprick, and temperature across all three trigeminal divisions bilaterally—any sensory deficit indicates neuropathy 1, 6
• Motor assessment: Test muscles of mastication (jaw opening/closing, lateral movement)—weakness indicates V3 neuropathy 1
• Corneal reflex: Test bilaterally—asymmetry suggests V1 neuropathy 1
• Trigger point mapping: Gently touch suspected trigger zones with cotton—reproducible pain attacks confirm neuralgia 4

Critical Red Flags Requiring Urgent Imaging

• Any sensory or motor deficit: Mandates immediate MRI to evaluate entire trigeminal nerve course for structural lesions 1, 5
• Continuous pain: Should prompt MRI to exclude multiple sclerosis, tumors, or inflammatory processes 3, 5
• Age under 40: Higher likelihood of secondary causes including multiple sclerosis 5, 8
• Bilateral symptoms: Suggests central pathology requiring brainstem imaging 1

Imaging Strategy

For Suspected Trigeminal Neuralgia (Normal Exam)

• MRI with 3D heavily T2-weighted sequences (FIESTA, DRIVE, or CISS) plus MRA to assess for neurovascular compression at the root entry zone 1, 8
• Imaging congruence with surgical findings ranges 83-100% for neurovascular contact 1
• Include brainstem sequences to exclude multiple sclerosis plaques 1, 5

For Suspected Trigeminal Neuropathy (Abnormal Exam)

• MRI with pre- and post-contrast covering entire trigeminal nerve course from brainstem through peripheral branches 1
• Must image Meckel cave, cavernous sinus, skull base foramina, pterygopalatine fossa, and masticator space 1
• Look for tumors, perineural spread, inflammatory lesions, or vascular malformations 1, 5

Common Diagnostic Pitfalls

False-Positive Neuralgia Diagnosis

• Trigeminal autonomic cephalgias (SUNCT/SUNA) mimic neuralgia but include prominent autonomic features (tearing, conjunctival injection, rhinorrhea) with up to 200 attacks daily and NO refractory period 1, 3
• Glossopharyngeal neuralgia presents identically but affects ear/throat/tongue, not face, and may cause syncope 1, 3

Missing Secondary Causes

• Assuming classical neuralgia without MRI risks missing multiple sclerosis (especially in younger patients), tumors, or vascular lesions 5, 8
• Both false-positive and false-negative MRI findings occur for neurovascular compression—interpret imaging in context of symptom laterality 1

Misclassifying Neuropathy as Neuralgia

• Presence of ANY continuous pain component should raise suspicion for neuropathy or Type 2 neuralgia, not classical neuralgia 3, 2
• Sensory deficits exclude classical neuralgia diagnosis and mandate search for structural pathology 1, 6

Etiological Distinctions

Classical Trigeminal Neuralgia

• Neurovascular compression causing focal demyelination at centrally myelinated root entry zone 5, 4
• Demyelination enables ectopic impulse generation and ephaptic crosstalk between fibers 4

Trigeminal Neuropathy

• Results from lesions anywhere along nerve course: brainstem infarction, tumors (gliomas, lymphomas, metastases, perineural spread), inflammatory conditions (sarcoidosis, meningitis), or peripheral nerve injury 1, 2
• Peripheral trigeminal lesions produce asynchronous abnormal axonal activity causing constant pain and sensory loss 2