What is the initial workup for a patient presenting with symptoms of trigeminal neuralgia?

Workup for Trigeminal Neuralgia

MRI with contrast of the head, including high-resolution sequences of the trigeminal nerve, is the cornerstone of diagnostic workup for trigeminal neuralgia to identify potential causes such as neurovascular compression, tumors, or demyelinating disease. 1, 2

Clinical Diagnostic Criteria

• Diagnosis is primarily based on characteristic clinical presentation: unilateral, brief electric shock-like pains, abrupt in onset and termination, limited to the distribution of one or more branches of the trigeminal nerve, and triggered by innocuous stimuli 3
• Pain is typically paroxysmal, lasting seconds to minutes, with sharp, shooting, electric shock-like quality 1
• Identify trigger zones - small areas where minimal stimulation may precipitate a painful episode (e.g., light touch, washing, cold wind, eating, brushing teeth) 1, 4
• Assess for facial spasms which may occur during intense flare-ups 4
• Evaluate for sensory changes, which are rare in classic trigeminal neuralgia but may indicate secondary causes 5

Imaging Studies

• High-resolution MRI with contrast of the trigeminal ganglion is the preferred imaging modality 1, 2
• Imaging protocol should include:
  • 3-D heavily T2-weighted MRI sequences 1, 2
  • MR angiography (MRA) to assess for vascular compression 1
  • Pre- and postcontrast imaging 1
  • Thin-cut high-resolution techniques through the entire course of the trigeminal nerve 1
• MRI should cover the entire course of the trigeminal nerve from brainstem to peripheral branches 1
• CT is complementary for evaluating osseous integrity of the skull base and neural foramina but is not the primary imaging modality 1

Classification Based on Imaging Findings

• Classical trigeminal neuralgia: Associated with neurovascular compression of the trigeminal nerve root entry zone 2, 6
• Secondary trigeminal neuralgia: Caused by other conditions such as multiple sclerosis, tumors, or space-occupying lesions 2, 4
• Idiopathic trigeminal neuralgia: No identifiable etiology on imaging 4

Advanced Imaging Considerations

• Diffusion tensor imaging (DTI) can detect microstructural tissue changes in symptomatic nerves 2
• MR neurography is an emerging technique useful for characterizing peripheral trigeminal neuropathy 2
• Trigeminal nerve size measurements are often smaller on the symptomatic side in trigeminal neuralgia 1, 2

Differential Diagnosis Assessment

• Rule out other trigeminal autonomic cephalalgias (SUNCT, SUNA) 1, 2
• Consider giant cell arteritis (check ESR, C-reactive protein) 1
• Evaluate for post-stroke pain 1
• Consider persistent idiopathic facial pain 1
• Assess for post-traumatic trigeminal pain or trigeminal neuropathic pain 1

Laboratory Testing

• No specific laboratory tests are required for classical trigeminal neuralgia 4
• In suspected secondary causes, consider:
  • ESR and CRP if giant cell arteritis is suspected 1
  • Additional testing based on suspected underlying etiology 5

Neurological Examination

• Neurological examination is typically normal in classical trigeminal neuralgia 3
• Assess for trigeminal sensory deficits, which increase risk of symptomatic trigeminal neuralgia 5
• Evaluate trigeminal reflexes - abnormal reflexes are associated with increased risk of symptomatic trigeminal neuralgia 5
• Check for bilateral involvement of the trigeminal nerve, which may indicate secondary causes 5

By following this comprehensive diagnostic approach, clinicians can accurately diagnose trigeminal neuralgia and determine whether it is classical, secondary, or idiopathic, which guides appropriate treatment decisions.