What is the diagnostic approach for trigeminal neuralgia?

Diagnostic Approach for Trigeminal Neuralgia

The diagnosis of trigeminal neuralgia is primarily clinical, based on the patient's characteristic history of sudden, unilateral, severe, brief, stabbing, recurrent pain in the distribution of one or more branches of the trigeminal nerve, with MRI serving as a supportive diagnostic tool to rule out secondary causes.

Clinical Diagnostic Criteria

• Trigeminal neuralgia (TN) is characterized by recurrent, unilateral brief electric shock-like pains, abrupt in onset and termination, limited to the distribution of one or more branches of the trigeminal nerve 1
• Pain is typically triggered by innocuous stimuli, which is considered an essential diagnostic feature 2
• The most common trigger maneuvers include:
  • Gentle touching of the face (79% of patients) 2
  • Talking (54% of patients) 2
  • Trigger zones are predominantly located in the perioral and nasal region 2
• Nearly all patients (136 of 140 in one study) report provocation of paroxysmal pain by various trigger maneuvers 2

Neurological Examination

• In classical TN, the neurological examination is typically normal 1
• Presence of trigeminal sensory deficits, bilateral involvement of the trigeminal nerve, or abnormal trigeminal reflexes should raise suspicion for symptomatic TN (secondary to structural causes) 3
• The neurological examination in secondary TN should focus on detecting signs of multiple sclerosis (MS) or cerebellopontine tumors 1

Imaging Studies

• MRI is the preferred modality for investigating the trigeminal nerve 4
• High-resolution MRI with contrast of the trigeminal ganglion is recommended prior to any interventional procedures 1
• MRI protocols should include:
  • 3-D heavily T2-weighted MRI sequences 4
  • MR angiography (MRA) 4
  • Pre- and postcontrast imaging 4
  • Thin-cut high-resolution techniques through the course of the trigeminal nerve 4
• MRI can identify structural causes in up to 15% of patients with TN 3
• MRI helps to identify:
  • Neurovascular compression (most common cause in classical TN) 4
  • Multiple sclerosis plaques 5
  • Tumors or other structural lesions 5
  • Trigeminal nerve size (often smaller on the symptomatic side) 4

Advanced Imaging Techniques

• Diffusion tensor imaging (DTI) can detect microstructural tissue changes in symptomatic nerves compared to asymptomatic nerves 4
• MR neurography is an emerging technique useful for characterizing peripheral trigeminal neuropathy 4
• Advanced MRI techniques have detected structural alterations in gray and white matter in patients with trigeminal neuralgia 4

Important Caveats and Pitfalls

• MRI findings of neurovascular contact should be interpreted with caution:
  • Both false-positive and false-negative imaging studies occur 4
  • Congruence rates of imaging and intraoperative findings range from 83% to 100% 4
  • MRI is supportive rather than diagnostic in selecting candidates for microvascular decompression 4
  • Findings should be interpreted in the context of the site of symptoms 4
• CT is complementary for evaluating osseous integrity of the skull base and neural foramina but insufficient to evaluate the full extent of the trigeminal nerve divisions 4
• FDG-PET/CT and ultrasound of the neck are not supported by evidence for the evaluation of isolated trigeminal neuropathy or neuralgia 4

Classification Based on Etiology

• Classical TN: Associated with neurovascular compression of the trigeminal nerve in or around the root entry zone 4
• Type 2 TN: More prolonged pain between the sharp shooting attacks, possibly of more central origin 4
• Secondary TN: Symptomatic of other conditions such as tumors (mostly benign) or multiple sclerosis 4

Differential Diagnosis

• Other trigeminal autonomic cephalgias:
  • SUNCT (Short Unilateral Neuralgiform pain with Conjunctival injection and Tearing) 4
  • SUNA (Short Unilateral Neuralgiform pain with cranial Autonomic features) 4
• Giant cell arteritis (in patients over 50 with temporal pain) 4
• Post-stroke facial pain 4
• Persistent idiopathic facial pain (atypical facial pain) 4

By following this diagnostic approach, clinicians can accurately diagnose trigeminal neuralgia and distinguish it from other facial pain syndromes, leading to appropriate treatment decisions and improved patient outcomes.