Figure 1. New classification and diagnostic grading system for trigeminal neuralgia (TN).

^aTN is typically a unilateral condition. Few patients develop TN on both sides of the face over the course of a disease, e.g., in multiple sclerosis, but they virtually never present with simultaneous bilateral pain. ^bThe pain strictly follows the distribution of the trigeminal nerve branches. It does not extend to the posterior third of the scalp, the posterior part of the external ear, or the angle of the mandible (figure 2). ^cParoxysmal pain is the main complaint, but it may be accompanied by continuous pain. ^dTrigger maneuvers include innocuous mechanical stimuli, facial or oral movements, or complex activities such as shaving or applying make-up. Confined trigger zones and a common combination with brisk muscle contractions (tics) help distinguish triggered TN from allodynia in other conditions of neuropathic pain. Trigger maneuvers may be tested by the examiner. ^eMRI readily identifies major neurologic diseases, such as tumors of the cerebellopontine angle or multiple sclerosis. Other investigations may include the neurophysiologic recording of trigeminal reflexes and trigeminal evoked potentials, which become necessary in patients who cannot undergo MRI. ^fAdvanced MRI techniques are capable of demonstrating neurovascular compression with morphologic changes of the trigeminal nerve root.