Trigeminal neuropathic pain.

Typical trigeminal neuralgia is characterized by episodic, unilateral, lancinating, triggerable, often shock-like facial pains, and pain-free intervals. Trigeminal neuropathic pain could be defined as constant unilateral facial pain of variable intensity, is non-triggerable, and unremitting. Atypical trigeminal neuralgia is an overlap syndrome with both episodic and constant pain. Patients with clear pathology of the trigeminal system often have sensory loss and atypical pains. The leading theory of causation of typical trigeminal neuralgia points to minimal compression and demyelination at the root entry zone (REZ) of the trigeminal nerve. In the experience of many neurosurgeons, atypical pains result from lesions or injuries of the trigeminal nerve root distal to the REZ. In a review of 122 patients, distal trigeminal pathology correlated with a clinical syndrome of trigeminal neuropathic pain. An hypothesis is presented that peripheral lesions of the trigeminal nerve behave as do other peripheral nerve lesions in that they are associated with sensory loss, deafferentiation and non "tic-like" pains. This may be due to the asynchronous spatial temporal dispersion of abnormal centrally-propagating axonal activity in nociceptive and non-nociceptive fibers from the region of pathology. This is opposed to the putative synchronous multifiber volleys which may emanate from the proximal trigeminal REZ in patients with typical trigeminal neuralgia. It appears that classical trigeminal neuralgia may be an exception to the rule that nerve injuries typically produce symptoms like constant pain and allodynia. Trigeminal neuropathic pain is, in some ways, a more general syndrome in that it is a painful nerve injury of the distal trigeminal nerve.(ABSTRACT TRUNCATED AT 250 WORDS)