Evoked potentials in trigeminal neuralgia.

Trigeminal evoked potentials and sensory thresholds in response to maxillary gum stimulation were obtained in patients with a complaint of unilateral face pain. The patients and the volunteer, normal control groups had undergone no prior surgical or other procedures involving cranial or cervical structures. For statistical purposes, patient data were analyzed with respect to the diagnostic classification of classical trigeminal neuralgia, atypical trigeminal neuralgia, or other face pain states in which the pain extended beyond the trigeminal nerve distribution. Latencies of trigeminal evoked potentials on the affected side were significantly increased (compared to normal control group responses) in patients with classical but not in those with atypical trigeminal neuralgia nor other face pain syndromes. All three patient groups had statistically significant threshold elevations on the affected side compared to the unaffected side. A high level of significance for this test was obtained for the classical trigeminal neuralgia group. Ratings for patients based upon the preoperative electrophysiological findings were highly correlated with long term results of microvascular decompression of the 5th nerve root for classical, but not for atypical trigeminal neuralgia patients. These results support the view that atypical and classical trigeminal neuralgia symptom complexes are caused by different types of physiological dysfunction and that classical trigeminal neuralgia is associated with compression of the trigeminal nerve root. It was suggested that the rating system may be a useful, objective, clinical adjunct in evaluating patients with classical trigeminal neuralgia.