S64 Neurophysiological data supporting a peripheral mechanism for trigeminal neuralgia

Abstract

Plenty of neurophysiological, neuroimaging and histological data have definitely established that typical trigeminal neuralgia (TN) follows demyelination of primary afferents near the root entry zone. Another phenotype of trigeminal neuralgia, which is characterized by the presence of concomitant continuous pain in the same territory of the typical paroxysmal pain, poses more problems, because the pathophysiology is unknown and these patients tend to respond less well to pharmacological and surgical treatments. We are doing a prospective, neurophysiological and neuroimaging study in 60 patients (40 with typical TN and 20 with concomitant continuous pain), who undergo neurophysiological recordings of trigeminal reflexes, A-delta related laser evoked potentials (A-LEP), C-related laser evoked potentials (C-LEP), and a volumetric MRI study of the volume of the trigeminal root. In all patients, we measure the asymmetry between affected and contralateral side. In all patients, regardless of the phenotype, all the measures are significantly asymmetrical. Between the two phenotypes, the only statistically significant difference—so far—has been reached by C-LEPs, which are smaller in patients with concomitant continuous pain. This finding may be due to axonal loss of unmyelinated fibres and continuous pain to postganglionic lesion causing anatomical denervation of second-order neurons.