Trigeminal laser-evoked potentials: a neurophysiological tool to detect post-surgical outcome in trigeminovascular contact neuralgia.

Abstract

The aim of this study was to explore the nociceptive system of patients affected by trigeminal neuralgia (TN) secondary to documented vascular contact who underwent microvascular decompression. For that purpose, we used the classical trigeminal reflexes and the trigeminal laser-evoked potentials (tLEPs) before and after surgery, in order to verify any possible change after decompression and determine if there was any correlation between the neurophysiological parameters and the clinical outcome. Eleven patients affected by TN caused by trigeminovascular contact and 10 age-matched controls underwent conventional trigeminal reflexes (bilateral Blink Reflex/BR and Masseter Inhibitory Reflex stimulating infraorbital and mental nerves/MIR V2 and V3) and tLEPs. Patients repeated neurophysiological tests one week after surgery. Short-latency BR and MIR were normal in all patients before surgery and there was no statistical difference before and after surgery. Conversely, in patients before surgery, tLEPs' amplitudes were significantly lower in the affected than in the healthy side (p = 0.017 for V2 and 0.037 for V3 branches). After surgery, on the affected side, tLEP amplitude increased and the pre/post-operative difference was significant (p = 0.017 for V2 and 0.028 for V3 divisions). Nine patients referred satisfactory pain relief and the favourable clinical outcome correlated with the neurophysiological recovery. This study demonstrates that TN caused by trigeminovascular compression may be related to Aδ fibres impairment, and tLEPs are more sensitive than conventional trigeminal reflexes to reveal small fibre dysfunction and to monitor the post-surgical outcome in these patients.