1651 EQUIVALENCY OF ELECTRICAL AND MAGNETIC STIMULATION OF POSTERIOR TIBIAL NERVE (PTNS) AS ASSESSED BY EMG PARAMETERS (F-WAVE)

Abstract

INTRODUCTION AND OBJECTIVES: Level one evidence of efficacy supports the use of posterior tibial nerve stimulation (PTNS) in the treatment of patients with overactive bladder. Percutaneous electrical stimulation of the nerve has been the standard approach to PTNS for many years. Magnetic stimulation is an emerging non-invasive alternative method with the advantage of improved patient comfort. The F-wave is a muscle action potential seen only after supramaximal stimulation of a nerve. The F-wave is elicited when the stimulus travels in a retrograde fashion along the motor fibers and reaches the anterior horn cell causing some of the cells to depolarize creating action potentials that travel back down the nerve resulting in a recordable muscle contraction. Our objective was to demonstrate Fwaves with both electrical and magnetic stimulation of posterior tibial nerve. METHODS: Ten healthy volunteers had EMG recording electrodes placed over the abductor hallucis muscle. Magnetic stimulation of the posterior tibial nerve was then carried out using the EMKinetics TranStim device. Electrical stimulation was carried out using a 34 gauge needle connected to the LG-TEC elite stimulator device. EMG recordings were reviewed by an experienced electromyographer to confirm the presence or absence of F-waves. RESULTS: All ten subjects demonstrated F-waves with magnetic nerve stimulation. Nine out of ten subjects demonstrated F-waves with electrical nerve stimulation. The one subject that did not have an F-wave did not have any recordable electrical muscle activity. This is possibly due to inadequate needle positioning or anomalous nerve location. CONCLUSIONS: This pilot study demonstrates electrodiagnostic equivalence of both magnetic and electrical stimulation of the posterior tibial nerve. Demonstration of an F-wave after posterior tibial nerve stimulation implies that all of the nerve fibers of the nerve bundle have been stimulated (supramaximal stimulation). Both magnetic and electrical nerve stimulation result in identical EMG findings confirmed with F-waves.