Assessing the modulation of cutaneous sensory fiber excitability using a fast perception threshold tracking technique

Introduction: Topical application of lidocaine-and-prilocaine (LP) cream attenuates the functionality of small cutaneous nerve fibers. The aim of this human study was to measure the underlying excitability modulation of small cutaneous nerve fibers using a novel and fast perception threshold tracking (PTT) technique. Methods: Small sensory fibers were selectively blocked by 120-minute topical application of LP and confirmed by quantitative sensory testing. Excitability changes of small (activated by a specially designed pin electrode) and large (patch electrode) nerve fibers were assessed as the strength–duration relation and threshold electrotonus. Results: The excitability assessed by the strength–duration relation and threshold electrotonus was significantly modulated for the small afferents (P < 0.05, Wilcoxon's test) but not the large afferents. Discussion: This novel PTT technique was able to assess inhibition of membrane properties of small cutaneous fibers, suggesting the usefulness of the technique as a diagnostic method for assessing impairment of small fibers, as seen in many types of polyneuropathies. Muscle Nerve, 2019.