Assessing Aδ Fiber Function With Lidocaine Using Intraepidermal Electrical Stimulation

The functions of small fibers can be impaired in peripheral neuropathies, and screening tests for clinical use are required. To verify whether intraepidermal stimulation (IES) is useful for assessing the functions of Aδ fibers in the superficial layer, we investigated sensory thresholds and evoked cortical responses in healthy volunteers before and after a transdermal administration of lidocaine. Pain and tactile thresholds were studied using IES and transcutaneous electrical stimulation (TS), respectively, in 10 healthy volunteers before, and 1 hour, 3 hours, and 5 hours after a local anesthesia with lidocaine. Cortical potentials evoked with IES and TS were also studied in 12 healthy volunteers before and 5 hours after the anesthesia. Although the local anesthesia had no effect on the evoked potentials or the tactile threshold for TS, it markedly increased the pain threshold and almost abolished the evoked potentials for IES. These results suggest that IES is a sensitive tool for detecting functional changes of cutaneous Aδ fibers.PerspectiveCompared with other methods of stimulation used to investigate Aδ fiber function, our method is easy to apply and less invasive and can stimulate any site of the body. Therefore, it should be useful as a screening test for patients with neuropathy.