Evaluation of nociceptive Aδ- and C-fiber dysfunction with lidocaine using intraepidermal electrical stimulation

• Nociceptive Aδ and C fibers in the epidermis are activated selectively by intraepidermal electrical stimulation (IES) without a sophisticated technique or expensive equipment.
• IES could demonstrate differential effects of transdermal lidocaine on nociceptive Aδ and C fibers, and elucidated the pathophysiology of an experimental model of small-fiber neuropathy (SFN).
• IES may have potential for a clinical tool to elucidate the pathophysiology of patients with SFN.

ObjectiveTo investigate whether intraepidermal electrical stimulation (IES) can evaluate nociceptive Aδ- and C-fiber dysfunctions of an experimental model of small-fiber neuropathy (SFN) with transdermal lidocaine.MethodsLidocaine tape or placebo was applied to the dorsum of the feet in 14 healthy subjects. Reaction time (RT), sensory threshold, and evoked potentials (EPs) were measured using IES before, and 30 and 60 min after lidocaine/placebo application.ResultsAll subjects felt pricking sensations following Aδ-fiber stimulation, and light painful sensations such as pricking, tingling, or burning following C-fiber stimulation using IES. RT was divided bimodally between Aδ- and C-fiber stimulations. At 30 min, lidocaine increased the sensory threshold and decreased the amplitude of EPs in both fiber stimulations. At 60 min, lidocaine’s effects were greater for C fibers than for Aδ fibers. The sensory threshold and amplitude of EPs were unchanged among placebo sessions.ConclusionsIES demonstrated differential effects of transdermal lidocaine on nociceptive Aδ and C fibers, and elucidated the pathophysiology of the experimental model of SFN.SignificanceIES has advantages in terms of cost, convenience, and invasiveness. It may have potential for a clinical tool to elucidate the pathophysiology of patients with SFN, including the differences between Aδ and C fibers.