2004•Journal of the Peripheral Nervous SystemRequires access
New neurophysiological findings on skin receptors or intradermal nerve endings after repetitive capsaicin application
Irene Aprile, Erik Stålberg, Pietro Caliandro, Costanza Pazzaglia, P. Tonali, M. Foschini, E.E. Trotta, Luca Padua
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Abstract
Background: The standard sensory nerve conduction studies evaluate only large myelinated fibres and its sensitivity may be low in early sensory polyneuropathy where only skin receptors or intradermal nerve endings are involved. During conventional sensory nerve conduction studies through surface electrodes, when we slowly increased the intensity of the stimulus, we occasionally observed a sensory response characterised by a particular morphology with two peaks (double peak potential). Some observations suggested that the first peak was due to stimulation of the nerve fibers and the second peak was due to the activation of the skin receptors or intradermal nerve endings. Objective: The aim of this study is to demonstrate that the second peak is due to activation of the receptors and epidermal nerve fibres. Previously, studies showed that repeated topical applications of capsaicin to human subjects resulted in progressive, almost complete, degeneration of receptors and epidermal nerve fibres. In the present study we report the effects of repeated topical applications of capsaicin to the fingertip of the human subjects on the double peak potential. Materials and Methods: Five‐healthy symptom‐free volunteers participated. Capsaicin cream (0,075%) was applied topically four times daily for 4–5 weeks to the fingertip of digit III (on the distal phalanx). Double peak evaluation and sensory tests were performed before treatment, at intervals during treatment and after capsaicin was discontinued. Results: The second peak obtained using submaximal anodal stimulation disappeared after repeated topical applications of capsaicin, and reappeared one month after interruption of topical application. Conclusions: The results of this study confirm our hypothesis about the neurophysiological meaning of the two peaks. The double peak potential can have a diagnostic role in the distal sensory involvement, especially in the early stage when the distal impairment of nerve endings cannot be detected by standard evaluation of sensory nerve conduction.