Mechanical block of large myelinated fibres in healthy humans to demonstrate that paroxysmal pain is mediated by non-nociceptive fibres

Abstract

We aimed at testing whether paroxysmal pain is selectively mediated by large myelinated A-beta fibres. To do so we verified whether the selective block of A-beta fibres suppresses paroxysmal pain elicited by high-frequency, low intensity electrical stimulation. In five healthy participants, we delivered a high-frequency (100 Hz), low-intensity (5–8 mA) electrical stimulation in the radial nerve territory and rated the intensity of perceived pain using a NRS scale (0–10). We then applied a mechanical block of the radial nerve using a rubber band, connected to a 750 g weight at each end, across the distal part of the forearm. We have used quantitative sensory testing and laser evoked potentials to assess afferent nerve fibre function during the mechanical block. After 35 ± 10 min the mechanical block abolished both the paroxysmal painful sensation elicited by high-frequency, low intensity electrical stimulation and the tactile sensation, as assessed with von Frey hairs. Conversely, thermal-pain thresholds and laser evoked potentials were spared. Our data showing that the mechanical block of large myelinated A-beta fibre abolishes paroxysmal pain indicates that this type of pain is selectively mediated by non-nociceptive A-beta fibres.