Quick Discrimination of Adelta and C Fiber Mediated Pain Based on Three Verbal Descriptors

Background: Ad and C fibers are the major pain-conducting nerve fibers, activate only partly the same brain areas, and are differently involved in pain syndromes. Whether a stimulus excites predominantly Ad or C fibers is a commonly asked question in basic pain research but a quick test was lacking so far. Methodology/Principal Findings: Of 77 verbal descriptors of pain sensations, pricking'', dull'' and pressing'' distinguished best (95% cases correctly) between Ad fiber mediated (punctate pressure produced by means of von Frey hairs) and C fiber mediated (blunt pressure) pain, applied to healthy volunteers in experiment 1. The sensation was assigned to Ad fibers when pricking'' but neither dull'' nor pressing'' were chosen, and to C fibers when the sum of the selections of dull'' or pressing'' was greater than that of the selection of pricking''. In experiment 2, with an independent cohort, the three-descriptor questionnaire achieved sensitivity and specificity above 0.95 for distinguishing fiber preferential non-mechanical induced pain (laser heat, exciting Ad fibers, and 5-Hz electric stimulation, exciting C fibers). Conclusion: A three-item verbal rating test using the words pricking'', dull'', and pressing'' may provide sufficient information to characterize a pain sensation evoked by a physical stimulus as transmitted via Ad or via C fibers. It meets the criteria of a screening test by being easy to administer, taking little time, being comfortable in handling, and inexpensive while providing high specificity for relevant information.