Quick Discrimination of A delta and C Fiber Mediated Pain Based on Three Verbal Descriptors Florian Beissner 2 , Amadeus Brandau 1 , Christian Henke 2 , Lisa Felden 1 , Ulf Baumga ¨ rtner 3 , Rolf-Detlef Treede 3 , Bruno G. Oertel 1 , Jo ¨ rn Lo ¨ tsch 1 * 1 pharmazentrum frankfurt/The Center for Drug Research, Development and Safety (ZAFES), Institute of Clinical Pharmacology, Goethe-University, Frankfurt am Main, Germany, 2 Clinic of Neurology, Goethe-University, Frankfurt am Main, Germany, 3 Division of Neurophysiology, Center of Biomedicine and Medical Technology Mannheim (CBTM), Medical Faculty Mannheim, Ruprecht-Karls-University Heidelberg, Mannheim, Germany Abstract Background: A d 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 A d 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 A d 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 A d 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 A d 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 A d 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. Citation: Beissner F, Brandau A, Henke C, Felden L, Baumga ¨rtner U, et al. (2010) Quick Discrimination of A delta and C Fiber Mediated Pain Based on Three Verbal Descriptors. PLoS ONE 5(9): e12944. doi:10.1371/journal.pone.0012944 Editor: Kazutaka Ikeda, Tokyo Institute of Psychiatry, Japan Received June 18, 2010; Accepted August 31, 2010; Published September 23, 2010 Copyright: ß 2010 Beissner et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: FB was financially supported by the Horst Goertz Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: j.loetsch@em.uni-frankfurt.de Introduction In most medical settings, pain has a high prevalence with 61% in emergency medical care [1], almost 75% in patients reporting to general practice facilities [2], and with 12–80% chronic pain believed to affect the population [3]. It is therefore conceivable that the WHO advises for pain treatment as one of the major medical challenges. This is reflected by a broad research activity leading to a growing understanding of the pathophysiology of different pain syndromes. A d and C fibers, as the major pain- conducting nerve fiber systems, are involved to a different extent in these syndromes. For example, central sensitization to sensory input from A d fibers likely explains the response observed in the secondary zone of hyperalgesia [4], whereas in postherpetic neuralgia both fiber types are affected [5]. The fiber systems also show differences in their responsiveness to analgesics like opioids, which attenuate noxious C fiber input more potently than noxious A d fiber input [6,7]. Fiber specificity also plays an important role in experimental pain. For example, punctate and blunt pressure stimuli produce pain transmitted via small myelinated A d and non- myelinated C fibers respectively [4,8,9,10]. With the help of these specific stimuli, typically occurring pain qualities can be studied. The differentiation of the nerve fiber systems transmitting these pain sensations is possible most sensitively by invasive methods such as microneurography. However, these sophisticated tests often cannot be carried out. A quick test providing fiber discrimination in experiments or at the patient bed to assess nerve fiber involvement in painful diseases is not available. Therefore, the objective of this study was to create a valid pain questionnaire that allows to discriminate quickly between pain transmitted via A d fibers and pain transmitted via C fibers. The development of the test originated from the McGill pain questionnaire [11], as it provided a large and well established set of verbal descriptors of the pain sensation to choose. Mechanical and non-mechanical induced pain stimuli were applied to healthy volunteers, who chose the descriptors that best matched their sensations. Methods Study design In a single-blinded study design pain stimuli were applied by a single investigator on the arm or hand of the subjects, who were comfortably seated behind a black curtain shielding the subjects’ view on the stimulus application. Subjects were informed about PLoS ONE | www.plosone.org 1 September 2010 | Volume 5 | Issue 9 | e12944