• Ruth Defrin, Marshall Devor, and Silviu Brill.
• Department of Physical Therapy, School of Allied Health Professions, The Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv 69978, Israel Department of Cell and Developmental Biology, Institute of Life Sciences, and Center for Research on Pain, The Hebrew University of Jerusalem, Jerusalem 91904, Israel Institute of Pain Medicine, Department of Anesthesia and Critical Care Medicine, Tel Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel-Aviv 69978, Israel.
• Pain. 2014 Dec 1; 155 (12): 2551-2559.

AbstractWe report a novel symptom in many patients with low back pain (LBP) that sheds new light on the underlying pain mechanism. By means of quantitative sensory testing, we compared patients with radicular LBP (sciatica), axial LBP (LBP without radiation into the leg), and healthy controls, searching for cutaneous allodynia in response to weak tactile and cooling stimuli on the leg and low back. Most patients with radicular pain (~60%) reported static and dynamic tactile allodynia, as well as cooling allodynia, on the leg, often extending into the foot. Some also reported allodynia on the low back. In axial LBP, allodynia was almost exclusively on the back. The degree of dynamic tactile allodynia correlated with the degree of background pain. The presence of allodynia suggests that the peripheral nerve generators of background leg and back pain have also induced central sensitization. The distal (foot) location of the allodynia in patients who have it indicates that the nociceptive drive that maintains the central sensitization arises paraspinally (ectopically) in injured ventral ramus afferents; this is not an instance of somatic referred pain. The presence of central sensitization also provides the first cogent account of shooting pain in sciatica as a wave of activity sweeping vectorially across the width of the sensitized dorsal horn. Finally, the results endorse leg allodynia as a pain biomarker in animal research on LBP, which is commonly used but has not been previously validated. In addition to informing the underlying mechanism of LBP, bedside mapping of allodynia might have practical implications for prognosis and treatment.Copyright © 2014 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

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