• Charles J Vierck, Fong Wong, Christopher D King, Andre P Mauderli, Siegfried Schmidt, and Joseph L Riley.
• Departments of ‡Behavioral Science †Prosthodontics, College of Dentistry Departments of §Community Health and Family Medicine *Neuroscience, College of Medicine, University of Florida, Gainesville, FL.
• Clin J Pain. 2014 Feb 1; 30 (2): 119128119-28.

ObjectivesTo describe and understand varieties and characteristics of sensitization contributing to hyperalgesia in participants with chronic pain conditions.MethodsThermal stimulation was delivered to the face, forearm, and calf of pain-free participants and individuals with irritable bowel syndrome, temporomandibular pain disorder (TMD), and fibromyalgia syndrome (FM). Three-second contacts by a preheated thermode occurred at 30-second intervals in ascending and then in descending series (0.7°C steps).ResultsThermal pain ratings during ascending series were greater at each site in individuals diagnosed with chronic pain. Intense pain at the time of testing further enhanced the ratings at all sites, but mild or moderate clinical pain did not have this effect. Thermal pain in all participants was greater during descending series compared with the ascending series of arm and leg stimulation. The hypersensitivity during the descending series was comparable in pain-free, FM and TMD participants but was increased in duration for arm or leg stimulation of FM participants.DiscussionThe widespread sensitization for irritable bowel syndrome and TMD participants does not rely on mechanisms of spatial and temporal summation often invoked to explain widespread hyperalgesia associated with chronic pain. Increased sensitivity during descending series of stimulation of an arm or leg but not the face indicates a propensity for sensitization of nociceptive input to the spinal cord. Abnormally prolonged sensitization for FM participants reveals a unique influence of widespread chronic pain referred to deep somatic tissues.

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