Characteristics of Sensitization Associated With Chronic Pain Conditions

Abstract

Objectives To describe and understand varieties and characteristics of sensitization contributing to hyperalgesia for patients with chronic pain conditions. Methods Thermal stimulation was delivered to the face, forearm and calf of pain-free subjects and individuals with irritable bowel syndrome (IBS), temporomandibular pain disorder (TMD) and fibromyalgia syndrome (FMS). Three second contacts of a preheated thermode occurred at 30 sec. intervals in ascending and then descending series (0.7°C steps). Results Thermal pain ratings during ascending series were greater at each site for individuals diagnosed with chronic pain. Strong 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 for all subjects was greater during descending series than during ascending series of arm and leg stimulation. The hypersensitivity during descending series was comparable for pain-free, FMS and TMD subjects but was increased in duration for arm or leg stimulation of FMS subjects. Discussion The widespread sensitization for IBS and TMD subjects 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 during 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 FMS patients reveals a unique influence of widespread chronic pain referred to deep somatic tissues.

Catechol-O-methyltransferase inhibition alters pain and anxiety-related volitional behaviors through activation of β-adrenergic receptors in the rat

“…Thus, past and present studies together provide behavioral evidence for COMT-dependent sensitization of both Aδ and C-thermal nociceptors. Further characterization of operant responses and nociceptor physiology during periods of low COMT activity may prove useful to the study of chronic pain, as patients with temporomandibular disorders and fibromyalgia have abnormal nociceptor function in response to a similar range of moderate to high intensity temperatures (Maixner et al, 1995, Maixner et al, 1998, Park et al, 2010, Vierck et al, 2014). …”

Discrepancy between stimulus response and tolerance of pain in Alzheimer disease

“…25 None of the studies evaluated stimulus-response functions, but their findings could be consistent with less steep stimulus-response curves. In the cognitively unimpaired, higher pain ratings and steeper stimulusresponse curves indicate increased pain sensitivity, 9 but this may not be the case in AD dementia. We found a similar pattern of habituation to repeated heat stimuli in patients and controls, indicating that the observed differences in stimulus-response function most likely are due to impairment of affective-motivational factors and not to differences in inherent sensory properties toward sensitization or habituation.…”

Comparison of operant escape and reflex tests of nociceptive sensitivity

“…In more complex paradigms, animals can be trained to respond at different times during prolonged or repetitive nociceptive stimulation, permitting descriptions of stimulus duration/response functions. Human psychophysical testing of nociceptive sensitivity can exploit prolonged stimulation (Vierck et al, , 2013b(Vierck et al, , 2014, which provides opportunities to understand factors which affect tonic clinical pain. In special paradigms involving prolonged stimulation, animals can learn to respond only when input from C nociceptors is ongoing or after temporal summation has occurred .…”

“…Detecting the elicited pain that is best associated with different forms of clinical pain may require special methods (e.g., repetitive or prolonged stimulation of certain types of peripheral afferent), making it challenging to resolve this issue for all pain conditions. However, simple testing of nociceptive sensitivity has revealed widespread sensitization to painful stimulation for a large number of pain conditions (Fernandez-de-las-Penas et al, 2011;Vierck, 2012;Vierck et al, 2014). Thus, if an animal model is representative of a clinical pain condition with ongoing pain, thoughtful choice of an operant conditioning paradigm should reveal abnormalities similar to those revealed by psychophysical testing of humans with the condition.…”