Characteristics of Sensitization Associated With Chronic Pain Conditions (original) (raw)
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Psychophysical measures of sensitization to tonic heat discriminate chronic pain patients
Pain, 1999
Sensitization to continued nociceptive stimulation is supposed to be involved in the development of chronic pain at several levels of the CNS, but experimental studies investigating the perceptual dynamics of sensitization in humans are rare, and the diagnostic validity of experimental pain models is not known. The present study used a tonic heat paradigm to assess early sensitization (15-100 s) to experimental pain in 30 chronic pain patients (15 musculoskeletal/back pain, 15 headache) and 23 healthy controls. Change in pain sensation during prolonged stimulation was measured by a dual sensitization method which combines subjective ratings and behavioural responses in an indirect psychophysical protocol protected against response bias. Phasic and tonic pain thresholds were measured for control purposes. The degree of sensitization was linearly related to stimulus temperature, and groups differed significantly in this 'sensitization gradient': chronic pain patients sensitized earlier and stronger than healthy subjects, musculoskeletal pain patients showed the strongest effect. Pain thresholds were lowered in headache patients only. Discriminant analysis demonstrated good sensitivity and specificity of individual sensitization measures for distinguishing pain syndromes, particularly in combination with pain thresholds. The results are in accordance with current models of spinal plasticity contributing to pathological pain states. They argue for the diagnostic value of psychophysical measures of sensitization.
Extreme thermal sensitivity and pain-induced sensitization in a fibromyalgia patient
Pain research and treatment, 2010
During the course of a psychophysical study of fibromyalgia syndrome (FMS), one of the subjects with a long history of headache and facial pain displayed an extraordinarily severe thermal allodynia. Her stimulus-response function for ratings of cutaneous heat pain revealed a sensitivity clearly beyond that of normal controls and most FMS subjects. Specially designed psychophysical methods showed that heat sensitivity sometimes increased dramatically within a series of stimuli. Prior exposure to moderate heat pain served as a trigger for allodynic ratings of series of normally neutral thermal stimulation. These observations document a case of breakthrough pain sensitivity with implications for mechanisms of FMS pain.
The Journal of Pain, 2007
Temporal summation of second pain (TSSP) results from repetitive stimulation of peripheral C-fibers (> 0.33 Hz) and is thought to reflect summation mechanisms of dorsal horn neurons (i.e., windup). Both TSSP and windup result in short term enhancement of C fiber-evoked responses that decay rapidly after the end of stimulation. However, very low stimulus frequencies (0.17-0.08 Hz) can maintain this enhancement after TSSP and windup have occurred. This maintained enhancement is termed TSSP-maintenance (TSSP-M) and is indicative of central sensitization. TSSP-M may be especially relevant for chronic pain conditions such as fibromyalgia (FM) and may play an important role in its pathogenesis. Whereas TSSP-M of heat induced pain is well characterized in human subjects at spinal cord levels related to the upper body, TSSP-M at spinal levels related to the lower body has not been previously studied. The present study was designed to evoke TSSP-M at the upper and lower extremities of normal controls (NC) and FM patients and thus characterize their spatial distribution of central sensitization. Twenty-three NC and twenty-six FM patients were enrolled in this study. TSSP-M testing consisted of repetitive heat pain stimulation at the thenar eminences of the hands or feet. The subjects rated the pain intensity of repetitive heat stimuli as well as 15 sec and 30 sec pain aftersensations. The experiments demonstrated significant TSSP-M for both NC and FM patients. In contrast to NC, TSSP-M ratings of heat stimuli were increased in FM patients and their TSSP-aftersensations were prolonged. There was, however, no statistical difference between TSSP-M ratings or TSSP-aftersensations at the hands or feet in either NC or FM patients. These findings demonstrate that central sensitization of FM patients is widespread and similar along the spinal neuroaxis. Perspective-The pain of FM seems to be accompanied by generalized central sensitization, involving the length of the spinal neuroaxis. Thus, widespread central sensitization appears to be a hallmark of FM and may be useful for the clinical case definition of this prevalent pain syndrome. In addition, measures of widespread central sensitization, like TSSP-M could also be used to assess treatment responses of FM patients.
Heat hyperalgesia in humans: assessed by different stimulus temperature profiles
European Journal of Pain, 2002
The aim of the present study was to investigate the effect of the rate of temperature increase on the intensity of the evoked pain before and after hyperalgesia induced by topical capsaicin. Further, hyperalgesia to suprathreshold heat stimuli was investigated. Thirteen healthy volunteers were included in the experiment. All stimuli were applied in randomised order within the volar surface of both forearms using a computer-controlled contact stimulator. In one of the forearms, the effect of the rate of temperature change was investigated for 1.0, 5.0, and 8.0°C/s reaching a peak temperature of 30.0, 33.0, 36.0, 39.0, and 42.0°C in the primary hyperalgesic area and reaching a peak temperature of 33.0, 36.0, 39.0, 42.0, 45.0, 47.0, and 49.0°C in the secondary hyperalgesic area before and after the induction of hyperalgesia. In the other forearm, the same procedure was repeated without capsaicin application as a control measurement. After the induction of hyperalgesia, the pain ratings were significantly higher in the arm treated with capsaicin compared with baseline for 36, 39, and 42°C heating rates in the primary hyperalgesic area. The pain ratings were significantly higher with 1°C/s heating rate compared with 5 and 8°C/s for 36, 39, and 42°C in the primary hyperalgesic area. Heat hyperalgesia was also observed within the secondary hyperalgesic area to pin-prick for stimulus temperatures of 45, 47, and 49°C compared with the baseline measurements. Increased ratings were found for all three heating rates in the secondary hyperalgesic area. There were no heat hyperalgesia in the control arm. In conclusion, hyperalgesia to suprathreshold heat stimuli was observed in the secondary hyperalgesic area and C-fibres play an important role in the primary hyperalgesia to heat.
European Journal of Pain, 2003
The increased use of quantitative sensory testing in the study of pain raises the need to characterize various aspects of psychophysical response to noxious stimulation in healthy subjects. The present study aims to address several issues regarding the use of heat pain stimuli: (a) Are pain scores for short-term repeated phasic stimuli consistent? (b) Does an exposure to tonic heat pain stimulus cause sensitization and change the scores for subsequent phasic stimuli? and (c) Are pain scores for phasic and tonic heat pain correlated? To address these questions, a series of four phasic heat pain stimuli of 47°C were given to the forearms of 70 healthy volunteers, over the course of an hour. Pain scores by Visual Analog Scale (VAS) were obtained for each stimulus. In 50 subjects, a tonic heat pain of 70 s duration at 47.5°C was given between the first and second phasic stimuli. Pain scores were obtained at four points along this tonic stimulus. Repeated measures ANOVA and a sensitive post hoc analysis indicated that, while the pain perception was reduced on the second, nearly immediate trial, subsequent VAS scores of pain perception were not different from the first (#1: 35:2 AE 19:2; #2: 31:4 AE 20:2, #3: 33:0 AE 21:6; and #4: 33:2 AE 20:1, respectively), with strong correlation among the phasic tests. The average tonic pain score was 53:7 AE 23:1. Administration of tonic pain stimuli did not result in different VAS scores of subsequent phasic pain stimuli, compared to those subjects who did not receive tonic pain stimuli. Tonic and phasic pain were positively correlated (e.g., r ¼ 0:45; p < 0:001 for the first phasic stimuli). However, no relation was found between the level of perceived pain, either for phasic or for tonic stimuli, and presence or absence of temporal summation during the tonic pain. In conclusion: (i) phasic pain scores assessments at 30 0 and 60 0 after baseline is consistent; (ii) tonic heat pain, despite relatively high VAS scores, does not cause a change in the scoring of subsequent phasic stimuli; and (iii) phasic and tonic pain scores correlate with each other. Thus, the normal pattern of pain perception is stable and not altered by single tonic pain stimulation.
PAIN, 2009
Females with Irritable Bowel Syndrome (IBS) and Temporomandibular Disorder (TMD) are characterized by enhanced sensitivity to experimental pain. One possible explanation for this observation is deficiencies in pain modulation systems like Diffuse Noxious Inhibitory Control (DNIC). In a few studies that used brief stimuli, chronic pain patients demonstrate reduced DNIC. The purpose of this study was to compare sensitivity to prolonged heat pain and the efficacy of DNIC in controls to IBS and TMD patients. Heat pain (experimental stimulus; 44.0-49.0°C), which was applied to left palm, was continuously rated during three 30-second trials across three separate testing sessions under the following conditions: without a conditioning stimulus; during concurrent immersion of the right foot in a 23.0°C (control); and during noxious cold immersion in a (DNIC; 8.0-16.0°C) water bath. Compared to controls, IBS and TMD patients reported increased sensitivity to heat pain and failed to demonstrate pain inhibition due to DNIC. Controls showed a significant reduction in pain during the DNIC session. These findings support the idea that chronic pain patients are not only more pain sensitive and demonstrate reduced pain inhibition by pain, possibly because of dysfunction of endogenous pain inhibition systems.
Current Rheumatology Reports, 2010
Fibromyalgia syndrome (FM) is a highly prevalent musculoskeletal disorder that is often accompanied by somatic hyperalgesia (enhanced pain from noxious stimuli). Neural mechanisms of somatic hyperalgesia have been analyzed via quantitative sensory testing of FM patients. Results of these studies suggest that FM pain is associated with widespread primary and secondary cutaneous hyperalgesia, which are dynamically maintained by tonic impulse input from deep tissues and likely by brain-to-spinal cord facilitation. Enhanced somatic pains are accompanied by mechanical hyperalgesia and allodynia in FM patients as compared with healthy controls. FM pain is likely to be at least partially maintained by peripheral impulse input from deep tissues. This conclusion is supported by results of several studies showing that injection of local anesthetics into painful muscles normalizes somatic hyperalgesia in FM patients.
The Journal of Pain, 2012
Multiple abnormalities in pain processing have been reported in patients with chronic musculoskeletal pain syndromes. These changes include mechanical and thermal hyperalgesia, decreased thresholds to mechanical and thermal stimuli (allodynia), and central sensitization, all of which are fundamental to the generation of clinical pain. Therefore, we hypothesized that quantitative sensory tests may provide useful predictors of clinical pain intensity of such patients. Our previous studies of fibromyalgia (FM) patients have shown statistically significant correlations of quantitative sensory test results with clinical pain intensity, including mechanical spatial summation, number of pain areas, wind-up, and wind-up aftersensations. Although these tests predicted up to 59% of the variance in FM clinical pain intensity, their expense and technical complexities limited widespread use in clinical practice and trials. Thus, we developed practical tests of primary (mechanical) and secondary (heat) hyperalgesia that also strongly predict clinical pain intensity in patients with chronic musculoskeletal pain disorders. Thirty-six individuals with FM, 24 with local musculoskeletal pain, and 23 normal controls underwent testing of mechanical and heat hyperalgesia at the shoulders and hands. All subjects rated experimental pains using an electronic visual analog scale. Using either heat or pressure pain ratings as well as tender point counts and negative affect as predictors, up to 49.4% of the patients' variance of clinical pain intensity could be estimated. Results of this study emphasize the important contributions of peripheral and central factors to both local and widespread chronic pain. Overall, measures of mechanical and heat hyperalgesia in combination with tender point and negative affect provided powerful predictors of clinical pain intensity in chronic musculoskeletal pain patients that can be readily used in clinical practice and trials. Perspective-Simple tests of mechanical and heat hyperalgesia can predict large proportions of the variance in clinical pain intensity of chronic musculoskeletal pain patients and thus are feasible to be included in clinical practice and clinical trials.