The journal of pain : official journal of the American Pain Society
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Females are disproportionately affected by irritable bowel syndrome (IBS) with menstrual cycle-dependent fluctuations in abdominal pain suggesting a role for ovarian hormones. IBS patients also exhibit greater activation of brain areas involved in pain affect such as the amygdala, yet the role of supraspinal processes in the effects of ovarian hormones on visceral pain is largely unexplored. The goal of the current study was to determine whether sex steroids act at the level of the amygdala to alter colonic pain sensitivity. Ovariectomized rats received implants on the amygdala of progesterone, estradiol, progesterone combined with estradiol, or cholesterol as a control to examine the involvement of the amygdala in ovarian hormone-mediated changes in visceral sensitivity. Visceral sensitivity was quantified as the number of abdominal contractions, a visceromotor response (VMR), in response to graded pressures of colorectal distension (CRD). Somatic sensitivity was also assessed by measuring the mechanical force required to elicit hindpaw withdrawal. Elevated levels of progesterone and/or estradiol on the amygdala heightened the responsiveness to CRD; in contrast, neither estradiol nor progesterone altered somatic sensation. Furthermore, administration of progesterone or estradiol to areas adjacent to the amygdala did not affect visceral sensitivity. Future studies will address the specific steroid receptors mediating the effects of progesterone and estradiol. ⋯ To our knowledge, this study represents the first description of a specific brain site mediating the effects of ovarian steroids on visceral sensitivity. These data also suggest that an amygdala-dependent mechanism may be responsible, at least in part, for the exacerbation of visceral symptomatology in females.
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To investigate the pain-modulatory effects of a local inflammatory stimulus on pain elsewhere in the body, capsaicin was applied topically to the forearm of 14 healthy female volunteers. Pressure-pain thresholds and sensitivity to sharpness were assessed on each side of the forehead twice per day during 48 hours of capsaicin treatment, and in the treated and contralateral forearm before and at the end of treatment. Heat was applied to the treated area to rekindle pain at times of forehead assessment. Hyperalgesia to sharpness, but not pressure pain, developed in the treated area whereas sensations remained stable in the contralateral forearm. Sharpness ratings decreased bilaterally in the forehead after 6 hours of treatment, and ipsilateral analgesia to pressure pain developed in the forehead when the capsaicin site was heated after 48 hours of treatment. These findings suggest that pain modulation involves unilateral regulatory mechanisms in addition to local and generalized pain control. The dissociated changes to sharpness and pressure pain indicate distinct cutaneous and deep central pain pathways. ⋯ The findings lend support to an increasing body of research which demonstrates that pain modulation involves hemilateral mechanisms in addition to local and generalized controls. Elucidation of mechanisms that modulate ipsilateral pain processing may help to clarify the pathophysiology of complex regional pain syndrome, which is characterized by hemilateral hyperalgesia.
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Single-word descriptors are commonly used to label and communicate pain in lay as well as clinical settings. Research has shown that the pool of 84 pain descriptors from the McGill Pain Questionnaire (MPQ) can be refined into a parsimonious subset of 36 descriptors that fit into 12 categories. However, the past 3 studies on this issue have been confined to college student samples. The present study investigated the classification structure and calibration of this new system of pain descriptors in 43 chronic pain patients. Employing a 3-point decision rule, a relatively unambiguous classification structure emerged with 3 descriptors for each of the 12 categories. Within and across categories, the intensities implied by these words could be meaningfully rank ordered. The intensities correlated positively and significantly with those previously derived from student samples as well as those of matching MPQ words previously rated by pain patients. This confirms the stability of the intensity ratings of pain words. Information theoretic analysis revealed transmission of 83% of the maximum (3.6 bits) potentially transmissible in a system of such configuration. This lends support to the idea that the 36 pain descriptors are parsimonious and can be used with efficiency to describe chronic pain. ⋯ This study found that in the English language, 36 words (classified into 12 subcategories) can be efficiently used to describe pain. These words can also be reliably ordered in terms of implied pain intensity. This has implications for the qualitative and quantitative assessment of pain patients.
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Persistent shoulder pain is a common complication after stroke. Its etiology and underlying mechanisms are not well understood and treatment is generally unsatisfactory. The objective of this study was to assess the role of central sensitization and disinhibition in chronic stroke patients with chronic PSSP (n = 19), pain-free stroke patients (n = 29), and healthy controls (n = 23). Positive and negative somatosensory symptoms and signs were assessed using clinical examination and electrical and mechanical quantitative sensory testing (QST). Conditioned pain modulation (CPM) was assessed by comparing QST thresholds before and after applying a cold pressor test. Sensory abnormalities were more frequently observed and more severe in patients with PSSP, including positive signs such as allodynia at the affected side and generalized hyperalgesia at the unaffected side. CPM was similar in stroke patients and healthy controls. This study showed that chronic PSSP was associated with several positive and negative somatosensory signs, implicating a role for central sensitization and possibly for disinhibition. Since the causal relationship remains unclear, and may be related to either neuroplasticity induced by ongoing nociception as well as to the neuropathic brain lesion, prospective studies are warranted. ⋯ The assessment of somatosensory symptoms and signs and endogenous pain modulation demonstrated a role for central sensitization and possibly for disinhibition in chronic PSSP. Prevention and treatment of PSSP could benefit from a more detailed analysis of both peripheral and central pain mechanisms.
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The primary objective of the present study was to examine the relative importance of pain behaviors and judgmental heuristics (eg, gender stereotypes) in observers' inferences about pain intensity and pain genuineness. Participants (n = 90) observed video depictions of chronic pain patients performing a physically challenging task and were asked to make inferences of pain intensity and pain genuineness. Analyses indicated that observers relied on judgmental heuristics and pain behaviors both when making inferences about pain intensity and when making inferences about pain genuineness. Follow-up analyses, however, revealed that judgmental heuristics (eg, gender stereotypes) were significantly less utilized when observers made inferences about pain genuineness than when observers made inferences about pain intensity. When observers made inferences about pain genuineness, analyses indicated that patients' facial pain behaviors became the most important source of information. Taken together, these findings suggest that observers who are asked to make inferences about the genuineness of others' pain are likely to reduce their reliance on judgmental heuristics in favor of more controlled and thoughtful inferential processes characterized by detailed processing of behavioral information, particularly others' facial pain behaviors. ⋯ The current study provides new insights into the processes that are involved in observers' inferences about pain intensity and pain genuineness. These inferences play an important role in treatment decisions and advances in this domain could ultimately contribute to more effective management of the challenges facing patients with pain-related disorders.