Altered Pain Sensitivity in Elderly Women with Chronic Neck Pain

Background

Age-related changes occur in both the peripheral and central nervous system, yet little is known about the influence of chronic pain on pain sensitivity in older persons. The aim of this study was to investigate pain sensitivity in elders with chronic neck pain compared to healthy elders.

Methods

Thirty elderly women with chronic neck pain and 30 controls were recruited. Measures of pain sensitivity included pressure pain thresholds, heat/cold pain thresholds and suprathreshold heat pain responses. The pain measures were assessed over the cervical spine and at a remote site, the tibialis anterior muscle.

Results

Elders with chronic neck pain had lower pressure pain threshold over the articular pillar of C5-C6 and decreased cold pain thresholds over the cervical spine and tibialis anterior muscle when compared with controls (p < 0.05). There were no between group differences in heat pain thresholds and suprathreshold heat pain responses (p > 0.05).

Conclusion

The presence of pain hypersensitivity in elderly women with chronic neck pain appears to be dependent on types of painful stimuli. This may reflect changes in the peripheral and central nervous system with age.     

Suprathreshold Heat Pain Response Predicts Activity-Related Pain,but Not Rest-Related Pain,in an Exercise-Induced Injury Model

Exercise-induced injury models are advantageous for studying pain since the onset of pain is controlled and both pre-injury and post-injury factors can be utilized as explanatory variables or predictors. In these studies, rest-related pain is often considered the primary dependent variable or outcome, as opposed to a measure of activity-related pain. Additionally, few studies include pain sensitivity measures as predictors. In this study, we examined the influence of pre-injury and post-injury factors, including pain sensitivity, for induced rest and activity-related pain following exercise induced muscle injury. The overall goal of this investigation was to determine if there were convergent or divergent predictors of rest and activity-related pain. One hundred forty-three participants provided demographic, psychological, and pain sensitivity information and underwent a standard fatigue trial of resistance exercise to induce injury of the dominant shoulder. Pain at rest and during active and resisted shoulder motion were measured at 48- and 96-hours post-injury. Separate hierarchical models were generated for assessing the influence of pre-injury and post-injury factors on 48- and 96-hour rest-related and activity-related pain. Overall, we did not find a universal predictor of pain across all models. However, pre-injury and post-injury suprathreshold heat pain response (SHPR), a pain sensitivity measure, was a consistent predictor of activity-related pain, even after controlling for known psychological factors. These results suggest there is differential prediction of pain. A measure of pain sensitivity such as SHPR appears more influential for activity-related pain, but not rest-related pain, and may reflect different underlying processes involved during pain appraisal.     

Pain issues in poultry

This review highlights the possible pain experienced by layer and broiler poultry in modern husbandry conditions. Receptors which respond to noxous stimulation (nociceptors) have been identified and physiologically characterised in many different part of the body of the chicken including the beak, mouth, nose, joint capsule and scaly skin. Stimulation of these nociceptors produces cardiovascular and behavioural changes consistent with those seen in mammals and are indicative of pain perception. Physiological and behavioural experiments have identified the problem of acute pain following beak trimming in chicks, shackling, and feather pecking and environmental pollution. Chronic pain is a much greater welfare problem because it can last for long periods of time from weeks to months. Evidence for possible chronic pain is presented from a variety of different conditions including beak trimming in older birds, orthopaedic disease in broiler and bone breakage in laying hens. Experiments on pain in the chicken have not only identified acute and chronically painful conditions but also have provided information on qualitative differences in the pain experienced as well as identifying a cognitive component providing evidence of conscious pain perception.     

Individual and Gender Differences in Subjective and Objective Indices of Pain: Gender,Fear of Pain,Pain Catastrophizing and Cardiovascular Reactivity

According to fear-avoidance models of pain perception, heightened fear of pain may increase disruptive effects of pain; however, the extent to which this affects self-reported pain severity versus physiological indices of pain is not well delineated. The current study examined self-report measures and physiological indices of pain during a cold pressor (CP) task. Individual differences in fear of pain and pain catastrophizing were also assessed via questionnaire. The primary aim of the current study was to examine the extent to which individual differences associated with fear and catastrophizing in response to pain influences subjective and physiological measures of pain. A secondary aim was to examine gender differences associated with response to pain. Average subjective pain ratings were higher for females than males. In contrast, males exhibited higher systolic and diastolic reactivity in response to the CP task relative to females, as well as failure to fully recover to baseline levels. Follow-up correlational analyses revealed that subjective pain ratings were positively associated with fear of pain in both sexes, but were not associated with cardiovascular indices. These results suggest that fear of pain and pain catastrophizing do not influence cardiovascular responses to induced pain. Further research is necessary in order to determine whether these gender differences in blood pressure and heart rate response profiles are due to biological or psychosocial influences. Results support the notion that fear of pain increases subjective pain ratings, but does not influence cardiovascular responses during CP pain-induction.     

Pain genes

Pain, which afflicts up to 20% of the population at any time, provides both a massive therapeutic challenge and a route to understanding mechanisms in the nervous system. Specialised sensory neurons (nociceptors) signal the existence of tissue damage to the central nervous system (CNS), where pain is represented in a complex matrix involving many CNS structures. Genetic approaches to investigating pain pathways using model organisms have identified the molecular nature of the transducers, regulatory mechanisms involved in changing neuronal activity, as well as the critical role of immune system cells in driving pain pathways. In man, mapping of human pain mutants as well as twin studies and association studies of altered pain behaviour have identified important regulators of the pain system. In turn, new drug targets for chronic pain treatment have been validated in transgenic mouse studies. Thus, genetic studies of pain pathways have complemented the traditional neuroscience approaches of electrophysiology and pharmacology to give us fresh insights into the molecular basis of pain perception.     

Basolateral Amygdala Lesion Inhibits the Development of Pain Chronicity in Neuropathic Pain Rats

Background

Chronicity of pain is one of the most interesting questions in chronic pain study. Clinical and experimental data suggest that supraspinal areas responsible for negative emotions such as depression and anxiety contribute to the chronicity of pain. The amygdala is suspected to be a potential structure for the pain chronicity due to its critical role in processing negative emotions and pain information.

Objective

This study aimed to investigate whether amygdala or its subregions, the basolateral amygdala (BLA) and the central medial amygdala (CeA), contributes to the pain chronicity in the spared nerve injury (SNI)-induced neuropathic pain model of rats.

Methodology/Principal Findings

(1) Before the establishment of the SNI-induced neuropathic pain model of rats, lesion of the amygdaloid complex with stereotaxic injection of ibotenic acid (IBO) alleviated mechanical allodynia significantly at days 7 and 14, even no mechanical allodynia at day 28 after SNI; Lesion of the BLA, but not the CeA had similar effects; (2) however, 7 days after SNI when the neuropathic pain model was established, lesion of the amygdala complex or the BLA or the CeA, mechanical allodynia was not affected.

Conclusion

These results suggest that BLA activities in the early stage after nerve injury might be crucial to the development of pain chronicity, and amygdala-related negative emotions and pain-related memories could promote pain chronicity.     

Pain sensitivity in obesity

Pain sensitivity of the obese and control women was investigated using an electrophysiological method. The sensory and pain threshold were higher in the obese than in the control subjects. Pain sensitivity of the control as well as that of the obese women increased significantly during the day from morning to evening. The circadian rhythm of the sensory and pain thresholds with peak values (acrophase) in the morning was significant only in control women. Weight reducing treatment did not change the pain sensitivity in obese women.     

Pain perception in competitive swimmers.

The pain perception of 30 competitive swimmers was studied using experimentally induced ischaemic pain. The pain thresholds and tolerances of this group were compared with those of 30 club swimmers and 26 non-competitive athletes. While pain thresholds showed little difference between the groups, pain tolerances were considerably different. Pain tolerances of the competitive swimmers varied according to the stage of the training season. The relation between ischaemic pain and that experienced during swimming training was studied using a pain questionnaire composed of several systematically structured verbal categories. Both types of pain were classified along similar dimensions, and it was concluded that the experimentally demonstrated pain tolerances could be generalized to the normal pain perception of the subjects. The origins of the enhanced pain tolerances of the competitive swimmers would seem to lie in their systematic exposure to brief periods of intense pain. These data could have relevance for the treatment of chronic pain in certain diseases.     

Pain in Multiple Myeloma

Seventy-two patients with multiple myeloma were surveyed with respect to the causation of pain. Almost all of those who had an abrupt onset of pain showed a fracture at the site of pain. About one-half of those with a gradual onset of pain also had a fracture. The great majority of osteolytic lesions were painless. The relief afforded by local irradiation, which could not have been due to healing of the fracture, may have been due to an effect on extruded tumour tissue.     

Pain research in China

In addition to investigating the anatomy,neurochemistry and neurophysiology of pain pathways,Chinese researchers have extended their work into the molecular and cellular mechanisms of sensory afferent transmission at the spinal cord level as well as cognitive processing in the brain.The mechanism underlying acupuncture analgesia remains a subject of special interest for Chinese pain researchers,with the aim of combining clinical practice with the understanding of pain transmission and analgesic mechanism.     

Role of Astrocytes in Pain

Over the last decade, a series of studies has demonstrated that glia in the central nervous system play roles in many aspects of neuronal functioning including pain processing. Peripheral tissue damage or inflammation initiates signals that alter the function of the glial cells (microglia and astrocytes in particular), which in turn release factors that regulate nociceptive neuronal excitability. Like immune cells, these glial cells not only react at sites of central and/or peripheral nervous system damage but also exert their action at remote sites from the focus of injury or disease. As well as extensive evidence of microglial involvement in various pain states, there is also documentation that astrocytes are involved, sometimes seemingly playing a more dominant role than microglia. The interactions between astrocytes, microglia and neurons are now recognized as fundamental mechanisms underlying acute and chronic pain states. This review focuses on recent advances in understanding of the role of astrocytes in pain states.     

A Pain in the Fetus: Toward Ending Confusion about Fetal Pain

Are fetuses, at any stage of their development, capable of feeling pain? In his paper, ‘Locating the Beginnings of Pain’, Stuart Derbyshire argues that they are not. We argue that he reaches this conclusion by way of conceptual confusion, a misreading of the available scientific data and the inclusion of irrelevant data. Despite his assertion to the contrary, the work of most scientists in the area supports the conclusion that fetuses can feel pain. At the outset we examine the concept of pain and distinguish it from the allied concept of nociception, with which it is sometimes confused. With the relevant conceptual framework in place, we elucidate the problem of determining when, in its development, a human becomes capable of feeling pain. We then examine the available data showing how, on balance, it tends more to support than undermine the claim that fetuses of around 28 to 30 weeks' gestation are capable of feeling pain.     

Dopamine Precursor Depletion Influences Pain Affect Rather than Pain Sensation

Pain is a multidimensional experience, which includes sensory, cognitive, and affective aspects. Converging lines of evidence indicate that dopaminergic neurotransmission plays an important role in human pain perception. However, the precise effects of dopamine on different aspects of pain perception remain to be elucidated. To address this question, we experimentally decreased dopaminergic neurotransmission in 22 healthy human subjects using Acute Phenylalanine and Tyrosine Depletion (APTD). During APTD and a control condition we applied brief painful laser stimuli to the hand, assessed different aspects of pain perception, and recorded electroencephalographic responses. APTD-induced decreases of cerebral dopaminergic activity did not influence sensory aspects of pain perception. In contrast, APTD yielded increases of pain unpleasantness. The increases of unpleasantness ratings positively correlated with effectiveness of APTD. Our finding of an influence of dopaminergic neurotransmission on affective but not sensory aspects of phasic pain suggests that analgesic effects of dopamine might be mediated by indirect effects on pain affect rather than by direct effects on ascending nociceptive signals. These findings contribute to our understanding of the complex relationship between dopamine and pain perception, which may play a role in various clinical pain states.     

慢性疼痛与皮层-边缘系统

慢性疼痛作为最常见的临床症状之一,已被认为是全球性的公共健康问题.然而,目前急性疼痛转化为慢性疼痛(即疼痛慢性化)的机制尚不清楚,如何防治急性疼痛转化为慢性疼痛仍然是临床亟待解决的问题.影像学研究表明,编码疼痛情绪、动机和记忆的脑区涉及皮层-边缘系统,而编码持续性疼痛的脑区也主要涉及该系统.基于此,本文概述了慢性疼痛患者在情绪、动机和记忆等方面的行为异常,并详细讨论了慢性疼痛患者皮层-边缘系统的结构和功能变化.其次,本文以慢性腰背痛为例,总结了可能预测疼痛慢性化的影像学指标,如内侧前额叶皮层与伏隔核以及海马的功能连接、背内侧前额叶皮层-杏仁核-伏隔核之间的功能连接均可预测1年后腰背痛疼痛慢性化的发展.此外,基于现有的疼痛慢性化理论模型,本文指出疼痛慢性化可能涉及患者对负面情绪的强化学习以及奖赏和应激系统的功能失调.最后,根据目前研究仍存在的问题和局限,本文对未来的研究方向和方法提出了建议.     

Pain assessment in animal models of osteoarthritis

Assessment of pain in animal models of osteoarthritis is integral to interpretation of a model's utility in representing the clinical condition, and enabling accurate translational medicine. Here we describe behavioral pain assessments available for small and large experimental osteoarthritic pain animal models.     

Phasic and Tonic Pain Differentially Impact the Interruptive Function of Pain

The interruptive effect of painful experimental stimulation on cognitive processes is a well-known phenomenon. This study investigated the influence of pain duration on the negative effects of pain on cognition. Thirty-four healthy volunteers performed a rapid serial visual presentation task (RSVP) in which subjects had to detect (visual detection task) and count the occurrence of a target letter (working memory task) in two separate sessions while being stimulated on the left volar forearm with either short (2 sec) or long (18 sec) painful heat stimuli of equal subjective intensity. The results show that subjects performed significantly worse in the long pain session as indexed by decreased detection and counting performance. Interestingly, this effect on performance was also observed during control trials of the long pain session in which participants did not receive any painful stimulation. Moreover, subjects expected long painful stimulation to have a greater impact on their performance and individual expectation correlated with working memory performance. These findings suggest that not only the length of painful stimulation but also its expected ability to impair cognitive functioning might influence the interruptive function of pain. The exact relevance of expectation for the detrimental effects of pain on cognitive processes needs to be explored in more detail in future studies.     

Pain Threshold and Arthritis

Pain threshold was measured in 106 patients with rheumatoid arthritis, 50 with ankylosing spondylitis, and 50 normal controls using Keele''s algometer. In rheumatoid arthritis patients with a low pain threshold had more severe pain for a greater part of the day and required more tablets for pain relief. In ankylosing spondylitis the pain threshold was higher and was not related to pain or analgesic requirements. There was no evidence that pain threshold affected the course or outcome of rheumatoid arthritis in any way.     

Origins of Phantom Limb Pain

Phantom limb pain (PLP) is a chronic neuropathic pain occurring in 45–85% of patients who undergo major amputations of the upper and lower extremities. Chronic pain is physically and mentally debilitating, affecting an individual’s potential for self-care and the performance of daily living activities essential for personal and economic independence. In addition, chronic pain may lead to depression and feelings of hopelessness. A National Center for Biotechnology Information study found that in the USA alone, the annual cost of dealing with neuropathic pain is more than $600 billion, with an estimated 20 million people in the USA suffering this condition. PLP manifest predominantly during two time frames post-amputation: during days to a month and again at around 1 year. In most patients, the frequency and intensity of the chronic neuropathic pain diminish over time, but severe pain persists in about 5–10% of patients. The development and maintenance of neuropathic pain is attributed to extremity amputations causing changes in peripheral axon properties and neuronal circuitry in both the peripheral and central nervous systems: peripheral axons, dorsal root ganglia, the spinal cord, and the cortex. However, it is not clear how the changes in neuronal properties in these different locations affect neuropathic pain. Is pain initiated by one set of post-amputation changes while the pain is maintained by another set of changes? If one set of amputation-induced changes, such as those of peripheral axons, are reverted to normal, is the chronic pain reduced or eliminated, while reversing another set of neuronal changes and neuronal circuits to normal do not reduce or eliminate the pain? Or, must all the amputation-induced changes be reverted to normal for pain to be eliminated? While this review examines the mechanisms underlying the induction or maintenance of PLP, it is beyond its scope to examine the mechanisms that may permanently reduce or eliminate neuropathic pain. This paper is the first of two reviews in this journal and deals with the causes of chronic PLP development and maintenance, while the second review examines potential mechanisms that may be responsible for promoting the capacity to coping with PLP by reducing or eliminating it.     

慢性疼痛治疗的研究进展

慢性疼痛是临床常见的病症,给患者和社会都带来极大的负担。其发病机制受生理、心理和社会等多种因素的影响较为复杂,因此,慢性疼痛的治疗一直是临床上的一大难题。单一的治疗手段往往不能取得令人满意的效果,目前常采用多手段联合的方式来治疗慢性疼痛,常见的包括药物治疗、心理治疗、介入治疗以及自我管理等。针对不同类型的慢性疼痛甚至同一类型的不同病人其治疗方案也不尽相同,近年来兴起的跨学科康复计划为慢性疼痛的治疗指明了方向。本文就慢性疼痛治疗的研究进展进行了综述,以期为临床实践提供更多参考和理论依据。