Central pain mechanisms in chronic pain states--maybe it is all in their head

Understanding central mechanisms of acupuncture analgesia using dynamic quantitative sensory testing: a review

We discuss the emerging translational tools for the study of acupuncture analgesia with a focus on psychophysical methods. The gap between animal mechanistic studies and human clinical trials of acupuncture analgesia calls for effective translational tools that bridge neurophysiological data with meaningful clinical outcomes. Temporal summation (TS) and conditioned pain modulation (CPM) are two promising tools yet to be widely utilized. These psychophysical measures capture the state of the ascending facilitation and the descending inhibition of nociceptive transmission, respectively. We review the basic concepts and current methodologies underlying these measures in clinical pain research, and illustrate their application to research on acupuncture analgesia. Finally, we highlight the strengths and limitations of these research methods and make recommendations on future directions. The appropriate addition of TS and CPM to our current research armamentarium will facilitate our efforts to elucidate the central analgesic mechanisms of acupuncture in clinical populations.

Painful effects of auditory startle, forehead cooling and psychological stress in patients with fibromyalgia or rheumatoid arthritis

OBJECTIVE

The aim of this study was to determine whether the clinical pain associated with rheumatoid arthritis or fibromyalgia would increase during standard laboratory tasks and, if so, whether these increases were linked with individual differences in psychological distress.

METHODS

Twenty-three patients with fibromyalgia and 16 patients with rheumatoid arthritis rated changes in clinical pain after an acoustic startle stimulus, during painful forehead cooling, and during stressful mental arithmetic. In addition, pain tolerance was assessed during a submaximal effort tourniquet test, and patients provided ratings of distress on a standard Depression, Anxiety and Stress Inventory.

RESULTS

Pain at rest was associated with depression scores in patients with rheumatoid arthritis, and was associated with stress scores in the fibromyalgia group. However, pain tolerance was unrelated to individual differences in psychological distress in either group. In patients with fibromyalgia, clinical pain increased after the acoustic startle stimulus and painful forehead cooling, and increased during stressful mental arithmetic. Arthritic pain also increased during forehead cooling and mental arithmetic in association with indices of psychological distress.

CONCLUSIONS

These findings suggest that processes linked with individual differences in distress aggravate pain in rheumatoid arthritis, whereas some other mechanism (e.g., failure of stress-related pain modulation processes or an aberrant interaction between nociceptive afferent and sympathetic efferent fibers) triggers stress-induced pain in fibromyalgia.

Chronic pain treatment: the influence of tricyclic antidepressants on serotonin release and uptake in mast cells

The involvement of serotonin (5-HT) in chronic pain mechanisms is established. 5-HT inhibits central painful stimuli, but recent data suggests that 5-HT could also enhance pain stimulus from the periphery, where mast cells play an important role. We aimed in our study to clarify the influence of selected tricyclic antidepressants (TCAs) on mast cell function: secretion, uptake, and reuptake of 5-HT, that could interfere with 5-HT levels and in this way contribute to the generation of pain. As an experimental model, we used isolated rat peritoneal mast cells and incubated them with selected TCAs (clomipramine, amitriptyline, doxepin, and imipramine) under different experimental conditions. 5-HT release, uptake, and reuptake were determined spectrofluorometrically. We showed that TCAs were able to inhibit 5-HT secretion from mast cells, as well as uptake of exogenous 5-HT and reuptake of secreted 5-HT back into mast cells. The effects of TCAs were concentration dependent; higher concentrations of TCAs inhibited the secretion of 5-HT induced by compound 48/80, whereas lower concentrations of TCAs inhibited 5-HT uptake. The most effective TCA was halogenated clomipramine. As TCAs are well introduced in chronic pain treatment, the insight into mechanisms of action is important for an understanding of their effect in various pain conditions.

The multitarget opioid ligand LP1's effects in persistent pain and in primary cell neuronal cultures

Persistent pain states, such as those caused by nerve injury or inflammation, are associated with altered sensations, allodynia and hyperalgesia, that are resistant to traditional analgesics. A contribution to development and maintenance in altered pain perception comes from nociceptive processing and descending modulation from supraspinal sites. A multitarget ligand seems to be useful for pain relief with a decreased risk of adverse events and a considerable analgesic efficacy. The multitarget MOR agonist-DOR antagonist LP1, (3-[(2R,6R,11R)-8-hydroxy-6,11-dimethyl-1,4,5,6-tetrahydro-2,6-methano-3-benazocin-3(2H)-yl]-N-phenylpropanamide, is a central acting antinociceptive agent with low potential to induce tolerance. LP1 was tested in models of neuropathic pain - induced by chronic constriction injury (CCI) of the left sciatic nerve - and inflammatory pain - produced by intraplantar injection of carrageenan. In CCI rats, subcutaneous (s.c.) LP1 (3 mg/kg) showed a significant antiallodynic effect, measured with von Frey filaments, and antihyperalgesic effect, evoked in response to a radiant heat stimulus with plantar test. Analogously, LP1 significantly reduced allodynic and hyperalgesic thresholds in a model of inflammatory pain induced by carrageenan. To evaluate the contribution of opioid receptor subtypes in LP1 antinociceptive effects, the multitarget LP1 profile was assessed using selective opioid antagonists. Moreover, functional electrophysiological in vitro assays, using primary cortical and spinal cord networks, allowed to define the "pharmacological fingerprint" of LP1. The EC₅₀ values in this functional screening seem to confirm LP1 as a potent opioid ligand (EC₅₀ = 0.35 fM and EC₅₀ = 44 pM in spinal cord and frontal cortex, respectively). Using a NeuroProof data-base of well characterised reference compounds, a similarity profile of LP1 to opioid and non-opioid drugs involved in pain modulation was detected. Our studies seem to support that multitarget ligand approach should be useful for persistent pain conditions in which mechanical allodynia and thermal hyperalgesia are significant components of the nociceptive response.

The use of psychotropic drugs in irritable bowel syndrome

INTRODUCTION

Irritable bowel syndrome (IBS), the most common functional gastrointestinal disorder, is manifested by chronic abdominal pain associated with irregular bowel movements. Although not life threatening, IBS is associated with impaired quality of life that ranges from mild to severe.

AREAS COVERED

The pathogenesis of IBS is not completely understood, but involves dysfunction of the "brain-gut axis" including peripheral visceral hypersensitivity and central maladaptive processing of visceral pain input. Stress and concomitant psychopathologies such as somatization, anxiety and depression are thought to play a major role in the development, clinical course and response to treatment. Psychopharmacological agents such as selective serotonin/serotonin-norepinephrine receptor antagonists, tricyclic antidepressants as well as other agents are commonly used in treating moderate to severe IBS. This review will provide the pathophysiological rationale for the use of psychopharmacological agents in IBS, review the main classes of drugs and evidence for their use in IBS and offer a practical approach to the use of these drugs.

EXPERT OPINION

Psychotropic drugs can play a pivotal role in the treatment of IBS patients, so doctors should be familiar with their use. Further research with these drugs is needed to solidify our current knowledge and increase our therapeutic options.

Modulation of the axon-reflex response to local heat by reactive oxygen species in subjects with chronic fatigue syndrome

Local cutaneous heating causes vasodilation as an initial first peak, a nadir, and increase to plateau. Reactive oxygen species (ROS) modulate the heat plateau in healthy controls. The initial peak, due to C-fiber nociceptor-mediated axon reflexes, is blunted with local anesthetics and may serve as a surrogate for the cutaneous response to peripheral heat. Chronic fatigue syndrome (CFS) subjects report increased perception of pain. To determine the role of ROS in this neurally mediated response, we evaluated changes in cutaneous blood flow from local heat in nine CFS subjects (16-22 yr) compared with eight healthy controls (18-26 yr). We heated skin to 42°C and measured local blood flow as a percentage of maximum cutaneous vascular conductance (%CVC(max)). Although CFS subjects had significantly lower baseline flow [8.75 ± 0.56 vs. 12.27 ± 1.07 (%CVC(max), CFS vs. control)], there were no differences between groups to local heat. We then remeasured this with apocynin to inhibit NADPH oxidase, allopurinol to inhibit xanthine oxidase, tempol to inhibit superoxide, and ebselen to reduce H(2)O(2). Apocynin significantly increased baseline blood flow (before heat, 14.91 ± 2.21 vs. 8.75 ± 1.66) and the first heat peak (69.33 ± 3.36 vs. 59.75 ± 2.75). Allopurinol and ebselen only enhanced the first heat peaks (71.55 ± 2.48 vs. 61.72 ± 2.01 and 76.55 ± 5.21 vs. 58.56 ± 3.66, respectively). Tempol had no effect on local heating. None of these agents changed the response to local heat in control subjects. Thus the response to heat may be altered by local levels of ROS, particularly H(2)O(2) in CFS subjects, and may be related to their hyperesthesia/hyperalgesia.

Lifestyle-oriented non-pharmacological treatments for fibromyalgia: a clinical overview and applications with home-based technologies

Fibromyalgia (FM) is a persistent and disabling widespread pain condition often accompanied by chronic fatigue, cognitive problems, sleep disturbance, depression, anxiety, and headache. To date, the most thoroughly studied non-pharmacological approaches to managing FM are those with a focus on changing patient activities and beliefs that affect the illness. These interventions are intended to facilitate enduring improvement in pain and functional status. Lifestyle-oriented treatments include patient education, aerobic or other physical exercise, and cognitive-behavioral therapy (CBT). These interventions in FM can be delivered in medical or behavioral health care settings by trained professionals, through patient-oriented treatment manuals, or via remote-access technologies. Non-pharmacological treatments, in particular exercise and CBT, have yielded effect sizes and cost–benefit ratios comparable to medications. This paper describes lifestyle-oriented non-pharmacological treatments for FM and highlights selected literature reviews of these interventions. In addition, behavioral and practical issues are addressed that may affect these non-pharmacological treatments, including patient expectations, participant burden, and treatment availability. Recommendations are made to facilitate these interventions and potentially improve outcomes. In particular, the increasing availability of convenient home-based mobile technologies to deliver these non-pharmacological treatments is described.

Comorbidities of bladder pain syndrome/interstitial cystitis: a population-based study

Study Type--System prevalence (cohort) Level of Evidence 2a. What's known on the subject? and What does the study add? Compared with the general population, patients with BPS/IC often experience difficulties in performing normal activities owing to physical limitations, decreased energy, greater pain and impaired social functioning With the exception of metastatic cancer, separate conditional logistic regression analyses in this study suggested that subjects with BPS/IC were consistently more likely than subjects without BPS/IC to have all the medical comorbidities investigated. When compared with subjects without BPS/IC, subjects with BPS/IC had particularly higher odds of comorbid neurological diseases, rheumatological diseases and mental illnesses.

OBJECTIVE

• To explore the comorbid medical conditions of patients with bladder pain syndrome/interstitial cystitis (BPS/IC) in Taiwan using a cross-sectional study design and a population-based administrative database.

SUBJECTS AND METHODS

• The study included 9269 subjects with BPS/IC and 46,345 randomly selected comparison subjects. • Conditional logistic regression analyses were performed to calculate the odds ratio for each of the 32 medical comorbidities (hypertension, congestive heart failure, cardiac arrhythmias, blood loss anaemia, peripheral vascular disorders, stroke, ischaemic heart disease, hyperlipidaemia, hepatitis B or C, migraines, headaches, Parkinson's disease, rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis, pulmonary circulation disorders, chronic pulmonary disease, diabetes, hypothyroidism, renal failure, fluid and electrolyte disorders, liver diseases, peptic ulcers, deficiency anaemias, depressive disorder, psychoses, metastatic cancer, solid tumour without metastasis, alcohol abuse, drug abuse and asthma) between subjects with and without BPS/IC.

RESULTS

• With the exception of metastatic cancer, the subjects with BPS/IC had a significantly higher prevalence of all the medical comorbidities analysed than subjects without BPS/IC. • With the exception of metastatic cancer, separate conditional logistic regression analyses suggested that subjects with BPS/IC were consistently more likely than subjects without BPS/IC to have any of the medical comorbidities investigated in this study. • When compared with subjects without BPS/IC, subjects with BPS/IC had particularly higher odds of comorbid neurological diseases, rheumatological diseases and mental illnesses.

CONCLUSION

• Our results indicated that subjects with BPS/IC had an increased prevalence of multiple comorbidities.

[Etiopathogenetic aspects of somatoform disorders]

The etiopathology of somatoform disorders can only be understood against the background of an integrated biopsychosocial model. Cultural and historical influences must be taken into account as well as contemporary settings of scientific or medical priorities. In this context the emphasis on neurobiological findings can be interpreted as the non-accidental struggle for legitimacy of both patients and physicians. Altogether the available data on factors influencing the formation and maintenance of somatoform symptoms has to be described as both diverse and unspecific and thus points to a challenging research program in the coming years.

Cigarette smoking and pain: depressive symptoms mediate smoking-related pain symptoms

Numerous studies have shown an association between smoking and pain, with smokers reporting more pain and worse functioning. However, little is known about factors that impact this complex relationship. This study investigated the association between smoking, pain, and depressive symptoms. Participants were new patients seen at a multidisciplinary pain clinic. All patients were mailed an intake packet of validated questionnaires as part of an ongoing research and clinical care initiative. Of the 497 patients evaluated, 426 had valid smoking data. Among these patients, 32.6% (n = 139) reported being current smokers, 31.7% (n = 135) were classified as former smokers, and 35.7% (n = 152) were never smokers. A multivariate analysis of covariance (smoking status, age, gender, education) revealed a main effect for pain severity (F = 7.36, P<0.001), pain interference (F = 4.03, P = 0.001), and depressive symptoms (F = 7.87, P<0.001). Current smokers demonstrated higher pain severity, pain interference, and depressive symptoms compared with former smokers and never smokers (P<0.01 for all analyses), while there were no differences between the former-smoker and never-smoker groups. However, the effect of smoking on pain severity (P = 0.06) and pain interference (P = 0.22) was no longer significant after controlling for depressive symptoms in a mediation model. Additionally, among former smokers, longer quit duration was associated with less pain severity. In conclusion, smoking rates were high and smoking was associated with a worse chronic pain phenotype. Importantly, depressive symptoms emerged as a critical mediating factor in helping to explain the relationship between smoking and pain.

Chronic widespread pain: from peripheral to central evolution

Chronic pain can be classified as localised, regional or widespread, and its high prevalence in the general population seems to increase with age. The majority of cases present with musculoskeletal pain. The conditions associated with chronic widespread pain (CWP) are highly burdensome as their characteristic symptoms may include multifocal pain, fatigue, insomnia, memory difficulties and a higher rate of concomitant mood disorders. After many years of debate, it is still unclear whether CWP (central sensitisation) is an entirely explainable neurotransmitter-related process or is partially or totally due to individual cognitive experiences and evaluations. The two models (neurochemical and biopsychosocial) also affect our ability to find therapeutic answers.

Migraine and erectile dysfunction: Evidence from a population-based case-control study

Background: This case-control study aimed to estimate the association between erectile dysfunction (ED) and migraines using a nationwide population-based database in Taiwan.

Methods: The data used for this matched case-control study were retrieved from the Taiwan Longitudinal Health Insurance Database 2000. We identified 5763 patients with ED as the cases and randomly selected 17,289 patients as the controls. Conditional logistic regression was used to calculate the odds ratios (OR) for prior migraine between cases and controls.

Results: After adjusting for hypertension, diabetes, hyperlipidaemia, renal disease, coronary heart disease, obesity, and alcohol abuse/alcohol dependence syndrome, conditional logistic regression revealed that among ED patients the odds of having been previously diagnosed with migraines was 1.63 (95% CI, 1.39–1.91) that of the control group. This risk was more pronounced in younger groups, with the highest risk being detected among those aged between 30 and 39 years. After adjusting for the above mentioned comorbidities, ED patients aged between 30 and 39 years were found to be at 1.98 (95% CI, 1.67–2.23) times the risk of controls for having been previously diagnosed with migraines.

Conclusion: We conclude that ED is associated with having been previously diagnosed with migraines, particularly in younger populations.