Abnormal Modulatory Influence of Diffuse Noxious Inhibitory Controls in Migraine and Chronic Tension-Type Headache Patients

Painful heat reveals hyperexcitability of the temporal pole in interictal and ictal migraine States

During migraine attacks, alterations in sensation accompanying headache may manifest as allodynia and enhanced sensitivity to light, sound, and odors. Our objective was to identify physiological changes in cortical regions in migraine patients using painful heat and functional magnetic resonance imaging (fMRI) and the structural basis for such changes using diffusion tensor imaging (DTI). In 11 interictal patients, painful heat threshold + 1°C was applied unilaterally to the forehead during fMRI scanning. Significantly greater activation was identified in the medial temporal lobe in patients relative to healthy subjects, specifically in the anterior temporal pole (TP). In patients, TP showed significantly increased functional connectivity in several brain regions relative to controls, suggesting that TP hyperexcitability may contribute to functional abnormalities in migraine. In 9 healthy subjects, DTI identified white matter connectivity between TP and pulvinar nucleus, which has been related to migraine. In 8 patients, fMRI activation in TP with painful heat was exacerbated during migraine, suggesting that repeated migraines may sensitize TP. This article investigates a nonclassical role of TP in migraineurs. Observed temporal lobe abnormalities may provide a basis for many of the perceptual changes in migraineurs and may serve as a potential interictal biomarker for drug efficacy.

Brain tumor headaches: from bedside to bench

Although most people who have headache pain do not present with an underlying mass lesion, a large number of patients with brain tumors do report headache (as many as 60% in our institution). The problem for clinicians is that the tumor-headache association is not universal, as evidenced by anecdotal reports of patients with large tumors and increased intracranial pressure, but a complete absence of headache pain. In this review, we examine more than 80 years of research on brain tumor headaches, delineating the link between tumor location, laterality, growth rate, and pain. Most importantly, we position our review within the context of current etiological theories and propose new models involving the peripheral and central sensitization of nociresponsive neurons. This review will help clinicians understand why debulking surgery sometimes fails to alleviate neoplastic headache pain in select patients. A brief examination of headaches as a result of surgery and adjuvant chemoradiation therapy is also provided. Headaches can be an early indicator of central nervous system tumors. However, headaches are present in a wide variety of other condition, and are sometimes (surprisingly) absent in patients with primary neoplasms or metastatic tumors. This observation complicates the possibility of linking headaches to brain tumors. Nevertheless, some generalizations concerning brain tumor headaches can be drawn. The following sections review these generalizations, presenting caveats where appropriate. Lingering questions in the field are also addressed and presented together with promising future research avenues.

Stress and tension-type headache mechanisms

Stress is widely demonstrated as a contributing factor in tension-type headache (TTH). The mechanisms underlying this remain unclear at present. Recent research indicates the importance of central pain processes in tension-type headache (TTH) pathophysiology. Concurrently, research with animals and healthy humans has begun to elucidate the relationship between stress and pain processing in the central nervous system, including central pain processes putatively dysfunctional in TTH. Combined, these two fields of research present new insights and hypotheses into possible mechanisms by which stress may contribute to TTH. To date, however, there has been no comprehensive review of this literature. The present paper provides such a review, which may be valuable in facilitating a broader understanding of the central mechanisms by which stress may contribute to TTH.

Treating pain with pain: supraspinal mechanisms of endogenous analgesia elicited by heterotopic noxious conditioning stimulation

While being exposed to an intensive tonic pain stimulus at one area of the body, another phasic pain stimulus applied to a remote site is perceived as less painful. The neurophysiological basis for this "pain inhibits pain" phenomenon has been presumed to be an activation of the spino-bulbo-spinal mechanism termed "diffuse noxious inhibitory controls." However, several additional mechanisms such as an activation of the descending pain control system may contribute to this observation. Here we investigated the underlying supraspinal mechanisms of "heterotopic noxious conditioning stimulations" (HNCS), representing this specific experimental constellation. We used functional magnetic resonance imaging and behavioral recordings in combination with a modified cold-pressor task and phasic painful stimuli, and investigated the contribution of endogenous opioids to this mechanism using the opioid antagonist naloxone in a double-blind crossover design. HNCS led to marked endogenous analgesia and this effect correlated positively with the perceived intensity of the tonic painful stimulus. Furthermore, HNCS was paralleled by reduced blood oxygen level dependent (BOLD) responses in classical pain-responsive regions. Conversely, HNCS led to tonic BOLD increases in subregions of the anterior cingulate cortex. The strength of functional coupling between the subgenual anterior cingulate cortex and key structures of the descending pain control system was enhanced during HNCS, which correlated positively with the individual endogenous analgesia during HNCS. These effects were in part reversed by naloxone, speaking for the contribution of endogenous opioid neurotransmission to this mechanism. Taken together, these results demonstrate a substantial contribution of higher-order brain regions to the phenomenon of hypoalgesia during HNCS. Functional magnetic resonance imaging shows how the human brain is involved in heterotopic noxious conditioning and reveals active supraspinal pain modulatory mechanisms during dual pain stimulation.

Abnormal cortical responses to somatosensory stimulation in medication-overuse headache

BACKGROUND

Medication-overuse headache (MOH) is a frequent, disabling disorder. Despite a controversial pathophysiology convincing evidence attributes a pivotal role to central sensitization. Most patients with MOH initially have episodic migraine without aura (MOA) characterized interictally by an absent amplitude decrease in cortical evoked potentials to repetitive stimuli (habituation deficit), despite a normal initial amplitude (lack of sensitization). Whether central sensitization alters this electrophysiological profile is unknown. We therefore sought differences in somatosensory evoked potential (SEP) sensitization and habituation in patients with MOH and episodic MOA.

METHODS

We recorded median-nerve SEPs (3 blocks of 100 sweeps) in 29 patients with MOH, 64 with MOA and 42 controls. Episodic migraineurs were studied during and between attacks. We measured N20-P25 amplitudes from 3 blocks of 100 sweeps, and assessed sensitization from block 1 amplitude, and habituation from amplitude changes between the 3 sequential blocks.

RESULTS

In episodic migraineurs, interictal SEP amplitudes were normal in block 1, but thereafter failed to habituate. Ictal SEP amplitudes increased in block 1, then habituated normally. Patients with MOH had larger-amplitude block 1 SEPs than controls, and also lacked SEP habituation. SEP amplitudes were smaller in triptan overusers than in patients overusing nonsteroidal anti-inflammatory drugs (NSAIDs) or both medications combined, lowest in patients with the longest migraine history, and highest in those with the longest-lasting headache chronification.

CONCLUSIONS

In patients with MOH, especially those overusing NSAIDs, the somatosensory cortex becomes increasingly sensitized. Sensory sensitization might add to the behavioral sensitization that favors compulsive drug intake, and may reflect drug-induced changes in central serotoninergic transmission.

Facilitated temporal summation of pain at spinal level in Parkinson's disease

BACKGROUND

Pain is one of the major nonmotor symptoms of Parkinson's disease. We hypothesized that Parkinson's disease patients could show an early diffuse abnormal processing of the nociceptive inputs also in the absence of clinical pain syndrome and that this could represent the physiopathological substrate to explain the high incidence of diffuse pain symptoms.

MATERIALS AND METHODS

We used the temporal summation threshold of the nociceptive withdrawal reflex and the related pain sensation to evaluate the facilitation in pain processing at spinal level. Fifteen (7 Women; 8 Men; mean age 63.0 ± 9.1) Parkinson's disease patients without clinical pain and 12 (6 Women, 6 Men; mean age 61.2 ± 4.2) healthy subjects were recruited. Parkinson's disease group has been subdivided into two subgroups, 7 early-stage Parkinson's disease patients with unilateral signs (Hoehn and Yahr stage 1) and 8 patients in a more advanced stage of the disease showing bilateral parkinsonian signs (Hoehn and Yahr stages 2 and 2.5), both "on" and "off" treatments with levodopa.

RESULTS

A significant facilitation in temporal summation of pain (reduced temporal summation threshold and increased painful sensation) was found in Parkinson's disease patients when compared with controls. This facilitation is more evident in Parkinson's disease with bilateral signs and on the side more affected in Parkinson's disease with unilateral signs. Levodopa administration failed to significantly modify the neurophysiological abnormalities; however, a slight improvement has been detected.

CONCLUSIONS

The increased gain in pain processing at spinal level in Parkinson's disease patients could be a consequence of the degenerative phenomena involving supraspinal projections implicated in the modulation of pain processing and could make Parkinson's disease patients more predisposed to develop a pain condition.

Pain perception studies in tension-type headache

Tension-type headache (TTH) is a disorder with high prevalence and significant impact on society. Understanding of pathophysiology of TTH is paramount for development of effective treatments and prevention of chronification of TTH. Our aim was to review the findings from pain perception studies of pathophysiology of TTH as well as to review the research of pathophysiology of TTH. Pain perception studies such as measurement of muscle tenderness, pain detection thresholds, pain tolerance thresholds, pain response to suprathreshold stimulation, temporal summation and diffuse noxious inhibitory control (DNIC) have played a central role in elucidating the pathophysiology of TTH. It has been demonstrated that continuous nociceptive input from peripheral myofascial structures may induce central sensitization and thereby chronification of the headache. Measurements of pain tolerance thresholds and suprathreshold stimulation have shown presence of generalized hyperalgesia in chronic tension-type headache (CTTH) patients, while DNIC function has been shown to be reduced in CTTH. One imaging study showed loss of gray matter structures involved in pain processing in CTTH patients. Future studies should aim to integrate pain perception and imaging to confirm this finding. Pharmacological studies have shown that drugs like tricyclic anti-depressant amitriptyline and nitric oxide synthase inhibitors can reverse central sensitization and the chronicity of headache. Finally, low frequency electrical stimulation has been shown to rapidly reverse central sensitization and may be a new modality in treatment of CTTH and other chronic pain disorders.

Neurophysiological tests and neuroimaging procedures in non-acute headache (2nd edition)

BACKGROUND AND PURPOSE

A large number of instrumental investigations are used in patients with non-acute headache in both research and clinical fields. Although the literature has shown that most of these tools contributed greatly to increasing understanding of the pathogenesis of primary headache, they are of little or no value in the clinical setting.

METHODS

This paper provides an update of the 2004 EFNS guidelines and recommendations for the use of neurophysiological tools and neuroimaging procedures in non-acute headache (first edition). Even though the period since the publication of the first edition has seen an increase in the number of published papers dealing with this topic, the updated guidelines contain only minimal changes in the levels of evidence and grades of recommendation.

RESULTS

(i) Interictal EEG is not routinely indicated in the diagnostic evaluation of patients with headache. Interictal EEG is, however, indicated if the clinical history suggests a possible diagnosis of epilepsy (differential diagnosis). Ictal EEG could be useful in certain patients suffering from hemiplegic or basilar migraine. (ii) Recording evoked potentials is not recommended for the diagnosis of headache disorders. (iii) There is no evidence warranting recommendation of reflex responses or autonomic tests for the routine clinical examination of patients with headache. (iv) Manual palpation of pericranial muscles, with standardized palpation pressure, can be recommended for subdividing patient groups but not for diagnosis. Pain threshold measurements and EMG are not recommended as clinical diagnostic tests. (v) In adult and pediatric patients with migraine, with no recent change in attack pattern, no history of seizures, and no other focal neurological symptoms or signs, the routine use of neuroimaging is not warranted. In patients with trigeminal autonomic cephalalgia, neuroimaging should be carefully considered and may necessitate additional scanning of intracranial/cervical vasculature and/or the sellar/orbital/(para)nasal region. In patients with atypical headache patterns, a history of seizures and/or focal neurological symptoms or signs, MRI may be indicated. (vi) If attacks can be fully accounted for by the standard headache classification (IHS), a PET or SPECT scan will normally be of no further diagnostic value. Nuclear medical examinations of the cerebral circulation and metabolism can be carried out in subgroups of patients with headache for the diagnosis and evaluation of complications, when patients experience unusually severe attacks or when the quality or severity of attacks has changed. (vii) Transcranial Doppler examination is not helpful in headache diagnosis.

CONCLUSION

Although many of the examinations described in the present guidelines are of little or no value in the clinical setting, most of the tools, including thermal pain thresholds and transcranial magnetic stimulation, have considerable potential for differential diagnostic evaluation as well as for the further exploration of headache pathophysiology and the effects of pharmacological treatment.

Generalized mechanical nerve pain hypersensitivity in children with episodic tension-type headache

OBJECTIVES

The objective of this study was to analyze the presence of generalized pressure pain hypersensitivity over nerve tissues in trigeminal and nontrigeminal regions in children with frequent episodic tension-type headache (FETTH).

METHODS

Thirty children, 7 boys and 23 girls (mean age: 8.8 +/- 1.7 years) with FETTH and 50 age- and gender-matched healthy children (14 boys, 36 girls; mean age: 8.5 +/- 2.1 years; P = .743) were recruited. Pressure pain thresholds (PPTs) were bilaterally assessed over supra-orbital (V1), infra-orbital (V2), mental (V3), median (C5), radial (C6), and ulnar (C7) nerves by an assessor who was blinded to the patient's condition.

RESULTS

The analysis of variance showed that PPT levels were significantly bilaterally decreased over both trigeminal (supra-orbital, infra-orbital, and mental) and nontrigeminal (median, ulnar, and radial) nerves in children with FETTH as compared with control subjects (all sites, P < .001). There was a greater magnitude of PPT decrease within trigeminal nerves as compared with nontrigeminal nerves (P < .03). PPTs over infra-orbital (r(s) = -0.4, P < .05) and radial (r(s) = -0.5, P < .01) nerves were negatively correlated with the duration of headache attacks (P < .05).

CONCLUSIONS

Our study revealed bilateral and generalized pressure hypersensitivity over both trigeminal and nontrigeminal nerves in children with FETTH. Diffuse hypersensitivity of peripheral nerves evidences the presence of hyperexcitability of the central nervous system in children with FETTH.

Bilateral, wide-spread, mechanical pain sensitivity in children with frequent episodic tension-type headache suggesting impairment in central nociceptive processing

Introduction: The aim was to investigate bilateral, wide-spread pressure pain hyperalgesia in symptomatic (trigeminocervical) and non-symptomatic (pain-free distant) regions in children with frequent episodic tension-type headache (FETTH).

Methods: Twenty-five children, 6 boys and 19 girls (mean age, 8.9 ± 1.8 years) with FETTH and 50 age- and sex-matched healthy children (12 boys, 38 girls; mean age: 8.8 ± 1.7 years) were recruited. Pressure pain thresholds (PPTs) were bilaterally assessed over temporalis muscle, upper trapezius muscle, second metacarpal and tibialis anterior muscles in a blinded design.

Results: The results showed that PPT levels were significantly decreased bilaterally over the temporalis, upper trapezius and tibialis muscles, and the second metacarpal in children with FETTH as compared to controls (all sites, P < 0.001). No significant differences in the magnitude of PPT decrease between the upper trapezius muscle, second metacarpal and tibialis anterior muscles were found. PPT over both upper trapezius muscles were negatively correlated with the history and intensity of headache (rs = −0.415; P = 0.045).

Conclusions: The findings revealed bilateral, wide-spread pressure pain hypersensitivity in children with FETTH suggesting that wide-spread central sensitisation is involved in children with this headache pain condition.

Neonatal bladder inflammation alters activity of adult rat spinal visceral nociceptive neurons

PURPOSE

This investigation examined the effect of inflammation produced by intravesical zymosan during the neonatal period on spinal dorsal horn neuronal responses to urinary bladder distension (UBD) as adults.

METHODS

Female rat pups (P14-P16) were treated with intravesical zymosan or with anesthesia-only. These groups of rats were subdivided forming four groups: half received intravesical zymosan as adults and half received anesthesia-only. One day later, rats were anesthetized, the spinal cord was transected at a cervical level and extracellular single-unit recordings of L6-S1 dorsal horn neurons were obtained. Neurons were classified as Type I--inhibited by heterotopic noxious conditioning stimuli (HNCS) or as Type II--not inhibited by HNCS--and were characterized for Spontaneous Activity and responses to graded UBD (20-60 mm Hg).

RESULTS

227 spinal dorsal horn neurons excited by UBD were characterized. In rats treated as neonates with anesthesia-only, Type II neurons demonstrated increased spontaneous and UBD-evoked activity following adult intravesical zymosan treatment whereas Type I neurons demonstrated decreased spontaneous and UBD-evoked activity relative to controls. In rats treated as neonates with intravesical zymosan, the spontaneous and UBD-evoked activity of both Type I and Type II neurons increased following adult intravesical zymosan treatment relative to controls.

CONCLUSIONS

Neonatal bladder inflammation alters subsequent effects of acute bladder inflammation on spinal dorsal horn neurons excited by UBD such that overall there is greater sensory neuron activation. This may explain the visceral hypersensitivity noted in this model system and suggest that impaired inhibitory systems may be responsible.

Low-frequency electrical stimulation induces long-term depression in patients with chronic tension-type headache

Repetitive low-frequency electrical stimulation (LFS) induces pain inhibition in healthy volunteers and in animals, but it is unknown whether it has an analgesic effect in patients with headache. The aim of this study was to investigate if LFS could induce prolonged pain inhibition, called long-term depression (LTD), in patients with chronic tension-type headache (CTTH). Twenty CTTH patients and 20 healthy volunteers were exposed to 20 min LFS (1 Hz) to the forehead. LTD was measured as a decrease in pain response to electrical stimulation in a 1-h post-LFS period following LFS. The LFS induced a significant and stable inhibition of pain (LTD) both in patients with CTTH (post-LFS average decrease in pain rating: 19.6 +/- 3.9%, all P < 0.005, Holm-Sidak) and in healthy controls (30.1 +/- 5.0%, all P < 0.001, Holm-Sidak). During the LFS period, the pain ratings decreased consistently in both groups. In conclusion, a significant and stable pain inhibition (LTD) can be induced in CTTH patients by LFS.

Central processing of noxious somatic stimuli in patients with irritable bowel syndrome compared with healthy controls

OBJECTIVE

To compare a central analgesic mechanism known as diffuse noxious inhibitory controls (DNIC) using somatic test stimuli and somatic conditioning stimuli, (CS) in irritable bowel syndrome (IBS) patients and healthy controls.

METHODS

Participants were 48 premenopausal females (27 with IBS), mean age of 29 years. The phasic heat test stimulus (peak temperature, 50 degrees C) was applied to the left palm. The DNIC effect, which measured reductions in average pain ratings (APR) during counter irritation (submersion of the participant's right hand in painful 12 degrees C circulating water) compared with baseline, was compared between groups. In addition, a second, counterbalanced, CS protocol (right hand submerged in nonpainful 32 degrees C circulating water) was performed. Differences in APR between the 2 counterirritation protocols were compared between groups to control for nonspecific effects known to influence DNIC. Psychologic measures and cardiovascular reactivity were also assessed.

RESULTS

IBS patients demonstrated smaller DNIC than controls (P=0.011, repeated measures analysis of variance), and greater state-anxiety, depression, catastrophizing, and anger-out expression (P<0.05). Group differences in DNIC were enhanced after controlling for nonspecific effects occurring during the nonpainful CS, and for psychologic measures (P=0.001, repeated measures analysis of covariance). There were no group differences in age, cardiovascular reactivity, APR, or pain ratings for the 12 degrees C CS.

DISCUSSION

These data demonstrate deficient DNIC in IBS. This is the first study to adequately control for alternative explanations of pain reduction during counterirritation. Only by controlling for nonspecific effects can evidence of deficient DNIC be attributed to dysregulation in endogenous analgesic mechanisms.

How neuroimaging studies have challenged us to rethink: is chronic pain a disease?

In this review, we present data from functional, structural, and molecular imaging studies in patients and animals supporting the notion that it might be time to reconsider chronic pain as a disease. Across a range of chronic pain conditions, similar observations have been made regarding changes in structure and function within the brains of patients. We discuss these observations within the framework of the current definition of a disease.

PERSPECTIVE

Neuroimaging studies have made a significant scientific impact in the study of pain. Knowledge of nociceptive processing in the noninjured and injured central nervous system has grown considerably over the past 2 decades. This review examines the information from these functional, structural, and molecular studies within the framework of a disease state.

The clinical neurophysiology of tension-type headache

Despite being widely investigated, the pathogenesis of tension-type headache (TTH) continues to be debated. Among the different approaches used to explore the mechanisms underlying TTH, clinical neurophysiology plays an important role. Studies to date have focused mainly on two areas: (1) evaluation of peripheral factors (i.e., by electromyography (EMG)); and (2) exploration of the role of the pain control system. In the second of these areas, a large number of studies have explored trigeminal pathways, in particular using reflexes (e.g., the trigeminofacial reflex, trigeminotrigeminal reflexes). More recently, the descending inhibitory system, known to modulate both the trigeminal and the spinal system, has also been investigated. In addition, several studies have sought to establish whether there are neurophysiological parameters that could be markers of this condition, but the results of these were inconclusive, since some abnormalities could frequently be observed in migraine too. This chapter critically reviews the clinical neurophysiology of TTH. It concludes that the majority of neurophysiological studies on TTH present serious methodological flaws that will have to be overcome to allow further understanding of the mechanisms of TTH.

Tonic pain abolishes cortical habituation of visual evoked potentials in healthy subjects

We investigated changes in visual cortex excitability by analyzing visual evoked potential (VEP) habituation in healthy subjects during tonic pain evoked by the cold-pressor test (CPT). We tested VEP amplitude habituation (slope of the linear regression line for N1-P1 amplitude from the 1st to 6th block of 100 sweeps) in 19 healthy volunteers during 4 experimental conditions: baseline; no-pain (hand held in warm water, 25 degrees C); pain (hand held in cold water, 2-4 degrees C); and the after-effects of tonic pain. During baseline and no-pain sessions, VEPs habituated normally across the 6 consecutive blocks (mean slope -.28 and -.18%), whereas during pain and its after-effects they failed to decrease (0%, and -.11%). Tonic pain induced by the CPT abolishes normal VEP habituation and the lack of habituation persists after the CPT is stopped. Tonic pain probably abolishes VEP habituation by acting on brainstem neural structures which modulate thalamo-cortical activation thereby changing visual cortex excitability.

PERSPECTIVE

This study shows that tonic pain alters visual cortex excitability, a brain region unrelated to pain processing. These changes probably reflect defensive strategies against pain. Extending the study from healthy volunteers to patients with migraine between attacks would offer the opportunity to investigate visual cortical excitability under conditions when baseline habituation is absent.

Lack of cold pressor test-induced effect on visual-evoked potentials in migraine

In patients with migraine, the various sensory stimulation modalities, including visual stimuli, invariably fail to elicit the normal response habituation. Whether this lack of habituation depends on abnormal activity in the sub-cortical structures responsible for processing incoming information as well as nociception and antinociception or on abnormal cortical excitability per se remains debateable. To find out whether inducing tonic pain in the hand by cold pressure test (CPT) alters the lack of visual-evoked potential (VEP) habituation in migraineurs without aura studied between attacks we recorded VEPs in 19 healthy subjects and in 12 migraine patients during four experimental conditions: baseline; no-pain (hand held in warm water, 25°C); pain (hand held in cold water, 2–4°C); and after-effects. We measured P100 amplitudes from six blocks of 100 sweeps, and assessed habituation from amplitude changes between the six sequential blocks. In healthy subjects, the CPT decreased block 1 VEP amplitude and abolished the normal VEP habituation (amplitude decrease to repeated stimulation) in patients with migraine studied between attacks; it left block 1 VEP amplitude and abnormal VEP habituation unchanged. These findings suggest that the interictal cortical dysfunction induced by migraine prevents the cortical changes induced by tonic painful stimulation both during pain and after pain ends. Because such cortical changes presumably reflect plasticity mechanisms in the stimulated cortex, our study suggests altered plasticity of sensory cortices in migraine. Whether this abnormality reflects abnormal functional activity in the subcortical structures subserving tonic pain activation remains conjectural.

Reliability of temporal summation and diffuse noxious inhibitory control

BACKGROUND

The test-retest reliability of temporal summation (TS) and diffuse noxious inhibitory control (DNIC) has not been reported to date. Establishing such reliability would support the possibility of future experimental studies examining factors affecting TS and DNIC. Similarly, the use of manual algometry to induce TS, or an occlusion cuff to induce DNIC of TS to mechanical stimuli, has not been reported to date. Such devices may offer a simpler method than current techniques for inducing TS and DNIC, affording assessment at more anatomical locations and in more varied research settings.

METHOD

The present study assessed the test-retest reliability of TS and DNIC using the above techniques. Sex differences on these measures were also investigated.

RESULTS

Repeated measures ANOVA indicated successful induction of TS and DNIC, with no significant differences across test-retest occasions. Sex effects were not significant for any measure or interaction. Intraclass correlations indicated high test-retest reliability for all measures; however, there was large interindividual variation between test and retest measurements.

CONCLUSION

The present results indicate acceptable within-session test-retest reliability of TS and DNIC. The results support the possibility of future experimental studies examining factors affecting TS and DNIC.

Noxious inhibition of temporal summation is impaired in chronic tension-type headache

OBJECTIVE

To examine effects of stress on noxious inhibition and temporal summation (TS) in tension-type headache.

BACKGROUND

Stress is the most commonly reported trigger of a chronic tension-type headache (CTH) episode; however, the mechanisms underlying this are unclear. Stress affects pain processing throughout the central nervous system, including, potentially, mechanisms of TS and diffuse noxious inhibitory controls (DNIC), both of which may be abnormal in CTH sufferers (CTH-S). No studies have examined TS of pressure pain or DNIC of TS in CTH-S to date. Similarly, effects of stress on TS or DNIC of TS have not been reported in healthy subjects or CTH-S to date.

METHODS

The present study measured TS and DNIC of TS in CTH-S and healthy controls (CNT) exposed to an hour-long stressful mental task, and in CTH-S exposed to an hour-long neutral condition. TS was elicited at finger and shoulder via 10 pulses from a pressure algometer, applied before and during stimulation from an occlusion cuff at painful intensity.

RESULTS

Algometer pain ratings increased more in the CTH compared with the CNT group, and were inhibited during occlusion cuff more in the CNT compared with CTH groups. Task effects on TS or DNIC were not significant.

CONCLUSIONS

The results indicate increased TS to pressure pain and impaired DNIC of TS in CTH-S. Stress does not appear to aggravate abnormal TS or DNIC mechanisms in CTH-S.

Psychophysical and functional imaging evidence supporting the presence of central sensitization in a cohort of osteoarthritis patients

OBJECTIVE

The groin pain experienced by patients with hip osteoarthritis (OA) is often accompanied by areas of referred pain and changes in skin sensitivity. We aimed to identify the supraspinal influences that underlie these clinical manifestations that we consider indicative of possible central sensitization.

METHODS

Twenty patients with hip OA awaiting joint replacement and displaying signs of referred pain were recruited into the study, together with age-matched controls. All subjects completed pain psychology questionnaires and underwent quantitative sensory testing (QST) in their area of referred pain. Twelve of 20 patients and their age- and sex-matched controls underwent functional magnetic resonance imaging (MRI) while the areas of referred pain were stimulated using cold stimuli (12 degrees C) and punctate stimuli (256 mN). The remaining 8 of 20 patients underwent punctate stimulation only.

RESULTS

Patients were found to have significantly lower threshold perception to punctate stimuli and were hyperalgesic to the noxious punctate stimulus in their areas of referred pain. Functional brain imaging illustrated significantly greater activation in the brainstem of OA patients in response to punctate stimulation of their referred pain areas compared with healthy controls, and the magnitude of this activation positively correlated with the extent of neuropathic-like elements to the patient's pain, as indicated by the PainDETECT score.

DISCUSSION

Using psychophysical (QST) and brain imaging methods (functional MRI), we have identified increased activity with the periaqueductal grey matter associated with stimulation of the skin in referred pain areas of patients with hip OA. This offers a central target for analgesia aimed at improving the treatment of this largely peripheral disease.

Sensitisation of spinal cord pain processing in medication overuse headache involves supraspinal pain control

Medication overuse could interfere with the activity of critical brain regions involved in the supraspinal control of pain signals at the trigeminal and spinal level, leading to a sensitisation phenomenon responsible for chronic pain. We hypothesised that medication-overuse headache (MOH) patients might display abnormal processing of pain stimuli at the spinal level and defective functioning of the diffuse noxious inhibitory controls. We tested 31 MOH patients before (bWT) and after (aWT) standard inpatient withdrawal treatment, 28 episodic migraine (EM) patients and 23 healthy control subjects. We measured the threshold, the area and the temporal summation threshold (TST) of the nociceptive withdrawal reflex before, during and after activation of the diffuse noxious inhibitory controls by means of the cold pressor test. A significantly lower TST was found in both the MOH (bWT and aWT) and the EM patients compared with the controls, and in the MOH patients bWT compared with both the MOH patients aWT and the EM patients. In the MOH bWT patients the cold pressor test induced a TST increase significantly lower than that found in the MOH aWT, EM and control groups. Abnormal spinal cord pain processing and a decrease of the antinociceptive activity of the supraspinal structures in MOH patients can be hypothesised. These abnormalities could, in part, be related to the medication overuse, given that the withdrawal treatment was related to an improvement in the neurophysiological findings.

Tension-type headache

The substantial societal and individual burdens associated with tension-type headache (TTH) constitute a previously overlooked major public health issue. TTH is prevalent, affecting up to 78% of the general population, and 3% suffer from chronic TTH. Pericranial myofascial nociception probably is important for the pathophysiology of episodic TTH, whereas sensitization of central nociceptive pathways seems responsible for the conversion of episodic to chronic TTH. Headache-related disability usually can be reduced by identification of trigger factors combined with nonpharmacologic and pharmacologic treatments, but effective treatment modalities are lacking. Benefits can be gained by development of specific and effective treatment strategies.

Chronic tension-type headache: what is new?

PURPOSE OF REVIEW

This review discusses current data on nosological boundaries related to diagnosis, pathophysiology and therapeutic strategies in chronic tension-type headache (CTTH).

RECENT FINDINGS

Diagnostic criteria of CTTH should be adapted to improve its sensitivity against migraine. It seems that mechanical pain sensitivity is a consequence and not a causative factor of CTTH. Recent evidence is modifying previous knowledge about relationships between muscle tissues and CTTH, suggesting a potential role of muscle trigger points in the genesis of pain. An updated pain model suggests that headache perception can be explained by referred pain from trigger points in the craniocervical muscles, mediated through the spinal cord and the trigeminal nucleus caudalis rather than only tenderness of the muscles themselves. Different therapeutic strategies, pharmacological, physical therapy, psychological and acupuncture, are generally used. The therapeutic efficacy of nonsteroidal anti-inflammatory drugs remains incomplete. The tricyclic antidepressants are the most used first-line therapeutic agents for CTTH. Surprisingly, few controlled studies have been performed and not all of them have found an efficacy superior to placebo. Further, there is insufficient evidence to support/refute the efficacy of physical therapy in CTTH.

SUMMARY

Although there is an increasing scientific interest in CTTH, future studies incorporating subgroups of patients who will likely to benefit from a specific treatment (clinical prediction rules) should be conducted.

Effect of mental stress on cold pain in chronic tension-type headache sufferers

Mental stress is a noted contributing factor in chronic tension-type headache (CTH), however the mechanisms underlying this are not clearly understood. One proposition is that stress aggravates already increased pain sensitivity in CTH sufferers. This hypothesis could be partially tested by examining effects of mental stress on threshold and supra-threshold experimental pain processing in CTH sufferers. Such studies have not been reported to date. The present study measured pain detection and tolerance thresholds and ratings of supra-threshold pain stimulation from cold pressor test in CTH sufferers (CTH-S) and healthy Control (CNT) subjects exposed to a 60-min stressful mental task, and in CTH sufferers exposed to a 60-min neutral condition (CTH-N). Headache sufferers had lower pain tolerance thresholds and increased pain intensity ratings compared to controls. Pain detection and tolerance thresholds decreased and pain intensity ratings increased during the stress task, with a greater reduction in pain detection threshold and increase in pain intensity ratings in the CTH-S compared to CNT group. The results support the hypothesis that mental stress contributes to CTH through aggravating already increased pain sensitivity in CTH sufferers.

Deficiency in endogenous modulation of prolonged heat pain in patients with Irritable Bowel Syndrome and Temporomandibular Disorder

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 such as 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 degrees C), which was applied to left palm, was continuously rated during three 30-s 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 degrees C (control); and during noxious cold immersion in a (DNIC; 8.0-16.0 degrees C) water bath. Compared to controls, IBS and TMD patients reported an 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 but also demonstrate reduced pain inhibition by pain, possibly because of dysfunction of endogenous pain inhibition systems.

Experimental muscle pain impairs descending inhibition

In chronic musculoskeletal pain conditions, the balance between supraspinal facilitation and inhibition of pain shifts towards an overall decrease in inhibition. Application of a tonic painful stimulus results in activation of diffuse noxious inhibitory controls (DNIC). The aims of the present experimental human study were (1) to compare DNIC, evoked separately, by hypertonic saline (6%)-induced muscle pain (tibialis anterior) or cold pressor pain; (2) to investigate DNIC evoked by concomitant experimental muscle pain and cold pressor pain, and (3) to analyze for gender differences. Ten males and 10 age matched females participated in two sessions. In the first session unilateral muscle pain or unilateral cold pressor pain were induced separately; in the second session unilateral muscle pain and unilateral cold pressor pain were induced concomitantly. Pressure pain thresholds (PPT) were measured around the knee joint before, during, and after DNIC induction. Cold pressor pain increased PPT in both males and females with greater increases in males. Hypertonic saline-evoked muscle pain significantly increased PPT in males but not in females. When cold pressor and muscle pain were applied concomitantly the PPT increases were smaller when compared to the individual sessions. This study showed for the first time that two concurrent conditioning tonic pain stimuli (muscle pain and cold pressor pain) cause less DNIC compared with either of the conditioning stimuli given alone; and males showed greater DNIC than females. This may explain why patients with chronic musculoskeletal pain have impaired DNIC.

Evidence of persistent central sensitization in chronic headaches: a multi-method study

The aim of this study was to investigate central sensitization (CS) in chronic headaches and compare this phenomenon between chronic migraine (CM) and chronic tension-type headache (CTTH). We recruited 69 patients with chronic headaches and 18 control subjects. Questionnaires of headache history, allodynia and the Hospital Anxiety and Depression scale were administered. We recorded thresholds for pinprick and pressure pain, blink (BR) and nociceptive flexion reflex (NFR) R3 component coupled with wind-up ratios. Thresholds for pressure and pinprick pain, BR and NFR R3 were lower and wind-up ratios higher in patients. No differences of CS parameters between CM and CTTH were observed. CS is persistent and prevalent in patients with various types of chronic headache. CS levels are unrelated to the predominant side of pain, disease duration or depression. Neither is CS related to the headache type, suggesting similar mechanisms of headache chronification and chronicity maintaining and possibly explaining clinical similarity of various forms of chronic headache.

Supraspinal modulation of trigeminal nociception and pain

OBJECTIVE

This study examined modulation of trigeminal pain/nociception by 2 supraspinal mechanisms: emotional controls of nociception and diffuse noxious inhibitory controls.

BACKGROUND

Prior research suggests emotional picture viewing (emotional controls) and tonic noxious stimuli (diffuse noxious inhibitory controls) engage supraspinal mechanisms to modulate pain and nociceptive processes. It is currently unknown, however, whether emotional controls modulate trigeminal pain and nociception. Additionally, the influences of emotional controls and diffuse noxious inhibitory controls have not been compared in the same group of participants.

METHODS

Noxious electrodermal stimuli were delivered to the trigeminal nerve using a concentric electrode designed to selectively activate nociceptive fibers. Trigeminal nociception and pain were assessed (34 participants) from the nociceptive blink reflex and pain ratings, respectively. Emotional controls were engaged by presentation of standardized picture stimuli (pleasant, neutral, and unpleasant) shown to reliably evoke pleasure-induced inhibition and displeasure-induced facilitation of pain and nociception. Diffuse noxious inhibitory controls were engaged with a forearm ischemia task.

RESULTS

Trigeminal pain (self-report ratings) and nociception (blinks) were facilitated by unpleasant pictures and inhibited by pleasant pictures. Emotion induction (as assessed from trend analysis) explained 51% of the variance in trigeminal pain and 25% of the variance in trigeminal nociception. Additionally, forearm ischemia inhibited trigeminal pain but not nociception. The baseline vs ischemia comparison explained 17% of the variance in pain report and 0.1% of the variance in blinks. Supraspinal modulation by emotional controls and diffuse noxious inhibitory controls were uncorrelated.

CONCLUSIONS

Emotional controls and diffuse noxious inhibitory controls modulated trigeminal pain and emotional controls modulated trigeminal nociception. These procedures can be used to study supraspinal modulation of nociceptive processing in disorders of the trigeminal pain system, including headache.

Diffuse noxious inhibitory controls triggered by heterotopic CO2 laser conditioning stimulation decreased the SEP amplitudes induced by electrical tooth stimulation with different intensity at an equally inhibitory rate

The purpose of this study was to investigate (1) whether selective Adelta-fiber stimulation with CO(2) laser produces a diffuse noxious inhibitory controls (DNIC) effect in the trigeminal nerve territory; and (2) whether the DNIC effect differs depending on test stimulus intensities under constant conditioning stimuli. To examine whether the CO(2) laser radiation on the dorsum of the hand selectively stimulates Adelta-fibers, laser evoked potentials (LEP) were recorded. The mean peak latency of LEP was 381.4 ms. The findings revealed that the CO(2) laser selectively stimulated Adelta-fibers. Electrical tooth stimuli with 3 levels of intensities (1.2, 1.4, 1.6 times the pain threshold) were applied to subjects as test stimulation in randomized order, with a CO(2) laser stimulus of 18 mJ/mm(2) applied to the dorsum of the hand for 4 min as the noxious conditioning stimulus. Somatosensory evoked potentials (SEP) induced by electrical tooth stimulation were recorded and tooth pain intensity was evaluated using a visual analogue scale (VAS). The amplitudes of the SEP late component and VAS values were significantly decreased only during the conditioning stimuli without aftereffect. The inhibitory rates of the amplitudes ranged from 31.3% to 34.6% and the VAS values from 29.0% to 31.2%. There were no significant differences in their inhibitory rates between the 3 test stimulus intensities. The result indicated that selective Adelta-fiber stimulation with the CO(2) laser produces a DNIC effect in the trigeminal nerve territory and suggested that the DNIC effect does not depend on the intensity of the test stimuli.

Determinants of endogenous analgesia magnitude in a diffuse noxious inhibitory control (DNIC) paradigm: Do conditioning stimulus painfulness, gender and personality variables matter?

Descending modulation of pain can be demonstrated psychophysically by dual pain stimulation. This study evaluates in 31 healthy subjects the association between parameters of the conditioning stimulus, gender and personality, and the endogenous analgesia (EA) extent assessed by diffuse noxious inhibitory control (DNIC) paradigm. Contact heat pain was applied as the test stimulus to the non-dominant forearm, with stimulation temperature at a psychophysical intensity score of 60 on a 0-100 numerical pain scale. The conditioning stimulus was a 60s immersion of the dominant hand in cold (12, 15, 18 degrees C), hot (44 and 46.5 degrees C), or skin temperature (33 degrees C) water. The test stimulus was repeated on the non-dominant hand during the last 30s of the conditioning immersion. EA extent was calculated as the difference between pain scores of the two test stimuli. State and trait anxiety and pain catastrophizing scores were assessed prior to stimulation. EA was induced only for the pain-generating conditioning stimuli at 46.5 degrees C (p=0.011) and 12 degrees C (p=0.003). EA was independent of conditioning pain modality, or personality, but a significant gender effect was found, with greater EA response in males. Importantly, pain scores of the conditioning stimuli were not correlated with EA extent. The latter is based on both our study population, and on additional 82 patients, who participated in another study, in which EA was induced by immersion at 46.5 degrees C. DNIC testing, thus, seems to be relatively independent of the stimulation conditions, making it an easy to apply tool, suitable for wide range applications in pain psychophysics.

Effects of induced stress on experimental pain sensitivity in chronic tension-type headache sufferers

BACKGROUND AND PURPOSE

It has been proposed that stress may contribute to chronic tension-type headache (CTH) through hyperalgesic effects on already sensitized pain pathways in CTH sufferers. This hypothesis could be partially tested by examining effects of stress on mechanical and thermal pain sensitivity in CTH sufferers. Such examinations have not been reported to date.

MATERIALS AND METHODS

In the present study, we measured cephalic and extra-cephalic pressure [pressure-pain threshold (PPT)] and cold-pain thresholds (CPT) in CTH sufferers (n = 8 females, n = 8 males) and healthy control subjects (n = 8 males, n = 7 females) recruited from the general population before and after exposure to a 15-min stressful mental task.

RESULTS

Results indicated that PPT's at head and hand were lower in the CTH compared with control group both before and after task exposure. PPT's and CPT's decreased from pre- to post-task in both groups, with a significantly greater pre- to post-task reduction in cephalic PPT in the CTH compared with control group. Subjective stress increased from pre- to post-task in both groups and did not differ between groups. In the CTH group, stress reactivity was negatively correlated with PPT's, whilst absolute stress levels were positively correlated with pre- to post-task decrease in PPT's.

CONCLUSIONS

The main finding is an enhanced hyperalgesic effect of stress on cephalic pressure-pain sensitivity in the CTH sufferers compared with the healthy controls. The results support the hypothesis that stress may contribute to CTH through hyperalgesic effects on already sensitized pain pathways in CTH sufferers.

Tension-type headache: current research and clinical management

Tension-type headache (TTH) is the most common form of headache, and chronic tension-type headache (CTTH) is one of the most neglected and difficult types of headache to treat. The pathogenesis of TTH is multifactorial and varies between forms and individuals. Peripheral mechanisms (myofascial nociception) and central mechanisms (sensitisation and inadequate endogenous pain control) are intermingled: the former predominate in infrequent and frequent TTH, whereas the latter predominate in CTTH. Acute therapy is effective for episodes of TTH, whereas preventive treatment--which is indicated for frequent and chronic TTH--is, on average, not effective. For most patients with CTTH, the combination of drug therapies and non-drug therapies (such as relaxation and stress management techniques or physical therapies) is recommended. There is clearly an urgent need to improve the management of patients who are disabled by headache. This Review summarises the present knowledge on TTH and discusses some of its more problematic features.

The influence of pain catastrophizing on experimentally induced emotion and emotional modulation of nociception

Pain catastrophizing is associated with enhanced pain and pain-related outcomes. Unfortunately, the mechanisms underlying the catastrophizing-pain relationship are poorly understood. Given evidence suggesting significant relationships among catastrophizing, emotion, and pain, it is possible that catastrophizing may alter nociception and pain through affective processes. Research has shown that emotionally charged pictures (erotica, neutral, threat/attack scenes) manipulate emotional valence (positive affect vs negative affect) and modulate physiological and subjective nociceptive reactions (pleasure-induced inhibition, displeasure-induced facilitation). Using this methodology, the present study addressed 2 questions: (1) Does pain catastrophizing moderate affective reactions to standard emotional stimuli (eg, augmented negative affect)? and (2) Does pain catastrophizing moderate the relationship between emotion and nociception (eg, augmented displeasure-induced facilitation)? Erotic, neutral, and attack pictures were presented to 53 participants who rated their emotional responses. During pictures, noxious electric stimulations were delivered to evoke nociceptive reactions (nociceptive flexion reflex, skin conductance response, heart rate acceleration, subjective pain). Results suggest that pain catastrophizing did not moderate emotional reactions to standardized picture stimuli, nor did catastrophizing moderate the influence of emotion on nociceptive reactions. This suggests that catastrophizing does not influence pain indirectly through emotional processes.

PERSPECTIVE

Pain catastrophizing is commonly associated with negative emotions and maladaptive responses to pain. The current study provides evidence indicating catastrophizing does not alter pain and nociception indirectly via emotional processes.

[Definition and classification of neuropathic pain]

Neuropathic pain, following a lesion of the peripheral or primary nervous system, is characterized by a set of pathophysiologic mechanisms and a clinical expression that distinguishes it from other chronic pain, especially inflammatory pain. These two types of pain are nonetheless frequently found in the same patient. It is important to be able to recognize neuropathic pain, either isolated or associated with other chronic pain, because it requires appropriate management.

Increased pain sensitivity is not a risk factor but a consequence of frequent headache: a population-based follow-up study

Altered pain sensitivity is believed to play an important role for chronification of headache. It has however mainly been evaluated in highly selected patients from headache clinics and never in longitudinal studies. The present study is a 12-year follow-up of a population-based study of primary headache disorders and pain perception, combining a diagnostic headache interview with examination of muscle tenderness and measurement of pressure pain thresholds in 1000 subjects drawn randomly from the general population in Denmark. The aim of the study was to explore the cause-effect relationship between the increased pain sensitivity and the development of headache. The pressure pain thresholds were normal at baseline but had decreased at follow-up in subjects who developed chronic tension-type headache over the 12-year period (p = 0.025). In subjects who developed frequent episodic tension-type headache the tenderness was normal at baseline but had increased at follow-up (p < 0.01) while the pain thresholds were normal both at baseline and at follow-up. The findings demonstrate that increased pain sensitivity is a consequence of frequent tension-type headache, not a risk factor, and support that central sensitization plays an important role for the chronification of tension-type headache.

The cerebral signature for pain perception and its modulation

Our understanding of the neural correlates of pain perception in humans has increased significantly since the advent of neuroimaging. Relating neural activity changes to the varied pain experiences has led to an increased awareness of how factors (e.g., cognition, emotion, context, injury) can separately influence pain perception. Tying this body of knowledge in humans to work in animal models of pain provides an opportunity to determine common features that reliably contribute to pain perception and its modulation. One key system that underpins the ability to change pain intensity is the brainstem's descending modulatory network with its pro- and antinociceptive components. We discuss not only the latest data describing the cerebral signature of pain and its modulation in humans, but also suggest that the brainstem plays a pivotal role in gating the degree of nociceptive transmission so that the resultant pain experienced is appropriate for the particular situation of the individual.

Massaging over the greater occipital nerve reduces the intensity of migraine attacks: evidence for inhibitory trigemino-cervical convergence mechanisms

Activation of the trigemino-cervical system constitutes one of the first steps in the genesis of migraine. The objective of this study was to confirm the presence of trigemino-cervical convergence mechanisms and to establish whether such mechanisms may also be of inhibitory origin. We describe a case of a 39-years-old woman suffering from episodic migraine who showed a significant improvement in her frontal headache during migraine attacks if the greater occipital nerve territory was massaged after the appearance of static mechanical allodynia (cortical sensitization). We review trigemino-cervical convergence and diffuse nociceptive inhibitory control (DNIC) mechanisms and suggest that the convergence mechanisms are not only excitatory but also inhibitory.

Two cases of lesions in brainstem in multiple sclerosis and refractory migraine

We report on 2 cases of multiple sclerosis in patients with refractory migraine as one of the initial manifestations of the disease. In both cases, the magnetic resonance image showed lesions in the brainstem that could be implicated in the genesis of such migraine attacks.