[Assessing pain in patients with dementia]. / Schmerzerfassung bei Patienten mit Demenz.

The diagnostics of pain in older people with cognitive impairments should always consist of a subjective self-report of pain and a structured observation of pain behavior. It is important to note that the subjective self-report of pain becomes less valid with increasing cognitive decline (starting with a moderate degree of dementia). The external observation of pain behavior should include at least the three behavioral domains facial expressions, body movements and vocalization and should be performed during resting situations and during activities of daily living. Moreover, the patient should be observed for at least 3 min. Online forms of training have recently been developed and are freely available for training in external observation.

Prediction of persistent post-operative pain: Pain-specific psychological variables compared with acute post-operative pain and general psychological variables.

BACKGROUND: Psychological variables and acute post-operative pain are of proven relevance for the prediction of persistent post-operative pain. We aimed at investigating whether pain-specific psychological variables like pain catastrophizing add to the predictive power of acute pain and more general psychological variables like depression. METHODS: In all, 104 young male patients undergoing thoracic surgery for pectus excavatum correction were studied on the pre-operative day (T0) and 1 week (T1) and 3 months (T2) after surgery. They provided self-report ratings (pain-related: Pain Catastrophizing Scale, Pain Anxiety Symptoms Scale = PASS, Pain Vigilance and Awareness Questionnaire = PVAQ; general psychological: Screening for Somatoform Symptoms, State-Anxiety Inventory-X1, Center for Epidemiologic Studies Depression Scale = CES-D). Additional predictors (T1) as well as criterion variables (T2) were pain intensity (Numerical Rating Scale) and pain disability (Pain Disability Index). RESULTS: Three months after surgery, 25% of the patients still reported clinically relevant pain (pain intensity ≥3) and over 50% still reported pain-related disability. Acute post-operative pain as well as general psychological variables did not allow for a significant prediction of persistent post-operative pain; in contrast, pain-related psychological variables did. The best single predictors were PASS for pain intensity and PVAQ for pain disability. CONCLUSIONS: Pain-related psychological variables derived from the fear-avoidance model contributed significantly to the prediction of persistent post-operative pain. The best possible compilation of these measures requires further research. More general psychological variables may become relevant predictors later in the medical history. SIGNIFICANCE: Our results suggest that pain-specific psychological variables such as pain anxiety and pain hypervigilance add significantly to the prediction of persistent post-operative pain and might even outperform established predictors such as acute pain and general psychological variables. Clinicians might benefit from the development of time-economic screening tools based on these variables.

Startle modulation by heat pain with varying threat levels in chronic pain patients and pain-free controls.

BACKGROUND: Empirical evidence suggests that affective responses to pain are changed in chronic pain. The investigation of startle responses to pain might contribute to clarifying whether such alterations also expand to motivational defensive reactions. We aimed at comparing startle responses to tonic heat pain with high threat (HT) or low threat (LT) in patients with chronic musculoskeletal pain and controls. As pain-related anxiety and catastrophizing are typically elevated in chronic pain, we expected to find stronger startle responses in patients specifically under experimental HT. METHODS: Patients with chronic musculoskeletal, preferentially, back pain (N = 19) and matched pain-free controls (N = 19) underwent two pain-related threat conditions (high and low) in balanced order. Only, in the HT condition, 50% of the trials were announced to include a short further noxious temperature increase at the end. Startle responses to loud tones were always assessed prior to a potential temperature increase in the phase of anticipation and were recorded by surface electromyogram. RESULTS: Surprisingly, we observed no differences in startle responses and ratings of emotional and pain responses between patients and controls despite significantly higher pain-related anxiety and catastrophizing in the patients. Overall, startle was potentiated in the HT condition, but only in participants who started with this condition. CONCLUSION: Our results suggest that, in general, patients with pain are not more responsive emotionally to experimental threat manipulations despite elevated pain anxiety and catastrophizing. Instead, exaggerated responses in patients might be triggered only by individual concerns relating to pain, which are not sufficiently mirrored by our threat paradigm.

Psychometric Properties of the German Version of the Pain Vigilance and Awareness Questionnaire (PVAQ) in Pain-Free Samples and Samples with Acute and Chronic Pain.

PURPOSE: The way individuals attend to pain is known to have a considerable impact on the experience and chronification of pain. One method to assess the habitual "attention to pain" is the Pain Vigilance and Awareness Questionnaire (PVAQ). With the present study, we aimed to test the psychometric properties of the German version of the PVAQ across pain-free samples and across patients with acute and chronic pain. METHOD: Two samples of pain-free individuals (student sample (N = 255)/non-student sample (N = 362)) and two clinical pain samples (acute pain patients (N = 105)/chronic pain patients (N = 36)) were included in this cross-sectional evaluation of the German PVAQ. Factor structure was assessed using exploratory and confirmatory factor analyses. Reliability was assessed using internal consistency (Cronbach's alpha). Construct validity was tested by assessing correlations between PVAQ and theoretically related constructs. RESULTS: Exploratory factor analysis (non-student sample) and confirmatory factor analysis (student sample, acute pain patient sample) suggested that a two-factor solution best fitted our data ("attention to pain," "attention to changes in pain"). Internal consistency ranged from acceptable to good in all four samples. As hypothesized, the PVAQ correlated significantly with theoretically related constructs in all four samples, suggesting good construct validity in pain-free individuals and in pain patients. CONCLUSION: The German PVAQ shows good psychometric properties across samples of pain-free individuals and patients suffering from pain that are comparable to PVAQ versions of other languages. Thus, the German PVAQ seems to be a measure of pain vigilance equally valid as found in other countries.

Improving recognition of pain by calling attention to its various faces.

BACKGROUND: The ability to accurately recognize facial expressions of pain is known to affect clinical decision making and delivery of care. Although recognition accuracy for facial expressions of pain is well above chance level, substantial shortcomings have also been reported which stress the need to look for methods to improve recognition accuracy. Based on findings that pain is encoded in different facial activity patterns, we wanted to investigate whether training observers to recognize these various faces of pain might improve their ability to accurately recognize pain. METHODS: Participants (55 male, 65 female) were randomly assigned to one of the three training groups: 'different patterns group' (calling attention to the various faces of pain); 'prototypical group' (calling attention to the prototypical expression of pain); and 'control group' (being informed about pain in general). For outcome assessments, participants viewed videos of individuals experiencing either pain, disgust or a neutral condition and had to infer what the individual in the video was experiencing. These videos were presented twice (before and after the training). RESULTS: The 'different patterns group' benefited the most from its training, with recognition accuracy for pain increasing significantly more compared to the other groups. The 'prototypical' group also showed improved recognition accuracy for pain, however, this improved recogntition was cancelled out by decreased recognition accuracy for disgust. CONCLUSIONS: Raising awareness in observers that different combinations of facial movements (different faces of pain) are equivalent signals of pain through a brief training procedure can improve recognition accuracy for pain substantially.

No effects of hydrocortisone and dexamethasone on pain sensitivity in healthy individuals.

BACKGROUND: There is some evidence that stress-induced cortisol increase leads to a decrease in pain, while lowering cortisol levels enhances pain sensitivity, but no study has yet investigated both pharmacological enhancement and reduction of cortisol levels in the same individuals. METHODS: Firstly, we tested in 16 healthy individuals whether the treatment with hydrocortisone and dexamethasone, respectively, results in altered pain thresholds. Secondly, we aimed to test whether hormone effects are different across the pain range by using ratings for pain stimuli with varying intensity; and thirdly, we tested whether cortisol levels influence the discrimination ability for painful stimuli. RESULTS: Despite substantial effects of dexamethasone and hydrocortisone administration on cortisol levels, no effect of these drugs was seen in terms of pain sensitivity (pain threshold, pain rating, pain discrimination ability), although comprehensively examined. However, in the placebo condition, a significant negative correlation between cortisol and pain thresholds was seen. Similarly, there were also strong negative associations between cortisol levels in the placebo condition and pain thresholds after drug treatment (especially after hydrocortisone). CONCLUSION: These findings suggest that short-term variations of cortisol do not influence pain sensitivity whereas, in general, high levels of cortisol are associated with increased pain sensitivity, at least for weak to moderate stimuli.

Gaze behaviour when monitoring pain faces: An eye-tracking study.

BACKGROUND: The vigilance-(attentional) avoidance hypothesis (VAH) developed for explaining phobic reactions describes an early attentional bias towards a feared stimulus followed by attentional avoidance of this stimulus. Such a pattern of attentional shifts might also be found when processing of pain-related stimuli is required. The purpose of the present study was to test the VAH for pain-associated stimuli, i.e., faces displaying pain, using the method of eye-tracking in a pain-free sample. METHODS: Forty-eight healthy participants observed pictures of faces displaying pain and other emotions (anger, joy), presented concurrently with neutral faces, while their gaze behaviours were recorded continuously. RESULTS: Analysis of the time course of fixation durations revealed a distinct pattern for pain faces. Participants gazed at pain faces longer than at neutral faces at the beginning (up to 1000 ms) but reduced preference for pain faces increasingly thereafter (up to 2000 ms); this decline in vigilance did not occur for anger and joy faces. Strong fear of pain (Fear of Pain Questionnaire) tended to increase attentional preference for negative faces (pain, anger), a finding, which however did not reach significance. CONCLUSIONS: We assume that initial vigilance for pain-associated stimuli might reflect an adaptive reaction to detect a potentially harmful stimulus. Subsequently, the pain-associated stimulus might be less attended for the purpose of mood regulation when all clear is given in this situation.

Modulation of the startle reflex by heat pain: does threat play a role?

BACKGROUND: Previous studies have indicated that the startle reflex is potentiated by phasic, but not by tonic, heat pain, although the latter is seen as more strongly associated with emotional responses and more similar to clinical pain. The threat value of pain might be a decisive variable, which is not influenced alone by stimulus duration. OBJECTIVE: This study aimed at comparing startle responses to tonic heat pain stimulation with varying degrees of threat. We hypothesized that the expectation of unpredictable temperature increases would evoke higher threat and thereby potentiate startle compared with the expectation of constant stimulation. METHODS: Healthy, pain-free subjects (n = 40) underwent painful stimulation in two conditions (low/high threat) in balanced order. The only difference between the two conditions was that in the high-threat condition 50% of the trials were announced to include a short further noxious temperature increase at the end. Startle tones were presented prior to this temperature increase still in the phase of anticipation. RESULTS: We observed startle potentiation in the high-threat compared with the low-threat condition, but only in those participants who took part first in the high-threat condition. Habituation could not account for these findings, as we detected no significant decline of startle responses in the course of both conditions. CONCLUSIONS: Our results suggest that subjective threat might indeed be decisive for the action of pain on startle; the threat level appears not only influenced by actual expectations but also by previous experiences with pain as threatening or not.

[Psychological prophylaxis training for coping with postoperative pain. Long-term effects]. / Psychologisches Prophylaxetraining zur Bewältigung postoperativer Schmerzen. Langfristige Effekte.

INTRODUCTION: The present study was performed to investigate the effect of multidimensional psychological prophylaxis training focusing on coping with cognitive-emotional pain on recovery within the first 12 months after surgery. The training included the following three components: (1) education about pain, analgesia and psychological aspects of coping with pain, (2) training for coping with pain and (3) body-centered relaxation. MATERIAL AND METHODS: In the study 48 young male patients (surgical correction of a chest malformation) were assessed 1 day before surgery, at discharge and 3, 6 and 12 months postoperatively concerning postoperative pain intensity and pain disability as well as pain anxiety, pain catastrophizing and pain hypervigilance. Additionally, 24 of these patients received training on cognitive-emotional coping with pain 1 day before surgery and 1-3 days after surgery (each session 1 h). RESULTS: The proportion of patients with clinically relevant improvement was significantly higher in the training group compared to the control group. This was the case for acute pain intensity (approximately 1 week after surgery), pain disability 3 months later and pain anxiety 12 months after surgery. CONCLUSION: The resurgence of pain anxiety after 12 months could only be found in the control group and could be due to the upcoming surgical removal of the transsternal metal implant. The prophylaxis training can therefore be seen as a protective factor for long-term management of surgery-related consequences and future pain experiences.

[Sleep deprivation and pain: a review of the newest literature]. / Schlafentzug und Schmerz : Ein Review der neuesten Literatur.

It has now been established that sleep deprivation or fragmentation causes hyperalgesia which cannot be explained by a general change in somatosensory perception. However, it has not yet been clarified which of the sleep stages are most relevant for this effect. The seemingly paradoxical effects of sleep deprivation on pain-evoked brain potentials on the one hand and the subjective pain report on the other hand suggest complex changes in gating mechanisms. As the effects on pain and affect can be dissociated a common mechanism of action seems unlikely. Data from animal studies suggest that hyperalgesia due to sleep deprivation might be particularly strong under preexisting neuropathic conditions. Together with results from animal research the finding that endogenous pain modulation (CPM) is impaired by sleep deprivation suggests that the serotoninergic system mediates the effect of sleep deprivation on pain perception. However, other neurotransmitters and neuromodulators still have to be considered. The clinically relevant question arises why sleep deprivation induces hyperalgesia more easily in certain individuals than in others and why this effect then has a longer duration?

Endogenous pain inhibition during menstrual cycle in migraine.

BACKGROUND: Migraine is a common headache disorder that can vary menstrually in women and has been linked to an impairment of endogenous pain inhibitory systems. One of these endogenous pain inhibitory systems, namely conditioned pain modulation (CPM; formerly diffuse noxious inhibitory controls-like), has been shown to be affected by the menstrual cycle. The aim of this study was to examine CPM over the menstrual cycle in migraineurs and healthy controls. METHODS: Twenty healthy women and 32 female migraineurs were examined on days 1, 4, 14 and 22 of the menstrual cycle. Detection and pain thresholds for electrocutaneous stimuli were first assessed at baseline. Second, tonic heat stimuli were applied concurrently to the electrical stimuli, and the difference in electrical thresholds to baseline were analysed as indicating CPM inhibition. RESULTS: Migraineurs revealed higher detection thresholds than the control group but similar pain thresholds for the electrical current. Likewise, pain sensitivity for tonic heat stimulation also did not differ between groups. With regard to our main hypotheses, we found that CPM inhibition neither differed between migraineurs and healthy volunteers nor varied over the menstrual cycle. CONCLUSIONS: Our findings suggest that CPM inhibition is not altered in female migraineurs; thus, it is questionable whether CPM really plays a role in the development of migraine or whether migraine leads to a dysfunctional CPM inhibition.

The faces of pain: a cluster analysis of individual differences in facial activity patterns of pain.

BACKGROUND: There is general agreement that facial activity during pain conveys pain-specific information but is nevertheless characterized by substantial inter-individual differences. With the present study we aim to investigate whether these differences represent idiosyncratic variations or whether they can be clustered into distinct facial activity patterns. METHODS: Facial actions during heat pain were assessed in two samples of pain-free individuals (n = 128; n = 112) and were later analysed using the Facial Action Coding System. Hierarchical cluster analyses were used to look for combinations of single facial actions in episodes of pain. The stability/replicability of facial activity patterns was determined across samples as well as across different basic social situations. RESULTS: Cluster analyses revealed four distinct activity patterns during pain, which stably occurred across samples and situations: (I) narrowed eyes with furrowed brows and wrinkled nose; (II) opened mouth with narrowed eyes; (III) raised eyebrows; and (IV) furrowed brows with narrowed eyes. In addition, a considerable number of participants were facially completely unresponsive during pain induction (stoic cluster). These activity patterns seem to be reaction stereotypies in the majority of individuals (in nearly two-thirds), whereas a minority displayed varying clusters across situations. CONCLUSION: These findings suggest that there is no uniform set of facial actions but instead there are at least four different facial activity patterns occurring during pain that are composed of different configurations of facial actions. Raising awareness about these different 'faces of pain' might hold the potential of improving the detection and, thereby, the communication of pain.

[Central pain processing and Parkinson's disease. Epidemiology, physiology, and experimental results issuing pain processing]. / Zentrale Schmerzverarbeitung bei Morbus Parkinson. Epidemiologie, Physiologie und experimentelle Befunde zur Schmerzverarbeitung.

Parkinson's disease (PD) is caused by degeneration of the dopaminergic neurons in the substantia nigra (SN) and a resulting dysfunction of the nigrostriatal pathways including the basal ganglia. Beside motor symptoms, different types of pain (e.g., dystonic musculoskeletal pain or central pain) occur in a considerable number of patients. In addition, abnormalities in pain processing have been observed in PD patients, which may present as increased pain sensitivity. The pathophysiological mechanisms involved in disturbed pain processing of PD, however, are still poorly understood. The present article gives an overview of the relevant experimental studies, investigating the abnormalities of pain processing in PD by means of electrophysiological [electroencephalography (EEG), sympathetic skin response (SSR)] and psychophysical methods [quantitative sensory testing (QST), RIII reflex threshold]. Based on a review of the literature, it is postulated that dysfunction in endogenous pain inhibition caused by dopaminergic deficiency in the basal ganglia, especially in the striatum, but also in mesolimbic areas is a main pathophysiological mechanism involved in nociceptive abnormalities in PD.

Menstrual variation in experimental pain: correlation with gonadal hormones.

BACKGROUND: The results of studies examining the response to experimental pain during the menstrual cycle are conflicting because of differences in the definitions of the menstrual period, outcome measures and types of experimental pain stimulation. So far, there have been only a few studies correlating experimental pain with the levels of gonadal hormones over the menstrual cycle. Therefore, we assessed the responses to multiple experimental pain stimuli during the menstrual cycle and computed their correlations with the salivary concentrations of the gonadal hormones estrogen and testosterone. METHODS: Twenty-four healthy and regularly menstruating women between 20 and 41 years old took part in the study. Detection thresholds (warmth, cold and electrical current) and pain thresholds (cold, heat, pressure and electrical current) were assessed on days 1, 4, 14 and 22 of the menstrual cycle. In each session, salivary samples were collected for the determination of the physiological estrogen 17beta-estradiol, progesterone and testosterone. Progesterone was used exclusively to verify regular menstrual cycling. RESULTS: Significant variations in pain thresholds for cold, pressure and electrical stimuli were observed over the menstrual cycle with the highest thresholds on day 22, except for the cold pain thresholds, which peaked on day 14. There were no such changes regarding heat pain and all the detection thresholds. The correlations separately computed for each of the 4 days between salivary estrogen as well as testosterone on the one hand and the detection or pain thresholds on the other hand failed to show significant levels, except for the coupling of testosterone and electrical pain thresholds on day 1. CONCLUSIONS: The pain thresholds for all the physical stressors increased after menstruation. The acrophases were located in the follicular (cold pain threshold) or in the luteal phase (pressure and electrical pain thresholds). The results of our correlation analyses indicate only minimal influences of the physiological levels of gonadal hormones on pain sensitivity in women.

Pain sensitivity and descending inhibition of pain in Parkinson's disease.

BACKGROUND: Patients suffering from Parkinson's disease (PD) often complain about painful sensations. Recent studies detected increased subjective pain sensitivity and increased spinal nociception, which appeared to be reversible by dopaminergic treatment. Possibly, reduced descending pain inhibition contributes to this finding. OBJECTIVE: Subjective pain thresholds as well as nociceptive reflex thresholds were investigated to isolate potential loci of the pathophysiological changes within the pain pathway. In addition, the diffuse noxious inhibitory control (DNIC) system as one form of descending control was assessed. METHOD: 15 patients with PD and 18 controls participated in the study. Electrical and heat pain thresholds as well as the nociceptive flexion reflex (NFR) thresholds were determined. Thereafter, the electrical pain thresholds were measured once during painful heat stimulation (conditioning stimulation) and twice during innocuous stimulation (control stimulation). RESULTS: Patients with PD exhibited lower electrical and heat pain thresholds as well as lower NFR thresholds. Suppression of the electrical pain thresholds during painful heat stimulation (conditioning stimulation) compared with control stimulation did not differ significantly between the groups. No differences in the thresholds between patients with PD with and without clinical pain were seen. CONCLUSIONS: Finding the NFR threshold to be decreased in addition to the decreased electrical and heat pain thresholds indicates that the pathophysiological changes either already reside at or reach down to the spinal level. Reduced activation of the DNIC system was apparently not associated with increased pain sensitivity, suggesting that DNIC-like mechanisms do not significantly contribute to clinical pain in PD.

[Multidimensional pain assessment in patients with dementia]. / Mehrdimensionale Schmerzmessung bei Demenzpatienten.

BACKGROUND: It is well known that patients with dementia complain less about pain and receive fewer analgesics than other patients. The question arises of whether disorders associated with dementia change the processing of pain. METHODS: A total of 20 patients with dementia and 40 patients with mild cognitive impairment (MCI) as well as 40 healthy control subjects were investigated for their subjective (category scale), facial (FACS) and motor (R-III reflex) pain responses to mechanical and electrical stimuli. RESULTS: Patients with dementia did not rate the intensity of the stimuli differently; however, they were less frequently capable of providing ratings. At equal levels of stimulus intensity, demented patients showed stronger facial responses. The R-III reflex thresholds were lowered in demented patients. MCI patients appeared only slightly changed. CONCLUSIONS: Our findings suggest that the processing of acute noxious stimuli is intensified in patients with dementia. Against the background of a reduced prescription of analgesics, an under-treatment of pain in patients with dementia might be the consequence.

EEG responses to tonic heat pain.

The aim of the present study was to characterize the EEG response pattern specific for tonic pain which is an experimental pain model resembling clinical pain more closely than phasic pain. Tonic experimental pain was produced by a series of heat pulses 1 degree C above pain threshold over 10 min. A series of heat pulses 0.3 degree C below pain threshold and a constant temperature of 37 degrees C served as non-painful heat control and as baseline condition, respectively. The level of attention was experimentally manipulated by instruction and by a distraction task. Twenty male, pain-free subjects had to rate the sensation intensity and sensation unpleasantness during thermal stimulation. Furthermore, a German version of the McGill Pain Questionnaire was to be filled out after tonic painful heat stimulation. The EEG was recorded via 10 leads according to 10/20 convention. Power density was calculated for the usual frequency bands. The ratings showed that tonic painful heat was experienced clearly distinct from tonic non-painful heat. An EEG response pattern emerged characterized by a rather generalized increased delta(2) activity, a left-biased fronto-temporally diminished theta activity, a fronto-temporal decrease in the alpha(1) activity and a left-sided temporal increase in the beta(1) activity. This observation agrees well with the findings of others. However, there was no evidence in our data that these EEG changes are specific to tonic heat pain as opposed to changes observed during tonic non-painful heat stimulation. Accordingly, the repeatedly reported EEG patterns are also likely to be produced by other forms of strong somatosensory stimuli and to be not specific for pain.

[The impact of Alzheimer's disease on the pain processing]. / Einfluss der Alzheimer-Erkrankung auf die Schmerzverarbeitung.

It is well known that patients with Alzheimer's disease report less pain in comparison to their age group. However, little is yet known about the underlying mechanisms causing the decreased pain report. In order to learn more about these mechanisms, experimental studies are indispensable, since only in experimental settings, noxious input and pain experience can be assessed independently. We therefore report on experimental data on pain perception in Alzheimer's disease in this review. The experimental data suggest that the threshold for pain tolerance is markedly increased and the autonomic pain reaction is, at least in part, considerably diminished. On the other hand, pain threshold and pain event-related brain potentials remain largely unchanged. As possible explanations we discuss age-related changes in pain perception and neuroanatomical changes in Alzheimer's disease. Particularly the atrophy of limbic structures may have a modifying impact on the pain experience. We also discuss what influence communicational deficits have on pain report.

Spatial summation of heat pain in males and females.

Sex differences in pain sensitivity have been found to vary between considerable and negligible. It has appeared that the pain stimulation method is critical in this context. It was assumed this might be due to the different degrees of spatial summation associated with the different pain stimulus modalities. Hence, sex differences were investigated in spatial summation of heat pain in 20 healthy women and 20 healthy men of similar age. Pain thresholds were assessed by a tracking procedure and responses to supra-threshold pain stimulation by numerical ratings. Heat stimuli were administered by a thermode with contact areas of 1, 3, 6 and 10 cm2. Pain thresholds were significantly higher with smaller areas stimulated than with larger ones. No significant effect of area was found for the ratings of the supra-threshold stimuli, the intensities of which were tailored to the individual pain threshold. Consequently, spatial summation of heat pain appeared to result mainly in a shift of the pain threshold on the ordinate and not a change of slope of the stimulus-response function in the pain range. In neither of the two pain parameters were there any sex differences. Therefore, the present study demonstrated that sex differences in spatial summation of heat pain are unlikely.

Sex differences in musculoskeletal pain.

Epidemiologic, clinical, and experimental evidence points to sex differences in musculoskeletal pain. Adult women more often have musculoskeletal problems than do men. Discrepant findings regarding the presence of such differences during childhood and adolescence continue. Biologic and psychosocial factors might account for these differences. The authors review evidence showing that mechanically induced pressure is more likely to show sex differences than other noxious stimuli and to discriminate between individuals suffering from musculoskeletal pain and matched controls. The authors suggest that a state of increased pain sensitivity, with a peripheral or central origin, predisposes individuals to chronic muscle pain conditions, and that there are sex differences in the operation of these mechanisms; women are vulnerable to the development and maintenance of musculoskeletal pain conditions.