Pain ratings and somatosensory evoked responses to repetitive intramuscular and intracutaneous stimulation in fibromyalgia syndrome.

To determine the presence of perceptual sensitization and related brain responses we examined 15 patients with fibromyalgia syndrome and 15 healthy controls comparable in age and sex. Multichannel EEG recordings and pain ratings were obtained during the presentation of 800 painful electrical intramuscular and intracutaneous stimuli to the left m. erector spinae and the left m. extensor digitorum. The stimulus intensity was adjusted to 50% between pain threshold and tolerance. Detection and pain thresholds were significantly lower in the fibromyalgia syndrome group. Sensitization occurred for both groups during intramuscular stimulation. In the EEG data the fibromyalgia syndrome patients showed higher N80 amplitudes compared with the healthy controls. Arm stimulation and intramuscular stimulation yielded higher N80 and N150 amplitudes compared with intracutaneous stimulation or stimulation of the back. These results indicate lower pain thresholds in the fibromyalgia syndrome patients after electrical stimulation and a higher N80 amplitude both indicative of enhanced sensory processing in this group.     

Psychophysiological responses to repeated acute pain stimulation in chronic low back pain patients.

Psychophysiological recordings (electrodermal activity, heart rate, respiration rate and frontalis and back muscle tension) were taken in chronic low back pain (CLBP) patients and control subjects during baseline conditions and during the presentation of six acute pressure pain stimuli. No baseline differences in back muscle tension between CLBP patients and controls were found, but CLBP patients did have higher baseline electrodermal activity. During pain stimulation, CLBP patients showed larger skin conductance reactions than controls. Also, the CLBP patient group showed a marked increase in lumbar muscle tension during the test compared to baseline, whereas the EMG level of the control group remained unchanged. This increase in muscle tension seemed to be more related to the postural change than to the pain stimulus, and it is hypothesized that some CLBP patients react with exaggerated and non-functional back muscle contractions to slight changes in posture. Contrary to expectation, no differences were found between CLBP patients and controls in physiological habituation after repeating the pain stimulus. Comparison of subjective pain ratings and psychophysiological variables showed that for control subjects arousal and subjective pain were related. For CLBP patients there was no such clear relationship.     

Differences in pain perception and sensory discrimination between chronic low back pain patients and healthy controls.

Pain perception threshold (PPT), maximal pain tolerance (MPT) and pain discrimination of CLBP patients and controls were tested. Pain perception threshold was significantly higher in the patient group for two different pain stimuli (electrical and pressure pain). Maximal pain tolerance was significantly higher in CLBP patients only for the pressure pain stimulus. There was no difference between the groups in their capacity to discriminate between painful stimuli of different intensity, as measured by a forced-choice task. It is concluded that CLBP patients have a decreased sensitivity for experimental pain. Two theories which might explain this decreased sensitivity are discussed.     

Altered cortical somatosensory processing in chronic stroke: A relationship with post-stroke shoulder pain

Post-stroke shoulder pain (PSSP), traditionally regarded as purely nociceptive pain, is often persistent and the mechanisms underlying the pain complaints are not well understood. This explorative study is the first to address the possible changes in cortical somatosensory processing in patients with PSSP. Cortical potentials were recorded following intracutaneous electrostimulaton in stroke patients with chronic PSSP (n= 6), pain-free stroke patients (PF, n=14) and healthy controls (HC, n=20) using EEG. Amplitudes and latencies of both sensory discriminative (N90) as well as cognitive evaluative (N150, P200, the N150-P200 peak-to-peak difference and P300) evoked potential components were evaluated. Stroke was associated with reduced N150 and P300 amplitudes and increased N90, N150 and P300 latencies at both sides. Compared to PF and HC, the P200 and N150-P200 latencies were increased in PSSP patients after stimulation at both sides, even when comparing subgroups with similar lesion size and location. Stroke was associated with reduced sensory-discriminative as well as with reduced cognitive-evaluative cortical somatosensory processing. This reduction was more pronounced in patients with PSSP and may be related to the central effects of persistent nociceptive pain.     

Tonic pain inhibits phasic pain: evoked cerebral potential correlates in man

In a sample of 10 healthy volunteers phasic pain ratings and evoked cerebral potentials (EPs) elicited by brief electrical skin stimuli were investigated in periods before, during, and after contralateral tonic ischemia pain. In all subjects the phasic pain ratings and the late EP components P80-N150 and N150-P260 were depressed under concurrent tonic pain. The magnitude of the mean reduction (31%, 40%, and 26%) is comparable to morphine analgesia. The early EP components with latencies below 80 ms, which are considered to be correlates of mechanosensitivity, were not influenced. The findings of tonic pain inhibiting phasic pain are discussed on the basis of changes in attention as well as of pain-specific physiological mechanisms like diffuse noxious inhibitory control.     

Chronic low back pain patient and spouse

Marital adjustment, psychological distress, health attitudes and prevalence of musculoskeletal pain symptoms were studied and compared between 63 chronic low back pain (CLBP) patients and their spouses. The CLBP patients experienced somatization significantly more than their spouses, while other psychological distress scores did not reveal statistically significant differences between the couples. The CLBP patients experienced significantly more feelings of guilt at having pain than their spouses. The patients experienced significantly more internal control, while their spouses experienced more external locus control of health. The female spouses had had significantly more musculoskeletal pain symptoms in neck and shoulders during the past week than the male spouses. The prevalence of musculoskeletal pain symptoms in the CLBP patients did not differ significantly between sexes. The results of this study are compared to population studies where the same methods have been used.     

Changes in the recruitment curve of the soleus H-reflex associated with chronic low back pain.

OBJECTIVE: We investigated whether patients with chronic low back pain (CLBP) manifest changes in the excitability of the soleus H-reflex. METHODS: H-reflex stimulus-response curve was studied in 14 CLBP patients and 14 age-matched healthy subjects. H-threshold, H-maximum size, H-steepness and H-latency were determined for both legs. Homosynaptic depression (HD), following a train of H-reflexes, and presynaptic inhibition (PI) from flexor afferents onto soleus Ia afferents were also evaluated. RESULTS: H-threshold was significantly increased, H-size as a function of stimulus intensity was significantly different, and H-recruitment curve steepness was significantly lower in CLBP patients compared to healthy subjects. No significant difference in the amount of HD and PI of the H-reflex was found between the two groups. H-latency and Hmax/Mmax ratio was comparable between the subjects groups. CONCLUSIONS: In CLBP there is a reduced excitability of group Ia afferent fibres from the soleus muscle to which presynaptic factors do not seem to contribute and that presumably depend on changes in the peripheral sensory input. SIGNIFICANCE: Changes in H-reflex excitability may underlie a decrease in the gain of a peripheral sensor in CLBP. Estimation of soleus H-threshold and H-recruitment curve may contribute to the diagnostic evaluation of CLBP and may be used to monitor the efficacy of treatment.     

Nociceptive pathway function is normal in cervical dystonia: a study using laser-evoked potentials

Cervical dystonia (CD) is often associated with pain in the neck muscles, though the mechanisms underlying pain in this condition are still largely unknown. The aim of this study was to assess laser pain rating and CO(2) laser-evoked potentials (LEPs) in CD patients with pain in the posterior neck region. We assessed the N2/P2 LEP complex and laser pain rating in a group of 20 CD patients and in 21 normal subjects. In 11 of the 20 CD patients (group I), the N2/P2 complex was recorded after stimulation of the skin overlying the right and left deltoid muscles (painless and non-dystonic). In the remaining nine CD patients (group II), the N2/P2 complex was recorded after stimulation of the skin over the splenius capitis muscle (painful and dystonic) and after stimulation of the skin overlying the contralateral splenius muscle (painless and non-dystonic). In group I patients, the N2/P2 LEP amplitude and laser pain rating after stimulation of both shoulders did not differ significantly from those obtained in normal subjects. Similarly, in group II patients, the N2/P2 LEP amplitude and laser pain rating after stimulation of the painful and dystonic splenius capitis muscle did not differ significantly from those obtained from either the contralateral painless, non-dystonic splenius capitis or normal subjects. The results of this study demonstrate that cutaneous nociceptive pathway function in CD patients is normal, thereby indicating that muscle pain in CD is not associated with any central sensitization of nociceptive inputs in either painful (dystonic) or non-painful (non-dystonic) body areas.     

The influence of transient spatial attention on the processing of intracutaneous electrical stimuli examined with ERPs

ObjectiveDetermine the influence of transient spatial attention on the processing of intracutaneous electrical stimuli.MethodsElectrical stimuli, a single pulse or five pulses, were presented at the index fingers of the left or right hand. The to-be-attended hand and stimulated finger varied randomly from trial to trial. Participants had to press a foot pedal only when the relevant stimulus, varied between participants, occurred at the attended hand. EEG was measured to extract relevant ERP components.ResultsThe N100 and N150 were enhanced for attended as compared to unattended stimuli. The N100, N150, P260, and the P500 were enlarged for five pulse as compared to single pulse stimuli. The P260, which is thought to reflect a call for attention, was enhanced for unattended as compared to attended stimuli. Source analyses indicate that attentional effects on the N100, N150, and P260 may be related to changes in activity in secondary somatosensory areas and the anterior cingulate cortex.ConclusionsA transient manipulation of spatial attention increases cortical activity induced by attended relative to unattended intracutaneous electrical stimuli, but initially unattended stimuli appear to induce an enhanced orienting effect.SignificanceInitially unattended intracutaneous electrical stimuli seem to induce a call for attention.     

Empathy for pain influences perceptual and motor processing: Evidence from response force,ERPs, and EEG oscillations

In the present study we investigated the nature and chronometry of empathy for pain influences on perceptual and motor processes. Thus, event-related brain potentials (ERPs), response force (RF) and oscillatory electroencephalography (EEG) activity were measured while participants were presented with pictures of body parts in painful or neutral situations. Their task consisted in either judging the painfulness of the stimuli or counting the body parts displayed. ERP results supported the assumption of an early automatic component of empathy for pain, as reflected by the early posterior negativity (EPN), and of a late controlled component, as reflected by the late posterior positivity (P3). RF indicated that empathy-evoking stimuli facilitate motor responses if attention is directed toward the pain dimension, whereas EEG oscillations in the mu-and beta-band revealed, independent of the task, an enhanced activation of the sensorimotor cortex after the response to painful compared to neutral stimuli. In conclusion, present findings indicate that empathy-evoking stimuli produce automatic and controlled effects on both perceptual and motor processing.     

Targeting Chronic Recurrent Low Back Pain From the Top-down and the Bottom-up: A Combined Transcranial Direct Current Stimulation and Peripheral Electrical Stimulation Intervention

BackgroundMechanisms such as neural sensitization and maladaptive cortical organization provide novel targets for therapy in chronic recurrent low back pain (CLBP).ObjectiveWe investigated the effect of a transcranial direct current stimulation (tDCS) and peripheral electrical stimulation (PES) treatment on pain, cortical organization, sensitization and sensory function in CLBP.MethodsUsing a placebo-controlled crossover design, 16 individuals received four treatments in separate sessions: i) anodal tDCS/PES; ii) anodal tDCS/sham PES; iii) sham tDCS/PES; or iv) sham tDCS/sham PES. Pain was assessed at baseline, immediately following, and at 1 and 3 days after treatment. Motor cortical organization, sensitization and sensory function were measured before and immediately after treatment.ResultsCombined tDCS/PES reduced pain and sensitization, normalized motor cortical organization and improved sensory function. The reduction in pain was greater in individuals with more pronounced sensitization. Applied alone, tDCS or PES also reduced pain. However, with the exception of improved sensory function and reduced map volume following PES, clinical and neurophysiological outcomes were unaltered by tDCS or PES applied separately. No changes were observed following sham treatment.ConclusionOur data suggest a combined tDCS/PES intervention more effectively improves CLBP symptoms and mechanisms of cortical organization and sensitization, than either intervention applied alone or a sham control.     

Performance level of chronic low back pain patients in different treadmill test conditions

An experimental group of 39 chronic low back pain (CLBP) patients and an equal number of control subjects matched for age and sex were tested with a standardized back stress physical test. The subjects were given no indication of the performance expected and no feedback was given during the test. The test was repeated with a high frame of reference and feedback offered to the subjects. In the latter condition the control group improved their performance in contrast to the CLBP group. The poorer performance of the CLBP patients in both conditions was unrelated to pain increase, post-test pain level or poor physical condition. However, there is a clear relationship between performance and pre-test pain level, especially in the feedback condition. In this condition, it also seems that increasing pain level during the test is used as a ‘rationalization’ for the built-in failure experience. Compared to the control group the CLBP patients were less able to estimate their physiological level of exertion and were inclined to overrate their actual effort.     

Cognitive effects of precentral cortical stimulation for pain control: an ERP study.

Electrical stimulation of the motor cortex (MCS) is a promising and increasingly used neurosurgical technique for the control of refractory neuropathic pain. Although its mechanisms of action remain unknown, recent functional imaging data suggest involvement of the thalamus, brainstem and anterior cingulate/orbitofrontal cortex. Since some of these areas are also implicated in higher cognitive functions, notably attentional processes, we analysed cognitive ERPs and behavioural performance during an "oddball" auditory detection task in patients submitted to this procedure. Eleven consecutive patients undergoing MCS because of neuropathic refractory pain, ranging in age from 25 to 71 years, were included in the study. ERPs were obtained in all cases both during the application ("MCS-on") and within the 10 min that followed discontinuation of the procedure ("MCS-off"). In five patients, ERPs could also be obtained just before the start of MCS. When the patients' sample was taken as a whole, there were no consistent effects of MCS on the ERPs. There was, however, a significant interaction of MCS action with the patients' age, reflecting a significant delay during MCS of the cognitive responses N2 and P3 (N200 and P300) in the group of patients older than 50 years exclusively. This effect was rapidly reversible after MCS discontinuation. No MCS-related changes were observed in the N1 component. At the individual level, the effect of MCS on the endogenous ERPs was highly variable, ranging from a total stability of ERPs (mostly in younger subjects) to latency differences of tens of milliseconds in the older group. These results, together with recent experiments showing P300 alteration during repetitive transcranial stimulation, suggest that motor cortex stimulation may interfere with relatively simple cognitive processes such as those underlying target detection, and that the risk of abnormal cognitive effects related to cortical stimulation may increase with age. Although the procedure appears on the whole remarkably safe, complementary neuropsychological studies in this category of patients are advised, as well as caution to possible adverse cognitive effects when using MCS in the elderly, notably in the presence of pre-existent cerebral lesions.     

Cortical thickness and functional connectivity abnormality in chronic headache and low back pain patients

This study aims to characterize the psychological wellbeing of chronic headache (CH) patients, to identify cortical structural abnormalities and any associations of those abnormalities with resting state functional connectivity (rsFC), and to determine whether such rsFC abnormality is specific to CH patients. Compared with healthy controls (CON_CH), CH patients suffered from mild depression, sleep disturbances, and relatively poor quality of life. CH patients also exhibited widespread cortical thickness (CT) abnormalities in left premotor (BA6), right primary somatosensory (S1) and right prefrontal (BA10) cortices, as well as in regions of default mode and executive control networks. Using cortical regions with thickness abnormality as seeds, we found cortical region pairs showed strengthened rsFC in CH patients. Using the same seeds, rsFC analysis from chronic low back pain (CLBP) patients and their controls (CON_CLBP) identified abnormalities in non‐overlapping cortical region pairs. Direct comparison of rsFC between CH and CLBP patients revealed significantly differences in thirteen cortical region pairs, including the four identified in CH and CON_CH comparison. Across all three groups (CH, CLBP and CON), the rsFC between left multisensory association area (BA39) and left posterior cingulate cortex (BA23) differed significantly. Eight regions showed CT abnormality in CLBP patients, two of which overlapped with those of CH patients. Our observations support the notion that CH and CLBP pain are pathological conditions, under which the brain develops distinct widespread structural and functional abnormalities. CH and CLBP groups share some similar structural abnormalities, but rsFC abnormalities in several cortical region pairs appear to be pathology‐specific. Hum Brain Mapp 38:1815–1832, 2017. © 2017 Wiley Periodicals, Inc.     

A controlled study of couple therapy in chronic low back pain patients. Effects on marital satisfaction, psychological distress and health attitudes.

This was a controlled, prospective study on the effectiveness of couple therapy in 63 chronic low back pain patients (CLBP) from primary health care centers. They were randomly allocated to a couple therapy (T) group, N = 33, and to a control (C) group, N = 30. Couple therapy consisting of five monthly sessions was conducted by two family therapists. All patients and their spouses participated in a 12-month follow-up. Marital communication improved in CLBP patients of the T-group, whereas it worsened in the C-group. Psychological distress decreased in male patients of the T-group, whereas it increased in male patients of the C-group. However, due to high initial levels of distress in male patients of the T-group no firm conclusion of therapy effect can be done. The trends in health attitudes of the patients were similar during the study year. No significant differences in any of the measures were found in spouses. It is concluded that couple therapy improves the quality of life in CLBP patients by enhancing marital communication.     

Effects of myofascial-meridian stimulation therapy (mmst) on shoulder pain

Fifty patients with shoulder pain were classified into two groups according to the type of pain: a capsular-pattern group (N = 22) and a non-capsular-pattern group (N = 28). Both groups received myofascial-meridian stimulation therapy four times in two weeks. After therapy, the pain level was significantly lower in the capsular-pattern than in the non-capsular-pattern group. The capsular-pattern group showed a nonsignificant trend toward greater range of motion than the non-capsular-pattern group. These data suggest that myofascial-meridian stimulation therapy might be useful as a new treatment to reduce pain and increase range of motion in patients with shoulder pain.     

Cognitive factors in the performance level of chronic low back pain patients

An experimental group of 39 chronic low back pain (CLBP) patients and an equal number of controls, matched for age and sex, completed questionnaires of self-concept and performance motivation. SS were also tested on a standardized back-stress physical test carried out with low external information and feedback. The results revealed a strong tendency for CLBP patients to have a negative self-concept, confirming the findings of previous research. Poorer performance of the CLBP patients on the physical test measure of behavioural persistence and on physiological measures were unrelated to reported pain level or to poor physical condition. Compared to the controls, the chronic low back pain group was less able to estimate their physiological level of exertion, being inclined to overrate their actual individual effort. The interaction of a negative self-concept and negative expectations is discussed.     

Sensitization and pain

Migraine is often accompanied with signs of increased intracranial and extracranial mechanical sensitivities. The prevailing view today is that migraine headache is a neurovascular disorder with intracranial origin and involvement of meningeal blood vessels and their pain nerve fibers. Allodynia, defined as perception of pain following not painful stimulation, is a common clinical feature in various pain syndromes, and as part of migraine pain, it can be considered an indicator of trigeminal neural network sensitization. The cutaneous allodynia that accompanies the migraine headache in a large percentage of patients may be considered the clinical expression of central nervous system sensitization and is characterized by pain provoked by stimulation of the skin that would ordinarily not produce pain. An altered codification process of sensory impulses in the brainstem, in particular by the nucleus caudalis trigeminalis, may justify the temporal aspects and symptoms in the course of migraine attack.     

Both pain and EEG response to cold pressor stimulation occurs faster in fibromyalgia patients than in control subjects

Pain-evoked brain potentials elicited by laser stimulation have been repeatedly shown to be abnormal in fibromyalgia syndrome. However, to our knowledge this is the first study assessing enduring (cold pressor) pain and correlated EEG changes in fibromyalgia. EEG power and subjective pain ratings during the cold pressor test were analyzed and contrasted with tasks not involving sensory stimulation (rest, mental arithmetic and pain imagery) in 20 patients with fibromyalgia and 21 healthy control subjects. Fibromyalgia patients both perceived pain and judged pain as intolerable earlier than control subjects, while pain intensity ratings and EEG power changes during subjective awareness of pain were similar in both groups. In patients and control subjects, pain was correlated with a rise in delta, theta and beta power. EEG power spectra during pain imagery and mental arithmetic were significantly different from those observed during the cold pressor test. In conclusion, fibromyalgia patients seem to process painful stimuli abnormally in a quantitative sense, thus producing both the sensation of pain, as well as the associated EEG patterns, much earlier than control subjects. However, the quality of the pain-associated EEG changes seems similar.