Neural activation during acute capsaicin-evoked pain and allodynia assessed with PET

The PET H2 15O-bolus method was used to image regional brain activity in normal human subjects during intense pain induced by intradermal injection of capsaicin and during post-capsaicin mechanical allodynia (the perception of pain from a normally non-painful stimulus). Images of regional cerebral blood flow were acquired during six conditions: (i) rest; (ii) light brushing of the forearm; (iii) forearm intradermal injection of capsaicin, (iv) and (v) the waning phases of capsaicin pain; and (vi) allodynia. Allodynia was produced by light brushing adjacent to the capsaicin injection site after ongoing pain from the capsaicin injection had completely subsided. Capsaicin treatment produced activation in many discrete brain regions which we classified as subserving four main functions: sensation-perception (primary somatosensory cortex, thalamus and insula); attention (anterior cingulate cortex); descending pain control (periaqueductal grey); and an extensive network related to sensory-motor integration (supplementary motor cortex, bilateral putamen and insula, anterior lobe and vermis of the cerebellum and superior colliculus). Comparison of the noxious and non-noxious stimuli yielded several new insights into neural organization of pain and tactile sensations. Capsaicin pain, which had no concomitant tactile component, produced little or no activation in secondary somatosensory cortex (SII), whereas light brushing produced a prominent activation of SII, suggesting a differential sensitivity of SII to tactile versus painful stimuli. The cerebellar vermis was strongly activated by capsaicin, whereas light brush and experimental allodynia produced little or no activation, suggesting a selective association with C-fibre stimulation and nociceptive second-order spinal neurons. The experimental allodynia activated a network that partially overlapped those activated by both pain and light brush alone. Unlike capsaicin-induced pain, allodynia was characterized by bilateral activation of inferior prefrontal cortex, suggesting that prefrontal responses to pain are context dependent.

Unilateral decrease in thalamic activity observed with positron emission tomography in patients with chronic neuropathic pain

The oxygen-15 water bolus positron emission tomography (PET) method was used to image regional brain activity in 4 patients with chronic post-traumatic neuropathic pain confined to one lower limb and in 1 patient with post-herpetic neuralgia. In comparison to 13 normal subjects, scans of the patients disclosed a statistically significant decrease in thalamic activity contralateral to the symptomatic side. Examination of the right/left ratio for all the subjects showed that the values for the patients fell at the extremes of the normal range, according to the side of the affected body part. These initial observations suggest that functional alterations in thalamic pain processing circuits may be an important component of chronic neuropathic pain.

Experimental cranial pain elicited by capsaicin: a PET study

Using a positron emission tomography (PET) study it was shown recently that in migraine without aura certain areas in the brain stem were activated during the headache state, but not in the headache free interval. It was suggested that this brain stem activation is inherent to the migraine attack itself and represents the so called 'migraine generator'. To test this hypothesis we performed an experimental pain study in seven healthy volunteers, using the same positioning in the PET scanner as in the migraine patients. A small amount of capsaicin was administered subcutaneously in the right forehead to evoke a burning painful sensation in the first division of the trigeminal nerve. Increases of regional cerebral blood flow (rCBF) were found bilaterally in the insula, in the anterior cingulate cortex, the cavernous sinus and the cerebellum. Using the same stereotactic space limits as in the above mentioned migraine study no brain stem activation was found in the acute pain state compared to the pain free state. The increase of activation in the region of the cavernous sinus however, suggests that this structure is more likely to be involved in trigeminal transmitted pain as such, rather than in a specific type of headache as was suggested for cluster headache.

Cortical astrocytes rewire somatosensory cortical circuits for peripheral neuropathic pain

Long-term treatments to ameliorate peripheral neuropathic pain that includes mechanical allodynia are limited. While glial activation and altered nociceptive transmission within the spinal cord are associated with the pathogenesis of mechanical allodynia, changes in cortical circuits also accompany peripheral nerve injury and may represent additional therapeutic targets. Dendritic spine plasticity in the S1 cortex appears within days following nerve injury; however, the underlying cellular mechanisms of this plasticity and whether it has a causal relationship to allodynia remain unsolved. Furthermore, it is not known whether glial activation occurs within the S1 cortex following injury or whether it contributes to this S1 synaptic plasticity. Using in vivo 2-photon imaging with genetic and pharmacological manipulations of murine models, we have shown that sciatic nerve ligation induces a re-emergence of immature metabotropic glutamate receptor 5 (mGluR5) signaling in S1 astroglia, which elicits spontaneous somatic Ca2+ transients, synaptogenic thrombospondin 1 (TSP-1) release, and synapse formation. This S1 astrocyte reactivation was evident only during the first week after injury and correlated with the temporal changes in S1 extracellular glutamate levels and dendritic spine turnover. Blocking the astrocytic mGluR5-signaling pathway suppressed mechanical allodynia, while activating this pathway in the absence of any peripheral injury induced long-lasting (>1 month) allodynia. We conclude that reawakened astrocytes are a key trigger for S1 circuit rewiring and that this contributes to neuropathic mechanical allodynia.

Central Sensitization in Knee Osteoarthritis: Relating Presurgical Brainstem Neuroimaging and PainDETECT-Based Patient Stratification to Arthroplasty Outcome

OBJECTIVE

The neural mechanisms of pain in knee osteoarthritis (OA) are not fully understood, and some patients have neuropathic-like pain associated with central sensitization. To address this, we undertook the present study in order to identify central sensitization using neuroimaging and PainDETECT and to relate it to postarthroplasty outcome.

METHODS

Patients awaiting arthroplasty underwent quantitative sensory testing, psychological assessment, and functional magnetic resonance imaging (fMRI). Neuroimaging (fMRI) was conducted during punctate stimulation (n = 24) and cold stimulation (n = 20) to the affected knee. The postoperative outcome was measured using the Oxford Knee Score, patient-reported moderate-to-severe long-term pain postarthroplasty, and a range of pain-related questionnaires.

RESULTS

Patients with neuropathic-like pain presurgery (identified using PainDETECT; n = 14) reported significantly higher pain in response to punctate stimuli and cold stimuli near the affected joint (P < 0.05). Neural activity in these patients, compared to those without neuropathic-like pain, was significantly lower in the rostral anterior cingulate cortex (P < 0.05) and higher in the rostral ventromedial medulla (RVM) during punctate stimulation (P < 0.05), with significant functional connectivity between these two areas (r = 0.49, P = 0.018). Preoperative neuropathic-like pain and higher neural activity in the RVM were associated with moderate-to-severe long-term pain after arthroplasty (P = 0.0356).

CONCLUSION

The psychophysical and neuroimaging data suggest that a subset of OA patients have centrally mediated pain sensitization. This was likely due to supraspinally mediated reductions in inhibition and increases in facilitation of nociceptive signaling, and was associated with a worse outcome following arthroplasty. The neurobiologic confirmation of central sensitization in patients with features of neuropathic pain, identified using PainDETECT, provides further support for the investigation of such bedside measures for patient stratification, to better predict postsurgical outcomes.

Experimental brush-evoked allodynia activates posterior parietal cortex

OBJECTIVE

To study the brain activation pattern of coexisting experimental ongoing pain and brush-evoked allodynia (pain evoked by innocuous brush) with the use of PET.

BACKGROUND

Neuropathic pain usually has two essential phenomena: ongoing pain and brush-evoked allodynia, which coexist and may influence each other. Capsaicin induces both ongoing pain and brush-evoked allodynia.

METHODS

Eight healthy right-handed volunteers participated in eight H2(15)O PET scans with two blocks of four randomized conditions: 1) rest, 2) brush, 3) capsaicin pain, and 4) capsaicin pain + brush (brush-evoked allodynia). Capsaicin was injected intradermally on the nondominant forearm and the subjects rated pain intensity and unpleasantness on 100-mm visual analogue scales.

RESULTS

Pain intensity and unpleasantness were significantly higher during brush-evoked allodynia (74 +/- 4 and 67 +/- 4 mm) compared with capsaicin pain alone (60 +/- 4 and 51 +/- 5 mm). Brush-evoked allodynia, but not capsaicin pain alone, increased blood flow significantly in the contralateral right sensory association cortex Brodmann area (BA) 5/7, and in bilateral prefrontal cortex BA 9/10/47 and insula. No significant activity was seen in thalamus or primary somatosensory cortex (SI). Direct comparison between capsaicin pain and brush-evoked allodynia revealed significant increase in contralateral BA 5/7 only.

CONCLUSIONS

The specific activation of contralateral BA 5/7 indicates that this brain region is important to the processing of brush-evoked allodynia. The involvement of BA 5/7 in brush-evoked allodynia is claimed to reflect multisensory input to this region, its role in conscious pain perception, and its neuroplastic properties.

Pudendal neuralgia: CT-guided pudendal nerve block technique

Chronic anoperineal pain without any apparent etiology may be caused by compression of the pudendal nerve. This presentation illustrates the course of the pudendal nerve and the technique of computed tomography-guided infiltration of the nerve.

Radiation exposure of the spinal interventionalist performing fluoroscopically guided lumbar transforaminal epidural steroid injections

OBJECTIVE

To evaluate radiation exposure to spinal interventionalists while performing transforaminal epidural steroid injections (TFESIs).

DESIGN

Prospective study.

SETTING

Multidisciplinary spine center.

PARTICIPANTS

One hundred consecutive patients with either herniated nucleus pulposus (HNP) or lumbar spinal stenosis (LSS).

INTERVENTION

Fluroscopically guided lumbar TFESIs.

MAIN OUTCOME MEASURE

Radiation exposure was monitored by radiography technologists who allocated 4 dosimetry badges to all spinal interventionalists performing fluroscopically guided lumbar TFESIs on patients being treated for radicular pain. Badges were placed on the ring finger, glasses, and the inside and outside of the lead apron worn by the interventionalists. The radiography technologists also wore marked badges outside their lead aprons. One control badge was placed 67in away from the fluoroscopy table and a second badge was placed in a desk more than 500ft away from the procedure to monitor ambient radiation.

RESULTS

The average fluoroscopy time per procedure was 15.16 seconds. The average exposure per procedure was 0.7mrem at the ring badge, 0.4mrem at the glasses badge, and 0.3mrem at the outside apron badge. No radiation was detectable at the inside apron or at the outside room control badge. The cumulative exposure to the interventionalists from all 100 procedures was 70mrem at the ring badge, 40mrem at the glasses badge, and 30mrem at the outside apron badge. The radiography technologists' average exposure during these procedures was below the limit of detectablility. Radiation time under fluoroscopy ranged from 5 to 38 seconds. The interventionalist's exposure to radiation was significantly greater during procedures conducted on patients with LSS then during procedures on patients with HNP.

CONCLUSION

Adhering to a radiation safety program that includes maximizing the distance the spinal interventionalist is from the radiation source, decreasing exposure time, and proper shielding is essential when performing fluoroscopically guided lumbar TFESIs. Our study shows that exposure to radiation of the spinal interventionalist performing fluoroscopically guided lumbar TFESIs was well within safety limits when proper techniques were followed.

The role of cortex in central pain syndromes: preliminary results of a long-term technetium-99 hexamethylpropyleneamineoxime single photon emission computed tomography study

The role of the somatosensory cortex in central pain syndromes is widely questioned. Two recent position emission tomography studies detected a strong activation of the parietal and cingular cortices after brief nociceptive stimuli. On the other hand, a recent single photon emission computed tomography study found no cortical activation in five patients affected by central poststroke pain and algodystrophia. In this study, we present the single photon emission computed tomography findings in five patients suffering from central pain syndromes. Two of these, one with facial postrhizotomy anesthesia dolorosa and the other with central poststroke pain, showed a decrease of blood flow in the parietal lobe, further decreasing after stimulation by nonpainful maneuvers. Our results suggest that somatosensory cortical areas might be involved in the generation of anomalous pain states in some cases of central pain syndromes.

Ultrasound in the detection and treatment of a painful stump neuroma

Ultrasound is an established modality for the evaluation of neuromas, particularly Morton's neuromas. It has also had success in the assessment of amputation stump neuromas. While ultrasound localization for steroid injection has proven useful in the conservative treatment of Morton's neuromas, it has not yet been established as a localization technique for steroid injection to successfully treat amputation stump neuromas.

Visualizing Nerve Injury in a Neuropathic Pain Model with [18F]FTC-146 PET/MRI

The ability to locate nerve injury and ensuing neuroinflammation would have tremendous clinical value for improving both the diagnosis and subsequent management of patients suffering from pain, weakness, and other neurologic phenomena associated with peripheral nerve injury. Although several non-invasive techniques exist for assessing the clinical manifestations and morphological aspects of nerve injury, they often fail to provide accurate diagnoses due to limited specificity and/or sensitivity. Herein, we describe a new imaging strategy for visualizing a molecular biomarker of nerve injury/neuroinflammation, i.e., the sigma-1 receptor (S1R), in a rat model of nerve injury and neuropathic pain. The two-fold higher increase of S1Rs was shown in the injured compared to the uninjured nerve by Western blotting analyses. With our novel S1R-selective radioligand, [18F]FTC-146 (6-(3-[18F]fluoropropyl)-3-(2-(azepan-1-yl)ethyl)benzo[d]thiazol-2(3H)-one), and positron emission tomography-magnetic resonance imaging (PET/MRI), we could accurately locate the site of nerve injury created in the rat model. We verified the accuracy of this technique by ex vivo autoradiography and immunostaining, which demonstrated a strong correlation between accumulation of [18F]FTC-146 and S1R staining. Finally, pain relief could also be achieved by blocking S1Rs in the neuroma with local administration of non-radioactive [19F]FTC-146. In summary, [18F]FTC-146 S1R PET/MR imaging has the potential to impact how we diagnose, manage and treat patients with nerve injury, and thus warrants further investigation.

Gabapentin dose and the 30-day risk of altered mental status in older adults: A retrospective population-based study

Gabapentin is an effective treatment for chronic neuropathic pain but may cause dizziness, drowsiness, and confusion in some older adults. The goal of this study was to assess the association between gabapentin dosing and adverse outcomes by obtaining estimates of the 30-day risk of hospitalization with altered mental status and mortality in older adults (mean age 76 years) in Ontario, Canada initiated on high dose (>600 mg/day; n = 34,159) compared to low dose (≤600 mg/day; n = 76,025) oral gabapentin in routine outpatient care. A population-based, retrospective cohort study assessing new gabapentin use between 2002 to 2014 was conducted. The primary outcome was 30-day hospitalization with an urgent head computed tomography (CT) scan in the absence of evidence of stroke (a proxy for altered mental status). The secondary outcome was 30-day all-cause mortality. The baseline characteristics measured in the two dose groups were similar. Initiation of a high versus low dose of gabapentin was associated with a higher risk of hospitalization with head CT scan (1.27% vs. 1.06%, absolute risk difference 0.21%, adjusted relative risk 1.29 [95% CI 1.14 to 1.46], number needed to treat 477) but not a statistically significant higher risk of mortality (1.25% vs. 1.16%, absolute risk difference of 0.09%, adjusted relative risk of 1.01 [95% CI 0.89 to 1.14]). Overall, the risk of being hospitalized with altered mental status after initiating gabapentin remains low, but may be reduced through the judicious use of gabapentin, use of the lowest dose to control pain, and vigilance for early signs of altered mental status.

Activation of the dorsal, but not the ventral, hippocampus relieves neuropathic pain in rodents

ABSTRACT

Accumulating evidence suggests hippocampal impairment under the chronic pain phenotype. However, it is unknown whether neuropathic behaviors are related to dysfunction of the hippocampal circuitry. Here, we enhanced hippocampal activity by pharmacological, optogenetic, and chemogenetic techniques to determine hippocampal influence on neuropathic pain behaviors. We found that excitation of the dorsal (DH), but not the ventral (VH) hippocampus induces analgesia in 2 rodent models of neuropathic pain (SNI and SNL) and in rats and mice. Optogenetic and pharmacological manipulations of DH neurons demonstrated that DH-induced analgesia was mediated by N-Methyl-D-aspartate and μ-opioid receptors. In addition to analgesia, optogenetic stimulation of the DH in SNI mice also resulted in enhanced real-time conditioned place preference for the chamber where the DH was activated, a finding consistent with pain relief. Similar manipulations in the VH were ineffective. Using chemo-functional magnetic resonance imaging (fMRI), where awake resting-state fMRI was combined with viral vector-mediated chemogenetic activation (PSAM/PSEM89s) of DH neurons, we demonstrated changes of functional connectivity between the DH and thalamus and somatosensory regions that tracked the extent of relief from tactile allodynia. Moreover, we examined hippocampal functional connectivity in humans and observe differential reorganization of its anterior and posterior subdivisions between subacute and chronic back pain. Altogether, these results imply that downregulation of the DH circuitry during chronic neuropathic pain aggravates pain-related behaviors. Conversely, activation of the DH reverses pain-related behaviors through local excitatory and opioidergic mechanisms affecting DH functional connectivity. Thus, this study exhibits a novel causal role for the DH but not the VH in controlling neuropathic pain-related behaviors.

Occipital neuralgia secondary to exuberant callus formation. Case report

The authors report the case of a 78-year-old woman suffering from right occipital neuralgia in whom computerized tomography and magnetic resonance images demonstrated an irregular bone mass in the C-2 vertebral body. This "bone tumor" happened to be an exuberant callus formation that arose as a result of a previous axis body fracture. The patient's occipital pain was immediately relieved after she underwent C2-3 root release.

C-arm-guided pudendal nerve block: a new technique

Pudendal nerve block (PNB) is an effective diagnostic and/or treatment method for perineal pain. Various approach techniques, such as transperineal, transvaginal, computerised tomography (CT)- or sono-guided approach, have been suggested for this block. However, they have some limitations, such as high cost, difficulty to perform in practice, inaccurate and unreliable results and inconvenience. To overcome these limitations, we first tried C-arm-guided approach for accomplishing PNB in the prone position. Under the optimal ischial spine view of C-arm fluoroscopy, the block needle was placed on the tip of the ischial spine. Then a mixed solution for the block was administered. All of the 25 patients enrolled in this study were blocked successfully using this method. No side-effects or complications were observed in relation to the block. We concluded that the C-arm-guided approach for PNB is an effective alternative to the existing techniques, which can overcome their limitations.

Spinal fMRI reveals decreased descending inhibition during secondary mechanical hyperalgesia

Mechanical hyperalgesia is one distressing symptom of neuropathic pain which is explained by central sensitization of the nociceptive system. This sensitization can be induced experimentally with the heat/capsaicin sensitization model. The aim was to investigate and compare spinal and supraspinal activation patterns of identical mechanical stimulation before and after sensitization using functional spinal magnetic resonance imaging (spinal fMRI). Sixteen healthy subjects (6 female, 10 male, mean age 27.2 ± 4.0 years) were investigated with mechanical stimulation of the C6 dermatome of the right forearm during spinal fMRI. Testing was always performed in the area outside of capsaicin application (i.e. area of secondary mechanical hyperalgesia). During slightly noxious mechanical stimulation before sensitization, activity was observed in ipsilateral dorsolateral pontine tegmentum (DLPT) which correlated with activity in ipsilateral spinal cord dorsal gray matter (dGM) suggesting activation of descending nociceptive inhibition. During secondary mechanical hyperalgesia, decreased activity was observed in bilateral DLPT, ipsilateral/midline rostral ventromedial medulla (RVM), and contralateral subnucleus reticularis dorsalis, which correlated with activity in ipsilateral dGM. Comparison of voxel-based activation patterns during mechanical stimulation before/after sensitization showed deactivations in RVM and activations in superficial ipsilateral dGM. This study revealed increased spinal activity and decreased activity in supraspinal centers involved in pain modulation (SRD, RVM, DLPT) during secondary mechanical hyperalgesia suggesting facilitation of nociception via decreased endogenous inhibition. Results should help prioritize approaches for further in vivo studies on pain processing and modulation in humans.

Dimensions of the lumbar spinal canal: variations and correlations with somatometric parameters using CT

The aim of this study was to investigate the correlation of vertebral dimensions with somatometric parameters in patients without clinical symptoms and radiological signs of central lumbar spinal stenosis. One hundred patients presenting with low back pain or sciatica were studied with CT. In each of the L3, L4 and L5 vertebra three slices were taken with the following measurements: 1. Slice through the intervertebral disc: (a) spinal canal area; (b) interarticular diameter; (c) interligamentous diameter. 2. Slice below the vertebral arcus: (a) dural sac area; (b) vertebral body area. 3. Pediculolaminar level: (a) anteroposterior diameter and interpedicular diameter of the spinal canal; (b) spinal canal area; (c) width of the lateral recesses. The Jones-Thomson index was also estimated. The results of the present study showed that there is a statistically significant correlation of height, weight and age with various vertebral indices. The conventional, widely accepted, anteroposterior diameter of 11.5 mm of the lumbar spinal canal is independent of somatometric parameters, and it is the only constant measurement for the estimation of lumbar spinal stenosis with a single value. The present study suggests that there are variations of the dimensions of the lumbar spinal canal and correlations with height, weight and age of the patient.

Uncommon areas of electrical stimulation for pain relief

Uncommon stimulation refers to the use of peripheral nerve and spinal cord stimulation for nontraditional applications. There has been much interest recently with subcutaneous suboccipital stimulation for occipital neuralgia, sacral stimulation for pelvic pain, trigeminal stimulation for trigeminal neuralgia, and spinal cord stimulation for angina and peripheral ischemia. The indications and techniques used for accomplishing each method are discussed.

Anorectal function and morphology in patients with sporadic proctalgia fugax

PURPOSE

The pathophysiology of sporadic proctalgia fugax remains unknown. This study investigates whether patients with this syndrome exhibit alterations in anal function and morphology.

METHODS

Eighteen patients with sporadic proctalgia fugax and 18 sex-matched and age-matched healthy controls were studied. Manometric studies investigated anal resting and squeeze pressures, the rectoanal inhibitory reflex, rectal compliance, and smooth muscle response to edrophonium chloride administration. External and internal sphincter thickness was measured endosonographically.

RESULTS

Patients had slightly higher (P = 0.0291) anal resting pressures (65.5 +/- 11.4 mmHg) than controls (56 +/- 9.9 mmHg). However, anal squeeze pressure, sphincter relaxation during rectal distention, and rectal compliance were similar in both groups, and no alterations were detected in external and internal anal sphincter thickness. Edrophonium chloride administration was followed by sharp postrelaxation contractions in two patients, whereas anal function remained unaltered in controls. Acute episodes of proctalgia, which occurred in two patients while under study, were associated with a rise in anal resting tone and an increase in slow wave amplitude.

CONCLUSIONS

In the resting state, patients with proctalgia fugax have normal anorectal function and morphology. However, they may exhibit a motor abnormality of the anal smooth muscle during an acute attack.

Ischemic osteonecrosis under fixed partial denture pontics: radiographicand microscopic features in 38 patients with chronic pain

STATEMENT OF PROBLEM

Previous studies have identified focal areas of alveolar tenderness, elevated mucosal temperature, radiographic abnormality, and increased radioisotope uptake or "hot spots" within the quadrant of pain in most patients with chronic, idiopathic facial pain (phantom pain, atypical facial neuralgia, and atypical facial pain).

PURPOSE

This retrospective investigation radiographically and microscopically evaluated intramedullary bone in a certain subset of patients with histories of endodontics, extraction, and fixed partial denture placement in an area of "idiopathic" pain.

MATERIAL AND METHODS

Patients from 12 of the United States were identified through tissue samples, histories, and radiographs submitted to a national biopsy service. Imaging tests, coagulation tests, and microscopic features were reviewed. Of 38 consecutive idiopathic facial pain patients, 32 were women.

RESULTS

Approximately 90% of subpontic bone demonstrated either ischemic osteonecrosis (68%), chronic osteomyelitis (21%), or a combination (11%). More than 84% of the patients had abnormal radiographic changes in subpontic bone, and 5 of 9 (56%) patients who underwent radioisotope bone scan revealed hot spots in the region. Of the 14 patients who had laboratory testing for coagulation disorders, 71% were positive for thrombophilia, hypofibrinolysis, or both (normal: 2% to 7%). Ten pain-free patients with abnormal subpontic bone on radiographs were also reviewed.

CONCLUSIONS

Intraosseous ischemia and chronic inflammation were suggested as a pathoetiologic mechanism for at least some patients with atypical facial pain. These conditions were also offered as an explanation for poor healing of extraction sockets and positive radioisotope scans.

Meralgia paresthetica caused by hip-huggers in a patient with aberrant course of the lateral femoral cutaneous nerve

"Hip-huggers" may be a precipitating factor for meralgia paresthetica (MP), especially in thin persons with an aberrant pathway of the lateral femoral cutaneous nerve (LFCN). We describe a 25-year-old woman with a long-standing history of MP caused by an abnormal course of the LFCN and tight trousers, specifically hip-huggers. Ultrasonography was useful for detecting the lesion site and the abnormal pathway of the LFCN. After neurectomy of the LFCN, most of the symptoms of MP were relieved, but mild hypesthesia remained in the lateral thigh.

Pain modulation by intranasal oxytocin and emotional picture viewing - a randomized double-blind fMRI study

The hormone oxytocin has been hypothesized to influence the emotional dimension of pain. This randomized, placebo-controlled, double-blind, crossover study explored whether intranasal oxytocin and emotional context can affect heat pain perception in 30 healthy male volunteers. After receiving 36 IU oxytocin or placebo, participants underwent functional Magnetic Resonance Imaging (fMRI) during which noxious and non-noxious thermode heat stimuli were applied. Simultaneously, scenes from the International Affective Pictures System (IAPS) with positive, neutral, and negative emotional valence were shown. Heat intensity and unpleasantness ratings were obtained. The activity of whole-brain correlates of heat processing was quantified via multi-voxel pattern analysis. We observed no appreciable main effects of oxytocin on ratings or neural pain correlates. Effects of emotional picture valence on ratings were smaller than reported in previous studies. Nevertheless, oxytocin was found to significantly enhance the influence of picture valence on unpleasantness ratings at noxious heat levels. No corresponding changes in whole-brain correlates of heat intensity processing were found. Our study provides evidence that intranasal oxytocin increases the effects of emotional context on the subjective unpleasantness of experimental heat pain. Future studies are needed to determine whether this effect can be utilized in clinical settings.

Supraspinal nociceptive networks in neuropathic pain after spinal cord injury

Neuropathic pain following spinal cord injury involves plastic changes along the whole neuroaxis. Current neuroimaging studies have identified grey matter volume (GMV) and resting-state functional connectivity changes of pain processing regions related to neuropathic pain intensity in spinal cord injury subjects. However, the relationship between the underlying neural processes and pain extent, a complementary characteristic of neuropathic pain, is unknown. We therefore aimed to reveal the neural markers of widespread neuropathic pain in spinal cord injury subjects and hypothesized that those with greater pain extent will show higher GMV and stronger connectivity within pain related regions. Thus, 29 chronic paraplegic subjects and 25 healthy controls underwent clinical and electrophysiological examinations combined with neuroimaging. Paraplegics were demarcated based on neuropathic pain and were thoroughly matched demographically. Our findings indicate that (a) spinal cord injury subjects with neuropathic pain display stronger connectivity between prefrontal cortices and regions involved with sensory integration and multimodal processing, (b) greater neuropathic pain extent, is associated with stronger connectivity between the posterior insular cortex and thalamic sub-regions which partake in the lateral pain system and (c) greater intensity of neuropathic pain is related to stronger connectivity of regions involved with multimodal integration and the affective-motivational component of pain. Overall, this study provides neuroimaging evidence that the pain phenotype of spinal cord injury subjects is related to the underlying function of their resting brain.

Neuropathic Pain: Biomolecular Intervention and Imaging via Targeting Microglia Activation

Many diseases, including cancer, can lead to neuropathic pain (NP). NP is one of the accompanying symptoms of suffering in many conditions and the life quality of NP patient is seriously affected. Due to complex causes, the effects of clinical treatments have been very unsatisfactory. Many experts have found that neuron-microglia interaction plays an essential role in NP occurrence and development. Therefore, the activation of microglia, related inflammatory mediators and molecular and cellular signaling pathways have become the focus of NP research. With the help of modern functional imaging technology, advanced pre-and clinical studies have been carried out and NP interventions have been attempted by using the different pharmaceuticals and the extracted active components of various traditional herbal medicines. In this communication, we review the mechanism of microglia on NP formation and treatment and molecular imaging technology's role in the clinical diagnosis and evaluation of NP therapies.

Sonographic evaluation of the greater occipital nerve in unilateral occipital neuralgia

OBJECTIVES

Occipital neuralgia is a headache that may result from greater occipital nerve entrapment. Entrapped peripheral nerves typically have an increase in cross-sectional area. The purpose of this study was to measure the cross-sectional area and circumference of symptomatic and asymptomatic greater occipital nerves in patients with unilateral occipital neuralgia and to correlate the greater occipital nerve cross-sectional area with headache severity, sex, and body mass index.

METHODS

Both symptomatic and contralateral asymptomatic greater occipital nerve cross-sectional areas and circumferences were measured by a single examiner using sonography in 17 patients. The Wilcoxon signed rank test and Spearman rank order correlation coefficient were used to analyze the data.

RESULTS

Significant differences between the cross-sectional areas and circumferences of the symptomatic and asymptomatic greater occipital nerves were noted (P < .001). No difference existed in cross-sectional area (P = .40) or circumference (P = .10) measurements of the nerves between male and female patients. A significant correlation existed between the body mass index and symptomatic (r = 0.424; P = .045) and asymptomatic (r = 0.443; P = .037) cross-sectional areas. There was no correlation shown between the cross-sectional area of the symptomatic nerve and the severity of Headache Impact Test 6 scores (r = -0.342; P = .179).

CONCLUSIONS

We report sonographic evidence showing an increased cross-sectional area and circumference of the symptomatic greater occipital nerve in patients with unilateral occipital neuralgia.