Numbness in clinical and experimental pain – A cross-sectional study exploring the mechanisms of reduced tactile function

Indication for spinal sensitization in chronic low back pain: mechanical hyperalgesia adjacent to but not within the most painful body area

Introduction

In 85% of patients with chronic low back pain (CLBP), no specific pathoanatomical cause can be identified. Besides primary peripheral drivers within the lower back, spinal or supraspinal sensitization processes might contribute to the patients' pain.

Objectives

The present study conceptualized the most painful area (MP) of patients with nonspecific CLBP as primarily affected area and assessed signs of peripheral, spinal, and supraspinal sensitization using quantitative sensory testing (QST) in MP, a pain-free area adjacent to MP (AD), and a remote, pain-free control area (CON).

Methods

Fifty-nine patients with CLBP (51 years, SD = 16.6, 22 female patients) and 35 pain-free control participants individually matched for age, sex, and testing areas (49 years, SD = 17.5, 19 female participants) underwent a full QST protocol in MP and a reduced QST protocol assessing sensory gain in AD and CON. Quantitative sensory testing measures, except paradoxical heat sensations and dynamic mechanical allodynia (DMA), were Z-transformed to the matched control participants and tested for significance using Z-tests (α = 0.001). Paradoxical heat sensations and DMA occurrence were compared between cohorts using Fisher's exact tests (α = 0.05). The same analyses were performed with a high-pain and a low-pain CLBP subsample (50% quantile).

Results

Patients showed cold and vibration hypoesthesia in MP (all Ps < 0.001) and mechanical hyperalgesia (P < 0.001) and more frequent DMA (P = 0.044) in AD. The results were mainly driven by the high-pain CLBP subsample. In CON, no sensory alterations were observed.

Conclusion

Mechanical hyperalgesia and DMA adjacent to but not within MP, the supposedly primarily affected area, might reflect secondary hyperalgesia originating from spinal sensitization in patients with CLBP.

Visuotactile integration in individuals with fibromyalgia

Our brain constantly integrates afferent information, such as visual and tactile information, to perceive the world around us. According to the maximum-likelihood estimation (MLE) model, imprecise information will be weighted less than precise, making the multisensory percept as precise as possible. Individuals with fibromyalgia (FM), a chronic pain syndrome, show alterations in the integration of tactile information. This could lead to a decrease in their weight in a multisensory percept or a general disruption of multisensory integration, making it less beneficial. To assess multisensory integration, 15 participants with FM and 18 pain-free controls performed a temporal-order judgment task in which they received pairs of sequential visual, tactile (unisensory conditions), or visuotactile (multisensory condition) stimulations on the index and the thumb of the non-dominant hand and had to determine which finger was stimulated first. The task enabled us to measure the precision and accuracy of the percept in each condition. Results indicate an increase in precision in the visuotactile condition compared to the unimodal conditions in controls only, although we found no intergroup differences. The observed visuotactile precision was correlated to the precision predicted by the MLE model in both groups, suggesting an optimal integration. Finally, the weights of the sensory information were not different between the groups; however, in the group with FM, higher pain intensity was associated with smaller tactile weight. This study shows no alterations of the visuotactile integration in individuals with FM, though pain may influence tactile weight in these participants.

Sex moderates the association between quantitative sensory testing and acute and chronic pain after total knee/hip arthroplasty

OBJECTIVES

Acute postsurgical pain (APSP) may persist over time and become chronic. Research on predictors for APSP and chronic postsurgical pain (CPSP) has produced inconsistent results. This observational study aimed to analyze psychological and psychophysical variables associated with APSP and CPSP after total knee or hip arthroplasty, and to explore the role of sex.

METHODS

Assessments were conducted before surgery, 48 h, and 3 months postsurgery, including questionnaires (sociodemographic, pain related, and psychological) and quantitative sensory testing (QST). Hierarchical linear regression models analyzed potential predictors of APSP and CPSP, and moderation analyses evaluated the role of sex.

RESULTS

The study included 63 participants undergoing total knee (34, 54%) or hip (29, 46%) arthroplasty. Thirty-one (49.2%) were female and 32 (50.8%) were male. APSP (48 h) was associated with impaired conditioned pain modulation (CPM) (β = 0.301, p = 0.019). CPSP (3 months) was associated with being female (β = 0.282, p = 0.029), longer presurgical pain duration (β = 0.353, p = 0.006), knee arthroplasty (β = -0.312, p = 0.015), higher APSP intensity (β = 373, p = 0.004), and impaired CPM (β = 0.126, p = 0.004). In multivariate analysis, these clinical variables were significant predictors of CPSP, unlike sex, and CPM (adj. R 2 = 0.349). Moderation analyses showed that wind-up ratio (WUR) was a significant predictor of APSP in men (WUR × sex: b = -1.373, p = 0.046) and CPM was a significant predictor of CPSP in women (CPM × sex: b = 1.625, p = 0.016).

CONCLUSIONS

Specific QST parameters could identify patients at risk for high-intensity APSP and CPSP, with sex as a moderator. This has important clinical implications for patient care, paving the way for developing tailored preventive pain management strategies.

Sensory phenotypes in complex regional pain syndrome and chronic low back pain-indication of common underlying pathomechanisms

Introduction

First-line pain treatment is unsatisfactory in more than 50% of chronic pain patients, likely because of the heterogeneity of mechanisms underlying pain chronification.

Objectives

This cross-sectional study aimed to better understand pathomechanisms across different chronic pain cohorts, regardless of their diagnoses, by identifying distinct sensory phenotypes through a cluster analysis.

Methods

We recruited 81 chronic pain patients and 63 age-matched and sex-matched healthy controls (HC). Two distinct chronic pain cohorts were recruited, ie, complex regional pain syndrome (N = 20) and low back pain (N = 61). Quantitative sensory testing (QST) was performed in the most painful body area to investigate somatosensory changes related to clinical pain. Furthermore, QST was conducted in a pain-free area to identify remote sensory alterations, indicating more widespread changes in somatosensory processing.

Results

Two clusters were identified based on the QST measures in the painful area, which did not represent the 2 distinct pain diagnoses but contained patients from both cohorts. Cluster 1 showed increased pain sensitivities in the painful and control area, indicating central sensitization as a potential pathomechanism. Cluster 2 showed a similar sensory profile as HC in both tested areas. Hence, either QST was not sensitive enough and more objective measures are needed to detect sensitization within the nociceptive neuraxis or cluster 2 may not have pain primarily because of sensitization, but other factors such as psychosocial ones are involved.

Conclusion

These findings support the notion of shared pathomechanisms irrespective of the pain diagnosis. Conversely, different mechanisms might contribute to the pain of patients with the same diagnosis.

Tactile acuity improves during acute experimental pain of the limb

Introduction

Chronic pain is associated with poor tactile acuity, commonly measured with the 2-point discrimination (TPD) test. Although poor tactile acuity across chronic pain conditions is well established, less is known in acute pain.

Objective

Recent conflicting findings in experimentally induced neck and back pain led us to conduct a TPD investigation in experimentally induced limb pain. We hypothesised altered TPD during experimental upper limb pain, but we did not speculate on the direction of the change.

Methods

Thirty healthy subjects immersed their dominant hand in a circulating cold-water bath at 7°C (cold pressor test [CPT]). Two-point discrimination was measured at baseline (pre-CPT), during pain (during-CPT), and after withdrawal from the water (post-CPT) in 3 different sites: (1) the dominant forearm, (2) dominant arm and (3) contralateral forearm.

Results

Repeated-measures analysis of variance revealed a significant main effect of time (F(2,56) = 4.45, P = 0.02, η p 2 = 0.14) on TPD; in all 3 sites, TPD values decreased (ie, tactile acuity improved) during pain. Interestingly, the contralateral forearm followed a similar pattern to the dominant (ie, painful) forearm, and furthermore was the only site that exhibited any correlation with pain, albeit in an intriguing direction (r = 0.57, P = 0.001), ie, the greater the pain the worse the tactile acuity.

Conclusion

The improvements in tactile acuity during experimentally induced limb pain may reflect a protective response. The changes in the corresponding site in the contralateral limb may reflect a protective spinal cross talk. Such a response, together with the interesting relationship between tactile acuity and pain, warrant further inquiry.

Recommendations for terminology and the identification of neuropathic pain in people with spine-related leg pain. Outcomes from the NeuPSIG working group

ABSTRACT

Pain radiating from the spine into the leg is commonly referred to as "sciatica," "Sciatica" may include various conditions such as radicular pain or painful radiculopathy. It may be associated with significant consequences for the person living with the condition, imposing a reduced quality of life and substantial direct and indirect costs. The main challenges associated with a diagnosis of "sciatica" include those related to the inconsistent use of terminology for the diagnostic labels and the identification of neuropathic pain. These challenges hinder collective clinical and scientific understanding regarding these conditions. In this position paper, we describe the outcome of a working group commissioned by the Neuropathic Pain Special Interest Group (NeuPSIG) of the International Association for the Study of Pain (IASP) which was tasked with the following objectives: (1) to revise the use of terminology for classifying spine-related leg pain and (2) to propose a way forward on the identification of neuropathic pain in the context of spine-related leg pain. The panel recommended discouraging the term "sciatica" for use in clinical practice and research without further specification of what it entails. The term "spine-related leg pain" is proposed as an umbrella term to include the case definitions of somatic referred pain and radicular pain with and without radiculopathy. The panel proposed an adaptation of the neuropathic pain grading system in the context of spine-related leg pain to facilitate the identification of neuropathic pain and initiation of specific management in this patient population.

Somatosensory and trigeminal pathway abnormalities in Chinese patients with trigeminal neuralgia

This study aimed to evaluate somatosensory function in Chinese patients with trigeminal neuralgia (TN) using a standard quantitative sensory testing (QST) battery and electrophysiological tests consisting of contact heat-evoked potentials (CHEPs) and blink reflex (BR). Twenty patients with TN and 20 sex- and age-matched healthy controls were recruited for this study. A standard QST protocol recommended by the German Research Network on Neuropathic Pain was carried out on the patients' painful and contralateral faces, the controls' right faces, and all participants' right hands. The CHEPs and BR were recorded at the Cz electrode and bilateral lower bellies of the orbicularis oculi, respectively, with thermal stimuli applied to both sides of the patient's face and the control's right face. The cold detection threshold, heat pain threshold, and mechanical pain threshold on the painful face were lower than those of healthy controls (P < 0.05), whereas the cold pain threshold and mechanical detection threshold were higher (P < 0.05) on the painful faces than those of the contralateral faces from patients or healthy controls. Mechanical pain sensitivity was higher in both test sites than in healthy controls (P < 0.05). Significantly longer N latencies (P < 0.05) and lower N-P amplitudes (P < 0.01) were detected in the patients' painful sites than in the contralateral sites and those of healthy controls. Comprehensive somatosensory abnormalities were found in painful facial sites in patients with TN, suggesting disturbances in the processing of somatosensory stimuli. Deficiencies in electrophysiological tests further revealed unilaterally impaired function of the trigeminal pathway in TN patients.

Nerve pathology and neuropathic pain after whiplash injury: a systematic review and meta-analysis

ABSTRACT

There is no clear understanding of the mechanisms causing persistent pain in patients with whiplash-associated disorder (WAD). The aim of this systematic review was to assess the evidence for nerve pathology and neuropathic pain in patients with WAD. EMBASE, PubMed, CINAHL (EBSCO), and MEDLINE were searched from inception to September 1, 2020. Study quality and risk of bias were assessed using the Newcastle-Ottawa Quality Assessment Scales. Fifty-four studies reporting on 390,644 patients and 918 controls were included. Clinical questionnaires suggested symptoms of predominant neuropathic characteristic in 34% of patients (range 25%-75%). The mean prevalence of nerve pathology detected with neurological examination was 13% (0%-100%) and 32% (10%-100%) with electrodiagnostic testing. Patients independent of WAD severity (Quebec Task Force grades I-IV) demonstrated significantly impaired sensory detection thresholds of the index finger compared with controls, including mechanical (SMD 0.65 [0.30; 1.00] P < 0.005), current (SMD 0.82 [0.25; 1.39] P = 0.0165), cold (SMD -0.43 [-0.73; -0.13] P = 0.0204), and warm detection (SMD 0.84 [0.25; 1.42] P = 0.0200). Patients with WAD had significantly heightened nerve mechanosensitivity compared with controls on median nerve pressure pain thresholds (SMD -1.10 [-1.50; -0.70], P < 0.0001) and neurodynamic tests (SMD 1.68 [0.92; 2.44], P = 0.0004). Similar sensory dysfunction and nerve mechanosensitivity was seen in WAD grade II, which contradicts its traditional definition of absent nerve involvement. Our findings strongly suggest a subset of patients with WAD demonstrate signs of peripheral nerve pathology and neuropathic pain. Although there was heterogeneity among some studies, typical WAD classifications may need to be reconsidered and include detailed clinical assessments for nerve integrity.

The sensorimotor theory of pathological pain revisited

Harris (1999) proposed that pain can arise in the absence of tissue damage because changes in the cortical representation of the painful body part lead to incongruences between motor intention and sensory feedback. This idea, subsequently termed the sensorimotor theory of pain, has formed the basis for novel treatments for pathological pain. Here we review the evidence that people with pathological pain have changes to processes contributing to sensorimotor function: motor function, sensory feedback, cognitive representations of the body and its surrounding space, multisensory processing, and sensorimotor integration. Changes to sensorimotor processing are most evident in the form of motor deficits, sensory changes, and body representations distortions, and for Complex Regional Pain Syndrome (CRPS), fibromyalgia, and low back pain. Many sensorimotor changes are related to cortical processing, pain, and other clinical characteristics. However, there is very limited evidence that changes in sensorimotor processing actually lead to pain. We therefore propose that the theory is more appropriate for understanding why pain persists rather than how it arises.

Factors Associated with Pain Intensity and Walking Disability After Lumbar Fusion: A Longitudinal Study

STUDY DESIGN

Retrospective longitudinal study.

OBJECTIVE

To identify the preoperative factors associated with postoperative lumbar fusion recovery in back or leg pain, self-reported walking time, and gait speed over a 6-month period.

SUMMARY OF BACKGROUND DATA

The demand for lumbar fusion surgeries has significantly increased over the years. Yet, some patients report persistent postsurgical pain and poor functional outcomes. Unfortunately, the associated risk factors are not well understood.

METHODS

The study analyzed 232 subjects with mono- or bisegmental lumbar fusion surgery who underwent standardized assessment preoperatively and at 4, 12, and 24weeks postoperatively. Preoperative variables collected were demographic, clinical, and psychological variables. Back or leg pain was measured by the Numeric Pain Rating Scale. Walking disability was measured by self-reported walking time and performance-based fast gait speed. Risk factors of pain and walking disability over time were identified using ordinal and linear mixed-effects modeling.

RESULTS

At 6 months post-surgery, 17% of patients reported having moderate or severe back/leg pain and 24% were unable to walk longer than 30 minutes. Greater preoperative self-reported leg weakness frequency and body-mass-index (BMI) were strongly associated with greater pain and walking disability. Additionally, greater preoperative depression symptoms were associated with greater back/leg pain (adjusted odds ratio = 4.0) and shorter walking time (adjusted odds ratio = 2.7)-but not with slower gait speed (difference = 0.01 m/s). Old age and female gender were strongly associated with gait speed but not with self-reported walking time.

CONCLUSION

A sizable proportion of patients had poor pain and walking outcomes even at 6 months post-surgery. Preoperative leg weakness and BMI were consistent risk factors and patients with greater depression symptoms may have poorer self-reported outcomes. Although requiring validation, our study has identified potentially modifiable risk factors which may give clinicians an opportunity to provide early (preoperative) and targeted intervention strategies to optimize postoperative outcomes.

Level of Evidence: NA.

Sensorimotor effects of plasticity-inducing percutaneous peripheral nerve stimulation protocols

BACKGROUND

Electrical stimulation of skin afferents can induce somatosensory plasticity in humans. Nevertheless, it is unknown if this is possible to do through percutaneous stimulation of a peripheral nerve, which will allow for regional anaesthesia interventions. Furthermore, potentiation protocols applied over mainly non-nociceptive fibers inhibit nociception in rodents, but this has not been tested in humans.

OBJECTIVE

to determine whether a protocol aiming to depress the nociceptive circuit and another aiming to potentiate non-nociceptive circuits produce regional hypoalgesia and changes in motor function, applied through percutaneous peripheral nerve stimulation (pPNS), and to assess which of them is more promising for pain relief, immediately and 24 hours after intervention.

METHODS

PT-cLF protocol aims to depress the nociceptive pathway through Pain Threshold, continuous Low Frequency stimulation and ST-bHF aims to produce potentiation of the non-nociceptive pathway, through Sensory Threshold burst stimulation at High Frequency. All subjects (n=29) went through both protocols and a control condition in a randomized and blinded crossover design.

RESULTS

Compared to control, ST-bHF induced distal hypoalgesia, towards electrical (p=0.04) and mechanical stimuli (p=0.02) and produced mechanical hypoesthesia (p=0.02). Contrarily, hypoalgesia was not observed after PT-cLF (p>0.05) but increased electrical motor threshold (p=0.04), reduced motor recruitment (p=0.03), and the subjects reported feeling reduced strength (p<0.01).

CONCLUSION

This works provides evidence that is possible to induce antinociceptive plasticity in a wide territory using pPNS. Moreover, it demonstrates for the first time in humans that a protocol aiming to produce long-term potentiation applied predominantly over non-nociceptive afferents induces hypoesthesia and hypoalgesia.

Disentangling 'sciatica' to understand and characterise somatosensory profiles and potential pain mechanisms

OBJECTIVES

The study aimed to investigate if patients with lumbar radicular pain only and those with combined lumbar radicular pain + radiculopathy differ in their somatosensory profiles and pain experiences.

METHODS

Quantitative sensory testing (QST) was performed in 26 patients (mean age 47 ± 10 years, 10 females) with unilateral leg pain in the L5 or S1 distribution in their main pain area (MPA) and contralateral mirror side, in the relevant foot dermatome on the symptomatic side and in the hand dorsum. Pain experience was captured on the painDETECT.

RESULTS

Eight patients presented with lumbar radicular pain only and 18 patients with combined radicular pain + radiculopathy. Patients with radicular pain only demonstrated widespread loss of function (mechanical detection) bilaterally in the MPA (p<0.003) and hand (p=0.002), increased heat sensitivity in both legs (p<0.019) and cold/heat sensitivity in the hand (p<0.024). QST measurements in the dermatome did not differ compared to HCs and patients with radiculopathy. Patients with lumbar radiculopathy were characterised by a localised loss of function in the symptomatic leg in the MPA (warm, mechanical, vibration detection, mechanical pain threshold, mechanical pain sensitivity p<0.031) and dermatome (mechanical, vibration detection p<0.001), consistent with a nerve root lesion. Pain descriptors did not differ between the two groups with the exception of numbness (p<0.001). Patients with radicular pain did not report symptoms of numbness, while 78% of patients with radiculopathy did.

CONCLUSIONS

Distinct differences in somatosensory profiles and pain experiences were demonstrated for each patient group, suggesting differing underlying pain mechanisms.

Temporal changes in pain processing after whiplash injury, based on Quantitative Sensory Testing: A systematic review

BACKGROUND AND OBJECTIVE

After whiplash injury, some patients develop chronic whiplash-associated disorders. The exact pathophysiology of this chronification is still unclear and more knowledge is needed regarding the different post-injury phases. Therefore, studies were searched that examined temporal changes in pain processing, measured by Quantitative Sensory Testing (QST).

DATABASES AND DATA TREATMENT

This systematic review searched three electronic databases (Medline, Web of Science and Embase) for articles meeting the eligibility requirements. Risk of bias was assessed according to a modified Newcastle-Ottawa Scale.

RESULTS

The 12 included studies presented moderate to good methodological quality. These studies showed altered pain processing within the first month after injury and normalization within 3 months in 59%-78% of the patients. After 3 months, recovery stagnates during the following years. Thermal and widespread mechanical hyperalgesia occur already in the acute phase, but only in eventually non-recovered patients.

CONCLUSIONS

Differences in pain processing between recovering and non-recovering patients can be observed already in the acute phase. Early screening for signs of altered pain processing can identify patients with high risk for chronification. These insights in temporal changes show the importance of rehabilitation in the acute phase. Future research should target to develop a standardized (bed-site) QST protocol and collect normative data which could, in relation with self-reported pain parameters, allow clinicians to identify the risk for chronification.

SIGNIFICANCE

Altered pain processing is present soon after whiplash injury, but usually recovers within 3 months. Non-recovering patients show little to no improvements in the following years. Differences between recovering and non-recovering patients can be observed by Quantitative Sensory Testing already in the acute phase. Therefore, it is considered a feasible and effective tool that can contribute to the identification of high-risk patients and the prevention of chronification.

Contralateral Sensory and Pain Perception Changes in Patients With Unilateral Neuropathy

OBJECTIVE

To test whether contralateral sensory abnormalities in the clinically unaffected area of patients with unilateral neuropathic pain are due to the neuropathy or pain mechanisms.

METHODS

We analyzed the contralateral clinically unaffected side of patients with unilateral painful or painless neuropathy (peripheral nerve injury [PNI], postherpetic neuropathy [PHN], radiculopathy) by standardized quantitative sensory testing following a validated protocol. Primary outcome was the independent contribution of the following variables on the contralateral sensory function using generalized linear regression models: pain intensity, disease duration, etiology, body area, and sensory patterns in the most painful area.

RESULTS

Among 424 patients (PNI n = 256, PHN n = 78, radiculopathy n = 90), contralateral sensory abnormalities were frequent in both painful (n = 383) and painless (n = 41) unilateral neuropathy, demonstrating sensory loss for thermal and mechanical nonpainful stimuli and both sensory loss and gain for painful test stimuli. Analysis by etiology revealed contralateral pinprick hyperalgesia in PHN and PNI. Analysis by ipsilateral sensory phenotype demonstrated mirror-image pinprick hyperalgesia in both mechanical and thermal hyperalgesia phenotypes. Pain intensity, etiology, and affected body region predicted changes in only single contralateral somatosensory parameters. Disease duration had no impact on the contralateral sensory function.

CONCLUSION

Mechanisms of sensory loss seem to spread to the contralateral side in both painful and painless neuropathies. Contralateral spread of pinprick hyperalgesia was restricted to the 2 ipsilateral phenotypes that suggest sensitization; this suggest a contribution of descending net facilitation from supraspinal areas, which was reported in rodent models of neuropathic pain but not yet in human patients.

Pain matters for central sensitization: sensory and psychological parameters in patients with fibromyalgia syndrome

Sensory abnormalities through quantitative sensory testing in fibromyalgia were not substantially influenced by psychological comorbidities. A significant subgroup showed signs of central sensitization, influenced by pain intensity.

Introduction:

Patients suffering from fibromyalgia syndrome (FMS) are heterogenous. They often present with sensory abnormalities and comorbidities.

Objectives:

We aimed to answer the following questions: (1) Is there a specific somatosensory profile in our patient cohort? (2) Can we detect subgroups characterized by a specific combination of sensory and psychological features? and (3) Do psychological parameters influence sensory signs?

Methods:

In 87 patients with FMS quantitative sensory testing was performed on the hand and evaluated in combination with questionnaire results regarding pain, psychological comorbidities, sleep, and functionality.

Results:

Patients presented different somatosensory patterns, but no specific subgroups regarding sensory signs and psychological features were detected. Hypersensitivity for noxious mechanical and thermal stimuli and hyposensitivity for nonnoxious mechanical stimuli were the most prominent features. Thirty-one percent of patients showed signs of central sensitization as indicated by abnormally increased pinprick hyperalgesia or dynamic mechanical allodynia. Central sensitization was associated with higher pain intensities (P < 0.001). Only a small influence of psychiatric comorbidities on mechanical pain sensitivity (P = 0.044) and vibration detection (P = 0.028) was found, which was partly associated with high pain intensities. A small subgroup of patients (11.4%) demonstrated thermal hyposensitivity (loss of small-fiber function).

Conclusion:

Patients with FMS showed various somatosensory abnormalities. These were not significantly influenced by psychological comorbidities. Signs for central sensitization were detected in about one-third of patients and associated with higher pain intensities. This supports the notion of central sensitization being a major pathophysiological mechanism in FMS, whereas small-fiber loss may be less important.

Swallowing impairment in older adults: association with sensorimotor peripheral nerve function from the Health, Aging and Body Composition study

BACKGROUND

The purpose of this study was to examine whether impairments in sensorimotor peripheral nerve function are associated with a higher likelihood of swallowing impairment in older adults.

METHODS

Health, Aging and Body Composition participants (n = 607, age = 75.8 ± 2.7 years, 55.8% women, 32.3% black) underwent peripheral nerve testing at Year 4 and 11 with swallowing difficulty assessed at Year 4 and 15. Nerve conduction amplitude and velocity were measured at the peroneal motor nerve. Sensory nerve function was assessed with the vibration detection threshold and monofilament (1.4-g/10-g) testing at the big toe. Symptoms of lower extremity peripheral neuropathy and difficulty swallowing were collected by self-report. Data analysis was performed using a hierarchical approach. Odds ratios (ORs) were estimated using non-conditional logistic regression.

RESULTS

At Year 15 108 (17.8%) participants had swallowing impairments. In fully adjusted models, the peripheral nerve impairments associated with swallowing impairment were numbness (OR 4.67; 95%CI 2.24-9.75) and poor motor nerve conduction velocity (OR 2.26; 95%CI 1.08-4.70). Other peripheral nerve impairments were not related to swallowing.

CONCLUSIONS

The association between slow motor nerve conduction velocity and numbness and a higher likelihood of swallowing difficulties a decade later in our prospective study identifies an important area for further investigation in older adults.

Somatosensory profiles in patients with non-specific neck-arm pain with and without positive neurodynamic tests

Despite normal neurological integrity tests, some patients with non-specific neck-arm pain (NSNAP) have heightened nerve mechanosensitivity upon neurodynamic testing. The aim of this study was to determine whether or not a nerve dysfunction is present in patients with positive neurodynamic tests compared to those with negative neurodynamic tests or healthy controls. Somatosensory profiling using quantitative sensory testing (QST) was established in 40 consecutive patients with unilateral NSNAP; 23 had positive upper limb neurodynamic tests (ULNT_POS) and 17 had negative neurodynamic tests (ULNT_NEG) and in 26 healthy controls. QST included measurement of thermal and mechanical detection and pain thresholds in the maximal pain area on the symptomatic side as well as the corresponding contralateral area. Fifty-seven percent of patients with NSNAP had positive neurodynamic tests. Somatosensory profiling revealed a loss of function phenotype in NSNAP patients compared to healthy controls both in the maximal pain area and asymptomatic side. Hyperalgesia (cold, heat and pressure) was present bilaterally in both NSNAP groups. Direct comparison between the patient groups revealed no significant differences in somatosensory profiles. However, the ULNT_POS group demonstrated sensory loss compared to healthy controls in more parameters than the ULNT_NEG group. The ULNT_NEG subgroup represented an intermediate phenotype between ULNT_POS patients and healthy controls in most detection thresholds as well as thermal and pressure pain thresholds. Even though patients with NSNAP present as a spectrum, it remains unclear whether the sensory changes are indicative of a nerve dysfunction/lesion or rather a marker of altered central pain processing.

Advances in diagnosis, classification, pathophysiology, and management of trigeminal neuralgia

Trigeminal neuralgia is a very painful neurological condition with severe, stimulus-evoked, short-lasting stabbing pain attacks in the face. The past decade has offered new insights into trigeminal neuralgia symptomatology, pathophysiology, and treatment, leading to a change in the classification of the condition. An accurate diagnosis is crucial because neuroimaging interpretation and clinical management differ among the various forms of facial pain. MRI using specific sequences should be a part of the diagnostic workup to detect a possible neurovascular contact and exclude secondary causes. Demonstration of a neurovascular contact should not be used to confirm a diagnosis but rather to facilitate surgical decision making. Carbamazepine and oxcarbazepine are drugs of first choice for long-term treatment, whereas microvascular decompression is the first-line surgery in medically refractory patients. Advances in neuroimaging techniques and animal models will provide further insight into the causes of trigeminal neuralgia and its pathophysiology. Development of more efficacious treatment options is highly warranted.

Aberrant pain modulation in trigeminal neuralgia patients

Objectives The present study attempts to understand the role of supraspinal nociceptive pain modulation in typical trigeminal neuralgia (TN) patients by using a conditioned pain modulation paradigm and estimation of plasma levels of two important neuromodulators; Calcitonin Gene-Related Peptide and β-endorphin. Methods Twenty TN patients and 20 healthy, age and gender-matched subjects participated in the study. The participants' hot pain thresholds (HPT) were measured over their affected side on the face. Testing sites were matched for healthy controls. For the conditioned pain modulation their contralateral foot was immersed in noxious cold (5 °C) water bath (conditioning stimuli) for 30 s and HPT (testing stimuli) was determined before, during and till 5 min after the immersion. Plasma Calcitonin Gene-Related Peptide and β-endorphin levels were estimated to understand their role in disease pathogenesis and pain modulation. Results Change in HPT during foot immersion was significantly higher in healthy controls compared to TN patients (p<0.0001). The changes recorded in HPT in patients, were significant only in 2nd and 3rd minute post immersion. While in healthy controls, the effect lasted till the 4th minute. The concentration of beta-endorphin was significantly lower in TN patients (p=0.003) when compared to healthy controls. Conclusions The results suggest that there is an impairment in supraspinal pain modulation also known as Diffuse Noxious Inhibitory Controls in typical TN and that the reduced levels of β-endorphin may contribute to the chronic pain state experienced by patients.

Association of quantitative sensory testing parameters with clinical outcome in patients with lumbar radiculopathy undergoing microdiscectomy

Background/Aim

This study aimed to establish the somatosensory profile of patients with lumbar radiculopathy at pre‐and post‐microdiscectomy and to explore any association between pre‐surgical quantitative sensory test (QST) parameters and post‐surgical clinical outcomes.

Methods

A standardized QST protocol was performed in 53 patients (mean age 38 ± 11 years, 26 females) with unilateral L5/S1 radiculopathy in the main pain area (MPA), affected dermatome and contralateral mirror sites and in age‐ and gender‐,and body site‐matched healthy controls. Repeat measures at 3 months included QST, the Oswestry Disability Index (ODI) and numerous other clinical measures; at 12 months, only clinical measures were repeated. A change <30% on the ODI was defined as ‘no clinically meaningful improvement’.

Results

Patients showed a significant loss of function in their symptomatic leg both in the dermatome (thermal, mechanical, vibration detection p < .002), and MPA (thermal, mechanical, vibration detection, mechanical pain threshold, mechanical pain sensitivity p < .041) and increased cold sensitivity in the MPA (p < .001). Pre‐surgical altered QST parameters improved significantly post‐surgery in the dermatome (p < .018) in the symptomatic leg and in the MPA (p < .010), except for thermal detection thresholds and cold sensitivity. Clinical outcomes improved at 3 and 12 months (p < .001). Seven patients demonstrated <30% change on the ODI at 12 months. Baseline loss of function in mechanical detection in the MPA was associated with <30% change on the ODI at 12 months (OR 2.63, 95% CI 1.09–6.37, p = .032).

Conclusion

Microdiscectomy resulted in improvements in affected somatosensory parameters and clinical outcomes. Pre‐surgical mechanical detection thresholds may be predictive of clinical outcome.

Significance

This study documented quantitative sensory testing (QST) profiles in patients with lumbar radiculopathy in their main pain area (MPA) and dermatome pre‐ and post‐microdiscectomy and explored associations between QST parameters and clinical outcome. Lumbar radiculopathy was associated with loss of function in modalities mediated by large and small sensory fibres. Microdiscectomy resulted in significant improvements in loss of function and clinical outcomes in 85% of our cohort. Pre‐surgical mechanical detection thresholds in the MPA may be predictive of clinical outcome.

Interobserver agreement of an electronic von Frey device for measuring mechanical sensory thresholds in normal dogs

Electronic von Frey Aesthesiometry (VFA) has been previously reported as a useful method of mechanical quantitative sensory testing (QST) for evaluating neuropathic pain in dogs. Intraobserver agreement has been shown to be good to excellent; however, interobserver agreement has not been evaluated and is vital to the use of this technique in multicenter veterinary clinical trials in neuropathic pain. The goal of this study was to evaluate the interobserver agreement of sensory thresholds obtained using electronic VFA in a group of normal small breed dogs. Twenty healthy dogs (<20 kg) were recruited from the general practice population at the Ohio State University Veterinary Medical Center. Three clinically experienced yet QST novice evaluators used an electronic von Frey device to measure mechanical sensory threshold (ST) after a standardised training session conducted by an expert evaluator. Each dog was assessed by all three evaluators on the same day with both evaluator and limb test order randomised and testing sessions separated by 5 min. Mean ST values were averaged for all four limbs to produce a single value per dog for comparison between evaluators. Agreement between evaluators was determined using the intra-class correlation coefficient (ICC; two-way model for consistency, single measures). ICC across all three evaluators was 0.48, indicating moderate agreement. Moderate interobserver agreement is not sufficient to support the use of this technique in multi-center clinical trials, and our results underscore the importance of using a single evaluator for this QST technique until better agreement can be demonstrated.

Reversible tactile hypoesthesia associated with myofascial trigger points: a pilot study on prevalence and clinical implications

Introduction:

Tactile hypoesthesia observed in patients with myofascial pain syndrome (MPS) is sometimes reversible when pain is relieved by trigger point injections (TPIs). We aimed to investigate the prevalence of such reversible hypoesthesia during TPI therapy and topographical relations between areas of tactile hypoesthesia and myofascial trigger points (MTrP) in patients with MPS.

Methods:

Forty-six consecutive patients with MTrP were enrolled in this study. We closely observed changes in areas of tactile hypoesthesia in patients who had tactile hypoesthesia at the first visit, and throughout TPI therapy. Tactile stimulation was given using cotton swabs, and the areas of tactile hypoesthesia were delineated with an aqueous marker and recorded in photographs.

Results:

A reduction in the size of hypoesthetic area with TPI was observed in 27 (58.7%) patients. All the 27 patients experienced a reduction in pain intensity by more than 50% in a numerical rating scale score through TPI therapy. In 9 patients, the reduction in the sizes of hypoesthetic areas occurred 10 minutes after TPI. Complete disappearance of tactile hypoesthesia after TPI therapy was observed in 6 of the 27 patients. Myofascial trigger points were located in the muscles in the vicinity of ipsilateral cutaneous dermatomes to which the hypoesthetic areas belonged.

Conclusion:

Our results indicate a relatively high prevalence of reversible tactile hypoesthesia in patients with MPS. Mapping of tactile hypoesthetic areas seems clinically useful for detecting MTrP. In addition, treating MTrP with TPI may be important for distinguishing tactile hypoesthesia associated with MPS from that with neuropathic pain.

High Temporal Summation of Pain Predicts Immediate Analgesic Effect of Acupuncture in Chronic Pain Patients-A Prospective Cohort Study

Objectives: This prospective cohort study explored whether two distinguished sensory parameters predicted acupuncture effects in chronic pain patients; namely high temporal summation of pain (TS) indicating spinal synaptic facilitation as well as a low vibration detection threshold (VDT) indicating a loss of Aβ-fiber function. Methods: Pinprick induced TS and VDT were assessed by standardized, validated methods at the most painful body site and a pain free control site in 100 chronic pain patients receiving six acupuncture sessions as part of an interdisciplinary multimodal pain treatment (IMPT). Immediate change in pain intensity after the first acupuncture session (first treatment on the first day of IMPT) was assessed by the verbal rating scale (VRS, 0-100). After 4 weeks of treatment, patients indicated in a questionnaire whether acupuncture had relieved pain immediately and whether it had contributed to overall pain reduction and well-being after IMPT. Results: Logistic regression analysis revealed an association between high TS at the control site and a reduction in pain intensity of at least 30% (VRS) after the first acupuncture (OR [95%-CI] 4.3 [1.6-11.8]). Questionnaire ratings of immediate pain relief after acupuncture were associated with high TS at the control site (OR [95%-CI] 3.8 [1.4-10.2] any pain relief, OR [95%-CI] 5.5 [1.7-17.1] over 50% pain reduction) and at the pain site (OR [95%-CI] 3.2 [1.2-8.9] any pain relief). Appraisals of the contribution of acupuncture to overall pain reduction and well-being after IMPT were not associated with TS. The VDT was not associated with any outcome. Conclusion: This explorative study provides first-time evidence that high TS, especially at a pain free control site, but not VDT, might predict immediate analgesic response to acupuncture in chronic pain patients. Thus, highly centrally sensitized chronic pain patients might respond particularly well to acupuncture.

Chronic Central Pain Among Community-Dwelling Survivors of Moderate-to-Severe Traumatic Brain Injury: A Quantitative Sensory Testing Study

Background:

Central pain associated with changes in sensory thresholds is one of the most enduring consequences of major trauma. Yet it remains sparsely studied among community-dwelling survivors of moderate-to-severe traumatic brain injury (TBI).

Purpose:

To describe and compare thermal and mechanical sensory thresholds in home-based patients with and without central pain after moderate-to-severe TBI with a cohort of healthy controls.

Design:

Cross-sectional.

Method:

Thresholds for cold/heat detection, thermal pain, touch, and distorted sensation were gathered using quantitative sensory testing (QST). QST was performed on the painful and contralateral pain-free body regions in TBI participants with pain (TBI-P) and on both forearms in TBI participants without pain (TBI-NP) and healthy controls (HC). Central pain was characterized using the Brief Pain Inventory–Short Form.

Results:

We tested 16 TBI-P patients, 17 TBI-NP patients, and 16 HC. Mean time since injury for TBI patients was 24 ± 15 months. TBI-P and TBI-NP patients showed significant loss in innocuous mechanical sensitivity compared to HC ( F = 18.929; Bonferroni-adjusted p ≤ .001). Right–left differences in cold pain sensations were significantly larger in TBI-P than in TBI-NP and HC participants ( F = 14.352; Bonferroni-adjusted p ≤ .001). Elevated heat sensitivity thresholds were also observed in TBI-P participants but remained within normal range.

Conclusion:

Damage to cutaneous mechanoreceptors is a necessary, but not sufficient, condition for the development of chronic central pain following TBI. Damage or incomplete recovery of cutaneous thermoreceptors may be a contributing factor to chronic pain after TBI.

Dynamic of the somatosensory system in postherpetic neuralgia

Introduction:

In postherpetic neuralgia (PHN) different types of patients can be distinguished regarding their predominant peripheral nociceptor function.

Objective:

The aim was to examine somatosensory profiles in the course of disease with special regard to the different subtypes existing in PHN.

Methods:

Twenty patients with PHN (7 men and 13 women, age 67 ± 9.6 years) were examined at baseline (disease duration 18.1 ± 26 months) and follow-up (31.6 ± 23.8 months later) with quantitative sensory testing (protocol of the German Research Network on Neuropathic Pain).

Results:

Fourteen (70%) PHN patients presented with impaired (iPHN) and 6 (30%) with preserved (pPHN) C-fiber function. Groups did not differ regarding age, disease duration, or pain intensity at baseline. Both groups did not differ regarding change in pain intensity (−0.5 ± 2.3 vs −1.7 ± 2.6 numerical rating scale, P = n.s.) at follow-up. Impaired PHN improved in thermal and mechanical detection thresholds as well as allodynia independent from change in pain intensity. By contrast, pPHN showed an increase in mechanical pain sensitivity (1.4 ± 2.5 vs −0.4 ± 2.2, P < 0.05) and a trend towards a stronger loss of detection (66% vs 33%, P = n.s.) on follow-up.

Conclusion:

Results demonstrate that patients with preserved C-fiber function are more predisposed to develop signs of central sensitization as demonstrated by an increased mechanical pain sensitivity. Impaired C-fiber function is able to improve even in chronic cases, but a functional loss is unlikely to play a role here. The knowledge of development of somatosensory profiles in the course of the disease offers possibilities to optimize a mechanism-based treatment.

Multicenter assessment of quantitative sensory testing (QST) for the detection of neuropathic-like pain responses using the topical capsaicin model

Background

The use of quantitative sensory testing (QST) in multicenter studies has been quite limited, due in part to lack of standardized procedures among centers.

Aim

The aim of this study was to assess the application of the capsaicin pain model as a surrogate experimental human model of neuropathic pain in different centers and verify the variation in reports of QST measures across centers.

Methods

A multicenter study conducted by the Quebec Pain Research Network in six laboratories allowed the evaluation of nine QST parameters in 60 healthy subjects treated with topical capsaicin to model unilateral pain and allodynia. The same measurements (without capsaicin) were taken in 20 patients with chronic neuropathic pain recruited from an independent pain clinic.

Results

Results revealed that six parameters detected a significant difference between the capsaicin-treated and the control skin areas: (1) cold detection threshold (CDT) and (2) cold pain threshold (CPT) are lower on the capsaicin-treated side, indicating a decreased in cold sensitivity; (3) heat pain threshold (HPT) was lower on the capsaicin-treated side in healthy subjects, suggesting an increased heat pain sensitivity; (4) dynamic mechanical allodynia (DMA); (5) mechanical pain after two stimulations (MPS2); and (6) mechanical pain summation after ten stimulations (MPS10), are increased on the capsaicin-treated side, suggesting an increased in mechanical pain (P < 0.002). CDT, CPT and HPT showed comparable effects across all six centers, with CPT and HPT demonstrating the best sensitivity. Data from the patients showed significant difference between affected and unaffected body side but only with CDT.

Conclusion

These results provide further support for the application of QST in multicenter studies examining normal and pathological pain responses.

Sensory modulation dysfunction is associated with Complex Regional Pain Syndrome

OBJECTIVE

Complex Regional Pain Syndrome (CRPS), a chronic pain condition, develops mainly after limb trauma and severely inhibits function. While early diagnosis is essential, factors for CRPS onset are elusive. Therefore, identifying those at risk is crucial. Sensory modulation dysfunction (SMD), affects the capacity to regulate responses to sensory input in a graded and adaptive manner and was found associated with hyperalgesia in otherwise healthy individuals, suggestive of altered pain processing.

AIM

To test SMD as a potential risk factor for CRPS.

METHODS

In this cross-sectional study, forty-four individuals with CRPS (29.9±11 years, 27 men) and 204 healthy controls (27.4±3.7 years, 105 men) completed the Sensory Responsiveness Questionnaire-Intensity Scale (SRQ-IS). A physician conducted the CRPS Severity Score (CSS), testing individuals with CRPS.

RESULTS

Thirty-four percent of the individuals with CRPS and twelve percent of the healthy individuals were identified to have SMD (χ2 (1) = 11.95; p<0.001). Logistic regression modeling revealed that the risk of CRPS is 2.68 and 8.21 times higher in individuals with sensory over- and sensory under-responsiveness, respectively, compared to non-SMD individuals (p = 0.03 and p = 0.01, respectively).

CONCLUSIONS

SMD, particularly sensory under-responsiveness, might serve as a potential risk factor for CRPS and therefore screening for SMD is recommended. This study provides the risk index probability clinical tool a simple evaluation to be applied by clinicians in order to identify those at risk for CRPS immediately after injury. Further research is needed.

Sensory Function and Chronic Pain in Multiple Sclerosis

Objective

To examine whether hypoesthesia and chronic pain are related in patients with MS.

Methods

Sixty-seven MS patients with pain and 80 persons without MS were included. Sensory functioning was tested by bedside neurological examination. Touch, joint position (dorsal column-medial lemniscus pathway), temperature sense, and pain (spinothalamic tract) were tested. Pain intensity was measured by the Colored Analogue Scale (CAS Intensity) and the Faces Pain Scale (FPS); pain affect was also measured by CAS Affect and Number of Words Chosen-Affective (NWC-A). Mood was assessed with the SCL-90 anxiety and depression subscales and the Beck Depression Inventory (BDI).

Results

A significant negative relationship was found between pain intensity and the function of the dorsal column-medial lemniscal pathway, but not with the spinothalamic tract.

Conclusion

In addition to the already known relation between hyperesthesia and pain, hypoesthesia for touch and joint position also seems to be related to chronic pain in MS patients.

Quantitative sensory testing after macroreplantation: evidence for a specific somatosensory profile

A comprehensive functional recovery is one of the criteria for successful replantation of an amputated limb. Functionality of a replanted limb is strongly dependent on its regained sensibility. In previous studies concerning the sensibility of replanted limbs, only a few somatosensory submodalities were examined in small samples. The purpose of this study is to provide a full pattern of somatosensory symptoms after replantation. Quantitative sensory testing was performed according to a standardized protocol in a sample of 15 patients who underwent replantation of their upper limb proximal to the radiocarpal joint (macroreplantation). Results indicate that most of these patients showed a specific somatosensory profile characterized by thermal and mechanical hypoesthesia and hyperalgesia in response to pressure pain, whereas no single case of hyperalgesia to heat pain occurred. This distinct profile of impaired somatosensation shares some features of the somatosensory profile of neuropathic pain syndromes. Patients' limbs that were replanted many years before the present quantitative sensory testing showed more sensory deficits than patients with more recent replantations. This knowledge might be helpful in the development of more specific and more successful rehabilitation programs with replanted patients and improves the behavioral function of the replanted limb.

Somatosensory Test Responses and Physical and Psychological Functioning of Children and Adolescents with Chronic Non-neuropathic Pain: An Exploratory Study

OBJECTIVES

This study was designed to establish preliminary feasibility testing of a set of inherently benign somatosensory stimulus-response tests (to cutaneous and deep stimuli) for bedside or office evaluation of pain disorders in children and adolescents. Associations between, and the relative influence of, cutaneous somatosensory testing (SST) responses, deep SST responses, and psychological factors (depression, pain-related catastrophizing) on pain outcomes (worst pain intensity, pain-related disability) were considered.

METHODS

Sixty participants (6 to 18 y) were recruited from the pediatric chronic pain clinic. SST responses were assessed at the pain site (PS) and control sites to diverse stimuli (static/dynamic touch, punctate pressure, vibration, cool, deep pressure) using Colored Analogue Scales (CAS) with modified anchors. Validated measures of depression, pain-related catastrophizing, and pain-related functional interference were administered.

RESULTS

Responses at the PS were more frequently hypersensitive than hyposensitive for all SST measures except vibration. Deep pressure responses were the only statistically significant predictor of worst pain intensity. Depression and pain-related catastrophizing accounted for a statistically significant amount of variance of pain-related disability, over and above that which was accounted for by SST responses.

DISCUSSION

Preliminary feasibility of a set of somatosensory stimulus-response tests for bedside or office evaluation of pain disorders in children and adolescents was established. Deep pressure responses contributed unique information in predicting worst pain intensity but not functional interference. Although cutaneous SST responses at the PSs were frequently abnormal, cutaneous SST responses were not confirmed in this study to have clinical utility, but rather might be centrally mediated epiphenomena.

Somatosensory and Biomechanical Abnormalities in Females With Patellofemoral Pain

OBJECTIVES

Chronic patellofemoral pain (PFP) is a common orthopedic condition for which little is understood of the alterations in pain processing such as hyperalgesia, hypoesthesia, and the relationship of altered knee mechanics to hyperalgesia. We assessed pain, pressure pain thresholds (PPT), detection to light touch, and the relationship of pain and PPTs to knee abduction angle during a stair step down task between females with and without PFP.

MATERIALS AND METHODS

Twenty females diagnosed with PFP and 20 age-matched pain-free females participated in this study. Individuals underwent an instrumented assessment of knee mechanics during a stair step down task, PPT and detection of light touch over the center of the patella and lateral retinaculum, and PPT outside painful area over the right elbow.

RESULTS

The PFP group had significantly lower PPT values at the patella (P=0.02), lateral retinaculum (P=0.001), and at the elbow (P=0.03). There was an elevated threshold to detect light touch over the center of their patella (P=0.04). A significant relationship between both pain (r=-0.49, P=0.03) and PPT values (r=0.65, P=0.004) to the frontal plane knee angle existed in the PFP group which was not present in the control group (r=-0.17, P=0.49) or in the elbow (r=-0.009, P=0.972).

DISCUSSION

These results suggest that PFP is characterized by an increase in both localized and centralized pain sensitivity that is related to movement mechanics. Thus, PFP has both biomechanical, nociceptive components as well as inferred aspects of altered central sensitization.

A standardized clinical evaluation of phenotypic diversity in diabetic polyneuropathy

Diabetic polyneuropathy (DPN) is a major cause of neuropathic pain and a frequent target condition in analgesic treatment trials. Differences in the clinical symptoms and signs associated with DPN suggest distinct pathophysiological mechanisms underlying nerve damage and dysfunction that are likely to have therapeutic relevance. The aim of this study was to develop a tool for the bedside assessment of painful neuropathies such as DPN that captures the diversity of phenotypes. Sixty-one patients with type 2 diabetes and painful neuropathy, 19 patients with painless DPN, 25 patients with type 2 diabetes but no clinical evidence of neuropathy, and 20 healthy control subjects completed a structured interview (47 items) and a standardized physical examination (39 items). After analyzing critical features of pain and painless symptoms and examining the outcome of physical tests of sensory function, we determined principal components of the phenotypic variance among patients. Increased sensitivity to mechanical or thermal stimuli and, to a lesser extent, the sensory quality of pain or paresthesia were the most discriminating elements of DPN phenotypes. Correlation patterns of symptoms and signs indicated the involvement of functionally distinct nerve fiber populations. We combined interview questions and physical tests identifying these differences in a shortened assessment protocol that we named Standardized Evaluation of Pain and Somatosensory Function (StEPS). The protocol StEPS generates a phenotypic profile of patients with neuropathy. Separate intensity ratings for spontaneous painful symptoms and pain evoked by standard stimuli support a detailed documentation of neuropathic pain and its response to analgesic treatment.

Plantar reflex excitability is increased in the evening in restless legs syndrome patients

OBJECTIVE

To investigate if diurnal changes in spinal excitability (plantar reflex) occur in restless legs syndrome (RLS) participants compared to healthy matched controls.

METHODS

Thirteen RLS participants and 13 healthy control participants' plantar reflex responses were evaluated in the evening (PM) and the morning (AM). Plantar reflex responses were assessed electromyographically, using motion analysis (kinematically) and by subjective nociception (Visual Analogue Scale).

RESULTS

RLS participants showed a circadian variation in plantar reflex responses whilst control participants did not. Evening ankle angle changes were larger and faster in RLS participants compared to morning responses. In addition RLS participants displayed significantly smaller change in ankle angle and significantly slower ankle movements in the evening and the morning as well as significantly lower lateral gastrocnemius maximum amplitude in the compared to control participants.

CONCLUSION

The findings of the current study support the theory of RLS circadian fluctuations in spinal excitability. An unexpected finding was decreased plantar reflex responses in RLS participants compared to healthy control participants. However this finding supports the theory of mechanical hypoesthesia in RLS. The results of this study provide further insight into the pathophysiology of RLS, highlighting that not all sensory processing is affected in the same manner.

Nondermatomal somatosensory deficits in chronic pain are associated with cerebral grey matter changes

OBJECTIVES

Widespread sensory deficits occur in 20-40% of chronic pain patients on the side of pain, independent of pain aetiology, and are known as nondermatomal sensory deficits (NDSDs). NDSDs can occur in absence of central or peripheral nervous system lesions. We hypothesised that NDSDs were associated with cerebral grey matter changes in the sensory system and in pain processing regions, detectable with voxel-based morphometry.

METHODS

Twenty-five patients with NDSDs, 23 patients without NDSDs ("pain-only"), and 29 healthy controls were studied with high resolution structural MRI of the brain. A comprehensive clinical and psychiatric evaluation based on Diagnostic and Statistical Manual was performed in all patients.

RESULTS

Patients with NDSDs and "pain-only" did not differ concerning demographic data and psychiatric diagnoses, although anxiety scores (HADS-A) were higher in patients with NDSDs. In patients with NDSDs, grey matter increases were found in the right primary sensory cortex, thalamus, and bilaterally in lateral temporal regions and the hippocampus/fusiform gyrus. "Pain-only" patients showed a bilateral grey matter increase in the posterior insula and less pronounced changes in sensorimotor cortex.

CONCLUSIONS

Dysfunctional sensory processing in patients with NDSDs is associated with complex changes in grey matter volume, involving the somatosensory system and temporal regions.

Ipsilateral and contralateral sensory changes in healthy subjects after experimentally induced concomitant sensitization and hypoesthesia

BACKGROUND

In unilateral neuropathic pain. e.g. after peripheral nerve injury, both positive and negative sensory signs occur often, accompanied by minor but equally directed contralateral sensory changes. To mimic this feature, we experimentally aimed to induce concomitant c-fibre sensitization and block in healthy subjects and analyzed the bilateral sensory changes by quantitative sensory testing (QST) using the protocol of the German Research Network on Neuropathic Pain.

METHODS

Twenty eight healthy subjects were firstly randomized in 2 groups to receive either topical capsaicin (0.6%, 12 cm², application duration: 15 min.) or a lidocaine/prilocaine patch (25/25 mg, 10 cm², application duration: 60 min.) on the right volar forearm. Secondly, 7-14 days later in the same area either at first capsaicin (for 15 min.) and immediately afterwards local anesthetics (for 60 min.) was applied (Cap/LA), or in inversed order with the same application duration (LA/Cap). Before, after each application and 7-14 days later a QST was performed bilaterally.

STATISTICS

Wilcoxon-test, ANOVA, p < 0.05.

RESULTS

Single application of 0,6% capsaicin induced thermal hypoesthesia, cold hypoalgesia, heat hyperalgesia and tactile allodynia. Lidocaine/prilocaine alone induced thermal and tactile hypoesthesia as well as mechanical and cold hypoalgesia, and a heat hyperalgesia (to a smaller extent). Ipsilaterally both co-applications induced a combination of the above mentioned changes. Significant contralateral sensory changes occurred only after the co-application with concomitant sensitization and hypoesthesia and comprised increased cold (Cap/LA, LA/Cap) and mechanical detection as well as cold pain threshold (LA/Cap).

CONCLUSION

The present experimental model using combined application of capsaicin and LA imitates partly the complex sensory changes observed in patients with unilateral neuropathic pain and might be used as an additional surrogate model. Only the concomitant use both agents in the same area induces both positive and negative sensory signs ipsilaterally as well as parallel contralateral sensory changes (to a lesser extent).

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT01540877 , registered on 23 February 2012.

Mechanisms of chronic pain - key considerations for appropriate physical therapy management

In last decades, knowledge of nociceptive pain mechanisms has expanded rapidly. The use of quantitative sensory testing has provided evidence that peripheral and central sensitization mechanisms play a relevant role in localized and widespread chronic pain syndromes. In fact, almost any patient suffering with a chronic pain condition will demonstrate impairments in the central nervous system. In addition, it is accepted that pain is associated with different types of trigger factors including social, physiological, and psychological. This rational has provoked a change in the understanding of potential mechanisms of manual therapies, changing from a biomechanical/medical viewpoint, to a neurophysiological/nociceptive viewpoint. Therefore, interventions for patients with chronic pain should be applied based on current knowledge of nociceptive mechanisms since determining potential drivers of the sensitization process is critical for effective management. The current paper reviews mechanisms of chronic pain from a clinical and neurophysiological point of view and summarizes key messages for clinicians for proper management of individuals with chronic pain.

Neuropathic pain: an updated grading system for research and clinical practice

The redefinition of neuropathic pain as “pain arising as a direct consequence of a lesion or disease affecting the somatosensory system,” which was suggested by the International Association for the Study of Pain (IASP) Special Interest Group on Neuropathic Pain (NeuPSIG) in 2008, has been widely accepted. In contrast, the proposed grading system of possible, probable, and definite neuropathic pain from 2008 has been used to a lesser extent. Here, we report a citation analysis of the original NeuPSIG grading paper of 2008, followed by an analysis of its use by an expert panel and recommendations for an improved grading system. As of February, 2015, 608 eligible articles in Scopus cited the paper, 414 of which cited the neuropathic pain definition. Of 220 clinical studies citing the paper, 56 had used the grading system. The percentage using the grading system increased from 5% in 2009 to 30% in 2014. Obstacles to a wider use of the grading system were identified, including (1) questions about the relative significance of confirmatory tests, (2) the role of screening tools, and (3) uncertainties about what is considered a neuroanatomically plausible pain distribution. Here, we present a revised grading system with an adjusted order, better reflecting clinical practice, improvements in the specifications, and a word of caution that even the “definite” level of neuropathic pain does not always indicate causality. In addition, we add a table illustrating the area of pain and sensory abnormalities in common neuropathic pain conditions and propose areas for further research.

Trigeminal neuralgia - diagnosis and treatment

Introduction Trigeminal neuralgia (TN) is characterized by touch-evoked unilateral brief shock-like paroxysmal pain in one or more divisions of the trigeminal nerve. In addition to the paroxysmal pain, some patients also have continuous pain. TN is divided into classical TN (CTN) and secondary TN (STN). Etiology and pathophysiology Demyelination of primary sensory trigeminal afferents in the root entry zone is the predominant pathophysiological mechanism. Most likely, demyelination paves the way for generation of ectopic impulses and ephaptic crosstalk. In a significant proportion of the patients, the demyelination is caused by a neurovascular conflict with morphological changes such as compression of the trigeminal root. However, there are also other unknown etiological factors, as only half of the CTN patients have morphological changes. STN is caused by multiple sclerosis or a space-occupying lesion affecting the trigeminal nerve. Differential diagnosis and treatment Important differential diagnoses include trigeminal autonomic cephalalgias, posttraumatic or postherpetic pain and other facial pains. First line treatment is prophylactic medication with sodium channel blockers, and second line treatment is neurosurgical intervention. Future perspectives Future studies should focus on genetics, unexplored etiological factors, sensory function, the neurosurgical outcome and complications, combination and neuromodulation treatment as well as development of new drugs with better tolerability.

Bone Trauma Causes Massive but Reversible Changes in Spinal Circuitry

Bone fracture with subsequent immobilization of the injured limb can cause complex regional pain syndrome (CRPS) in humans. Mechanisms of CRPS are still not completely understood but bone fracture with casting in mice leads to a similar post-traumatic inflammation as seen in humans and might therefore be an analog to human CRPS. In this article we report behavioral and spinal electrophysiological changes in mice that developed swelling of the paw, warming of the skin, and pain in the injured limb after bone fracture. The receptive field sizes of spinal neurons representing areas of the hind paws increased after trauma and recovered over time-as did the behavioral signs of inflammation and pain. Interestingly, both sides-the ipsi- and the contralateral limb-showed changes in mechanical sensitivity and neuronal network organization after the trauma. The characteristics of evoked neuronal responses recorded in the dorsal horn of the mice were similar between uninjured controls and fractured animals. However, we saw a caudal extension of the represented area of the hind paw in the spinal cord at the injured side and an occurrence of large receptive fields of wide dynamic range neurons. The findings in mice compare with human symptoms in CRPS with ipsi- and also contralateral allodynia and pain. In all mice tested, all signs subsided 12 weeks after trauma. Our data suggest a significant reorganization of spinal circuitry after limb trauma, in a degree more comprehensive than most models of neuropathies. This process seems to be reversible in the rodent.

PERSPECTIVE

The discovery of enlarged spinal neuronal receptive fields and caudal extension of the representation area of the injured body part, which subsides several weeks after a bone trauma in mice, might give hope to patients of CRPS if-in the future-we are able to translate the rodent recovery mechanisms to post-traumatic humans.

Profound alteration in cutaneous primary afferent activity produced by inflammatory mediators

Inflammatory pain is thought to arise from increased transmission from nociceptors and recruitment of 'silent' afferents. To evaluate inflammation-induced changes, mice expressing GCaMP3 in cutaneous sensory neurons were generated and neuronal responses to mechanical stimulation in vivo before and after subcutaneous infusion of an 'inflammatory soup' (IS) were imaged in an unanesthetized preparation. Infusion of IS rapidly altered mechanical responsiveness in the majority of neurons. Surprisingly, more cells lost, rather than gained, sensitivity and 'silent' afferents that were mechanically insensitive and gained mechanosensitivity after IS exposure were rare. However, the number of formerly 'silent' afferents that became mechanosensitive was increased five fold when the skin was heated briefly prior to infusion of IS. These findings suggest that pain arising from inflamed skin reflects a dramatic shift in the balance of sensory input, where gains and losses in neuronal populations results in novel output that is ultimately interpreted by the CNS as pain.

Persistent idiopathic facial pain – a prospective systematic study of clinical characteristics and neuroanatomical findings at 3.0 Tesla MRI

Introduction

Persistent idiopathic facial pain (PIFP) is a poorly understood chronic orofacial pain disorder and a differential diagnosis to trigeminal neuralgia. To address the lack of systematic studies in PIFP we here report clinical characteristics and neuroimaging findings in PIFP.

Methods

Data collection was prospective and standardized in consecutive PIFP patients. All patients underwent 3.0 MRI.

Results

In a cohort of 53 PIFP patients, the average age of onset was 44.1 years. PIFP was found in more women 40 (75%) than men 13 (25%), p < 0.001. There was a high prevalence of bilateral pain 7 (13%), hypoesthesia 23 (48%), depression 16 (30%) and other chronic pain conditions 17 (32%) and a low prevalence of stabbing pain 21 (40%), touch-evoked pain 14 (26%) and remission periods 10 (19%). The odds ratio between neurovascular contact and the painful side was 1.4 (95% Cl 0.4–4.4, p = 0.565) and the odds ratio between neurovascular contact with displacement of the trigeminal nerve and the painful side was 0.2 (95% Cl 0.0–2.1, p = 0.195).

Conclusion

PIFP is separated from trigeminal neuralgia both with respect to the clinical characteristics and neuroimaging findings, as NVC was not associated to PIFP.

Complex regional pain syndrome-significant progress in understanding

Research into complex regional pain syndrome (CRPS) has made significant progress. First, there was the implementation of the official IASP "Budapest" diagnostic criteria. It would be desirable to also define exclusion and outcome criteria that should be reported in studies. The next step was to recognize the complex pathophysiology. After trauma, some inflammation is physiological; in acute CRPS, this inflammation persists for months. There is an abundance of inflammatory and a lack of anti-inflammatory mediators. This proinflammatory network (cytokines and probably also other mediators) sensitizes the peripheral and spinal nociceptive system, it facilitates the release of neuropeptides from nociceptors inducing the visible signs of inflammation, and it stimulates bone cell or fibroblast proliferation, and endothelial dysfunction leading to vascular changes. Trauma may also expose nervous system structures to the immune system and triggers autoantibodies binding to adreno- and acetylcholine receptors. In an individual time frame, the pain in this inflammatory phase pushes the transition into "centralized" CRPS, which is dominated by neuronal plasticity and reorganization. Sensory-motor integration becomes disturbed, leading to a loss of motor function; the body representation is distorted leading to numbness and autonomic disturbances. In an attempt to avoid pain, patients neglect their limb and learn maladaptive nonuse. The final step will be to assess large cohorts and to analyze these data together with data from public resources using a bioinformatics approach. We could then develop diagnostic toolboxes for individual pathophysiology and select focused treatments or develop new ones.

Pain in chemotherapy-induced neuropathy--more than neuropathic?

Chemotherapy-induced neuropathy (CIN) is an adverse effect of chemotherapy. Pain in CIN might comprise neuropathic and nonneuropathic (ie, musculoskeletal) pain components, which might be characterized by pain patterns, electrophysiology, and somatosensory profiling. Included were 146 patients (100 female, 46 male; aged 56 ± 0.8 years) with CIN arising from different chemotherapy regimens. Patients were characterized clinically through nerve conduction studies (NCS) and quantitative sensory testing (QST). Questionnaires for pain (McGill) and anxiety/depression (Hospital Anxiety and Depression Scale) were supplied. Patients were followed-up after 17 days. Large- (61%) and mixed- (35%) fibre neuropathies were more frequent than small-fibre neuropathy (1.4%). The 5 major chemotherapeutic regimens impacted differently on large- but not on small-fibre function and did not predict painfulness. Chronic pain associated with CIN was reported in 41.7%. Painless and painful CIN did not differ in QST profiles or electrophysiological findings, but different somatosensory patterns were found in CIN subgroups (pain at rest [RestP], n = 25; movement-associated pain [MovP], n = 15; both pain characteristics [MovP+RestP], n = 21; or no pain [NonP], n = 85): small-fibre function (cold-detection threshold, CDT: z score: -1.46 ± 0.21, P < 0.01) was most impaired in RestP; mechanical hyperalgesia was exclusively found in MovP (z score: +0.81 ± 0.30, P < 0.05). "Anxiety" discriminated between painful and painless CIN; "CDT" and "anxiety" discriminated between patients with ongoing (RestP) and movement-associated pain (MovP) or pain components (MovP+RestP). The detrimental effect of chemotherapy on large fibres failed to differentiate painful from painless CIN. Patients stratified for musculoskeletal or neuropathic pain, however, differed in psychological and somatosensory parameters. This stratification might allow for the application of a more specific therapy.

The major brain endocannabinoid 2-AG controls neuropathic pain and mechanical hyperalgesia in patients with neuromyelitis optica

Recurrent myelitis is one of the predominant characteristics in patients with neuromyelitis optica (NMO). While paresis, visual loss, sensory deficits, and bladder dysfunction are well known symptoms in NMO patients, pain has been recognized only recently as another key symptom of the disease. Although spinal cord inflammation is a defining aspect of neuromyelitis, there is an almost complete lack of data on altered somatosensory function, including pain. Therefore, eleven consecutive patients with NMO were investigated regarding the presence and clinical characteristics of pain. All patients were examined clinically as well as by Quantitative Sensory Testing (QST) following the protocol of the German Research Network on Neuropathic Pain (DFNS). Additionally, plasma endocannabinoid levels and signs of chronic stress and depression were determined. Almost all patients (10/11) suffered from NMO-associated neuropathic pain for the last three months, and 8 out of 11 patients indicated relevant pain at the time of examination. Symptoms of neuropathic pain were reported in the vast majority of patients with NMO. Psychological testing revealed signs of marked depression. Compared to age and gender-matched healthy controls, QST revealed pronounced mechanical and thermal sensory loss, strongly correlated to ongoing pain suggesting the presence of deafferentation-induced neuropathic pain. Thermal hyperalgesia correlated to MRI-verified signs of spinal cord lesion. Heat hyperalgesia was highly correlated to the time since last relapse of NMO. Patients with NMO exhibited significant mechanical and thermal dysesthesia, namely dynamic mechanical allodynia and paradoxical heat sensation. Moreover, they presented frequently with either abnormal mechanical hypoalgesia or hyperalgesia, which depended significantly on plasma levels of the endogenous cannabinoid 2-arachidonoylglycerole (2-AG). These data emphasize the high prevalence of neuropathic pain and hyperalgesia in patients with NMO. The degree of mechanical hyperalgesia reflecting central sensitization of nociceptive pathways seems to be controlled by the major brain endocannabinoid 2-AG.