Neuropathic pain: diagnosis, pathophysiological mechanisms, and treatment. Lancet Neurol. 2010;9:807-819. [PMID: 20650402 DOI: 10.1016/s1474-4422(10)70143-5]

Magnetic Resonance Spectroscopic Analysis of Multifidus Muscle Lipid Contents and Association with Nociceptive Pain in Chronic Low Back Pain

Study Design

Cross-sectional study.

Purpose

This study aimed to analyze the differences in the lipid contents in chronic low back pain (CLBP) patients with nociceptive pain (NocP) and neuropathic pain (NeP) using magnetic resonance spectroscopy (MRS) of the multifidus muscle (Mm).

Overview of Literature

Early identification of the pain characteristics with CLBP is important because specific treatment approaches are required, depending on NocP and NeP.

Methods

The participants were 50 patients with CLBP (23 men and 27 women; mean age, 63.1±17.8 years; range, 41–79 years). We compared the Visual Analog Scale (VAS) scores, intramyocellular lipids (IMCLs) and extramyocellular lipids (EMCLs) of the Mm in NocP and NeP groups, as evaluated with the Japanese NeP screening questionnaire.

Results

The patients were categorized into the NocP (n=32) and NeP (n=18) groups. The mean VAS score of the NocP group was 59.3±3.1 mm and that of the NeP group was 73.6±4.6 mm. The mean VAS score was significantly higher in the NeP group as compared to that in the NocP group (p<0.01). As per the analysis of covariance for the VAS score, the mean IMCL levels of the Mm in the NocP and NeP groups were 722.3 mmol/L (95% confidence interval [CI], 611.4–833.1) and 484.8 mmol/L (95% CI, 381.1–588.5), respectively. The mean IMCL level was significantly higher in the NocP group than in the NeP group (p<0.05). The mean EMCL levels of the Mm for the NocP and NeP groups were 6,022.9 mmol/L (95% CI, 4,510.6–7,535.2) and 5,558.1 mmol/L (95% CI, 4,298.3–6,817.9), respectively; however, the difference was not significant (p=0.72).

Conclusions

The results indicated an association between the IMCL level of the Mm and NocP. Our results suggest that MRS of the Mm might be beneficial for the assessment of CLBP as well as appropriate targeted analgesic therapies.

Digital Pain Mapping and Tracking in Patients With Chronic Pain: Longitudinal Study

Background

Digital pain mapping allows for remote and ecological momentary assessment in patients over multiple time points spanning days to months. Frequent ecological assessments may reveal tendencies and fluctuations more clearly and provide insights into the trajectory of a patient’s pain.

Objective

The primary aim of this study is to remotely map and track the intensity and distribution of pain and discomfort (eg, burning, aching, and tingling) in patients with nonmalignant spinal referred pain over 12 weeks using a web-based app for digital pain mapping. The secondary aim is to explore the barriers of use by determining the differences in clinical and user characteristics between patients with good (regular users) and poor (nonregular users) reporting compliance.

Methods

Patients (N=91; n=53 women) with spinal referred pain were recruited using web-based and traditional in-house strategies. Patients were asked to submit weekly digital pain reports for 12 weeks. Each pain report consisted of digital pain drawings on a pseudo–three-dimensional body chart and pain intensity ratings. The pain drawings captured the distribution of pain and discomfort (pain quality descriptors) expressed as the total extent and location. Differences in weekly pain reports were explored using the total extent (pixels), current and usual pain intensity ratings, frequency of quality descriptor selection, and Jaccard similarity index. Validated e-questionnaires were completed at baseline to determine the patients’ characteristics (adapted Danish National Spine Register), disability (Oswestry Disability Index and Neck Disability Index), and pain catastrophizing (Pain Catastrophizing Scale) profiles. Barriers of use were assessed at 6 weeks using a health care–related usability and acceptance e-questionnaire and a self-developed technology-specific e-questionnaire to assess the accessibility and ease of access of the pain mapping app. Associations between total extent, pain intensity, disability, and catastrophizing were explored to further understand pain. Differences between regular and nonregular users were assessed to understand the pain mapping app reporting compliance.

Results

Fluctuations were identified in pain reports for total extent and pain intensity ratings (P<.001). However, quality descriptor selection (P=.99) and pain drawing (P=.49), compared using the Jaccard index, were similar over time. Interestingly, current pain intensity was greater than usual pain intensity (P<.001), suggesting that the timing of pain reporting coincided with a more intense pain experience than usual. Usability and acceptance were similar between regular and nonregular users. Regular users were younger (P<.001) and reported a larger total extent of pain than nonregular users (P<.001).

Conclusions

This is the first study to examine digital reports of pain intensity and distribution in patients with nonmalignant spinal referred pain remotely for a sustained period and barriers of use and compliance using a digital pain mapping app. Differences in age, pain distribution, and current pain intensity may influence reporting behavior and compliance.

Static mechanical allodynia in post-surgical neuropathic pain after breast cancer treatments

Objectives Static mechanical allodynia (SMA), i. e., pain caused by normally non-painful static pressure, is a prevalent manifestation of neuropathic pain (NP). Although SMA may significantly affect the patient's daily life, it is less well studied in the clinical context. We aimed to characterize SMA in women with chronic post-surgical NP (CPSNP) after breast cancer surgery. Our objective was to improve understanding of the clinical picture of this prevalent pain condition. This is a substudy of a previously published larger cohort of patients with intercostobrachial nerve injury after breast cancer surgery (Mustonen et al. Pain. 2019;160:246-56). Methods We studied SMA in 132 patients with CPSNP after breast cancer surgery. The presence, location, and intensity of SMA were assessed at clinical sensory examination. The patients gave self-reports of pain with the Brief Pain Inventory (BPI). We studied the association of SMA to type of surgery, oncological treatments, BMI, other pains, and psychological factors. General pain sensitivity was assessed by the cold pressor test. Results SMA was prevalent (84%) in this cohort whereas other forms of allodynia were scarce (6%). Moderate-to-severe SMA was frequently observed even in patients who reported mild pain in BPI. Breast and the side of chest were the most common locations of SMA. SMA was associated with breast surgery type, but not with psychological factors. Severe SMA, but not self-reported pain, was associated with lower cold pain tolerance. Conclusions SMA is prevalent in post-surgical NP after breast cancer surgery and it may represent a distinct NP phenotype. High intensities of SMA may signal the presence of central sensitization. Implications SMA should be considered when examining and treating patients with post-surgical NP after breast cancer surgery.

Painful metaphors: enactivism and art in qualitative research

Enactivism is an emerging theory for sense-making (cognition) with increasing applications to research and medicine. Enactivists reject the idea that sense-making is simply in the head or can be reduced to neural processes. Instead, enactivists argue that cognisers (people) are embodied and action-oriented, and that sense-making emerges from relational processes distributed across the brain-body-environment. We start this paper with an overview of a recently proposed enactive approach to pain. With rich theoretical and empirical roots in phenomenology and cognitive science, conceptualising pain as an enactive process is appealing as it overcomes the problematic dualist and reductionist nature of current pain theories and healthcare practices. Second, we discuss metaphor in the context of pain and enactivism, including a pain-related metaphor classification system. Third, we present and discuss five paintings created alongside an enactive study of clinical communication and the co-construction of pain-related meanings. Each painting represents pain-related metaphors delivered by clinicians during audio-recorded clinical appointments or discussed by clinicians and patients during interviews. We classify these metaphors, connecting them to enactive theory and relevant literature. The art, metaphors and associated narratives draw attention to the intertwined nature of language, meaning and pain. Of clinical relevance to primary and allied healthcare, we explore how clinicians' taken-for-granted pain-related metaphors can act as scaffolding for patients' pain and agency, for better or worse. We visually depict and give examples of clinical situations where metaphors became enactive, in that they were clinically reinforced and embodied through assessment and treatment. We conclude with research and clinical considerations, suggesting that enactive metaphor is a widely overlooked learning mechanism that clinicians could consider employing and intentionally shape.

Thermal quantitative sensory testing in burning mouth syndrome

OBJECTIVES

Subjects with burning mouth syndrome (BMS) have altered sensitivity and pain thresholds for thermal stimuli compared to a control group.

MATERIALS AND METHODS

Fourteen women and 6 men (average age = 62.60 years, median = 63.50) with BMS and a control group were tested using the method of thermal quantitative sensory testing (tQST) (tip, right, and left lateral border of the tongue, left thumb) to determine their heat/cold detection threshold (WDT/CDT) and heat/cold pain threshold (HPT/CPT).

RESULTS

Only the CPT values at the tip and both lateral border of the tongue show a statistically significant difference: tip of the tongue: sick = 12.0 ± 5.5 °C, median 14.2°C; healthy = 4.5 ± 2.9 °C; median = 6.4 °C; p = 0.000; right lateral border: sick = 8.55 ± 3.34 °C; healthy = 4.46 ± 1.90 °C; median 5.8 °C; p < 0.001; left lateral border: sick = 10.18 ± 3.94 °C¸ healthy = 4.15 ± 2.18 °C; median = 6.0 °C; p < 0.001.

CONCLUSIONS

BMS may be a combination of a dysfunction of free nociceptive nerve endings in the peripheral nervous system and impaired pain processing in the central nervous system.

CLINICAL RELEVANCE

This preliminary study provides hints to other causes of BMS. This offers the possibility of further therapeutic options.

Localization of prostaglandin E2 synthases and E-prostanoid receptors in the spinal cord in a rat model of neuropathic pain

Prostaglandin E2 (PGE2) is a lipid mediator which plays a role in the generation of inflammatory and neuropathic pain. In the peripheral nervous system, PGE2 sensitizes nociceptive afferent neurons through E-prostanoid (EP) receptors. In the central nervous system, PGE2 modulates pain sensitivity and contributes to the development of neuropathic pain. However, the distribution of PGE2 and EP receptors in the spinal cord remains unclear. In the present study, we examined the expression of PGE2 synthases (microsomal PGE synthase [mPGES]-1, mPGES-2, and cytosolic PGE synthase [cPGES]) and EP receptors (EP1-4) in a rat model of neuropathic pain. We identified that mPGES-1 mRNA was upregulated in spinal endothelial cells after nerve injury and exhibited co-localization with cyclooxygenase-2 (COX-2). We detected that mPGES-2 mRNA and cPGES mRNA were expressed in spinal neurons and noted that their expression level was not affected by nerve injury. With respect to EP receptors, EP2 mRNA and EP4 mRNA were expressed in spinal neurons in the dorsal horn. EP3 mRNA was expressed in motor neurons, whereas EP1 mRNA was not detected in the spinal cord. Intrathecal injection of tumor necrosis factor alpha (TNFα) upregulated mPGES-1 mRNA in blood vessels in the spinal cord. Intrathecal injection of a TNFα-neutralizing antibody partially inhibited the upregulation of mPGES-1 mRNA after nerve injury. These results indicate that PGE2 is synthesized by COX-2/mPGES-1 in spinal endothelial cells after nerve injury. These results suggest that in neuropathic pain condition, endothelial cell-derived PGE2 may act on EP2 and EP4 receptors on spinal neurons and modulate pain sensitivity.

Antiallodynic effect of PhAR-DBH-Me involves cannabinoid and TRPV1 receptors

The antiallodynic effect of PhAR-DBH-Me was evaluated on two models of neuropathic pain, and the potential roles of CB1, CB2, and TRPV1 receptors as molecular targets of PhAR-DBH-Me were studied. Female Wistar rats were submitted to L5/L6 spinal nerve ligation (SNL) or repeated doses of cisplatin (0.1 mg/kg, i.p.) to induce experimental neuropathy. Then, tactile allodynia was determined, and animals were treated with logarithmic doses of PhAR-DBH-Me (3.2-100 mg/kg, i.p.). To evaluate the mechanism of action of PhAR-DBH-Me, in silico studies using crystallized structures of CB1, CB2, and TRPV1 receptors were performed. To corroborate the computational insights, animals were intraperitoneally administrated with antagonists for CB1 (AM-251, 3 mg/kg), CB2 (AM-630, 1 mg/kg), and TRPV1 receptors (capsazepine, 3 mg/kg), 15 min before to PhAR-DBH-Me (100 mg/kg) administration. Vagal stimulation evoked on striated muscle contraction in esophagus, was used to elicited pharmacological response of PhAR-DBH-ME on nervous tissue. Systemic administration of PhAR-DBH-Me reduced the SNL- and cisplatin-induced allodynia. Docking studies suggested that PhAR-DBH-Me acts as an agonist for CB1, CB2, and TRPV1 receptors, with similar affinity to the endogenous ligand anandamide. Moreover antiallodynic effect of PhAR-DBH-Me was partially prevented by administration of AM-251 and AM-630, and completely prevented by capsazepine. Finally, PhAR-DBH-Me decreased the vagally evoked electrical response in esophagus rat. Taken together, results indicate that PhAR-DBH-Me induces an antiallodynic effect through partial activation of CB1 and CB2 receptors, as well as desensitization of TRPV1 receptors. Data also shed light on the novel vanilloid nature of the synthetic compound PhAR-DBH-Me.

The analgesic effect of metformin on paclitaxel-induced neuropathic pain model in rats: By considering pathological results

Background and Objective

Metformin (MET) has been used as an antidiabetic agent for type II diabetes. At the same time, recent researches have shown that the clinical improvement of MET is useful for nerve damage. In this study, we investigated the analgesic effect of MET in paclitaxel (PAC)-induced neuropathic pain.

Materials and Methods

Forty-two adult, female rats, Wistar strain weighing 220 ± 10 g were randomly divided into 5 experimental groups. PAC was intraperitoneally (IP) administered (2.0 mg/kg) for 4 groups every other day (0, 2, 4, and 6 days). By the 30^th day, MET (100, 200, and 400 mg/kg) was administered to 4 groups. Before and after treatment, basal pain threshold values were measured with Randall-Selitto analgesiometer test. At the end of experiment, pathological values were measured in selected regions including brain (motor cortex, M1), spinal cord (L4-L5), sciatic nerve, and muscle.

Results

According to our results, PAC-induced neuropathic pain reached to highest level at 14^th day. Four hundred milligram/kilogram concentration of MET remarkably decreased PAC-induced neuropathic pain. On the other hand, pathologic features have shown that PAC had significant pathological change in the brain and spinal cord while in the peripheral nerves and muscles had not shown any pathological change.

Conclusion

The pathological results of the current study for the first time demonstrated that MET beside of its antidiabetic effects reversed neuropathic pain induced by PAC. Consequently, this research can be promising for cancer patients that suffering from neuropathic pain induced by anticancer drugs.

Changes in expression of Kv7.5 and Kv7.2 channels in dorsal root ganglion neurons in the streptozotocin rat model of painful diabetic neuropathy

Diabetic peripheral neuropathic pain (DPNP), the most debilitating complication of diabetes mellitus, is resistant to current therapy. The pathogenesis of DPNP is still elusive, but several mechanisms have been proposed including abnormal hyperexcitability of dorsal root ganglion (DRG) neurons. The underlying molecular mechanisms of such aberrant hyperexcitability are incompletely understood. Using the streptozotocin (STZ) rat model of DPNP, we have recently provided evidence implicating neuronal K_v7 channels that normally exert a powerful stabilizing influence on neuronal excitability, in the abnormal hyperexcitability of DRG neurons and in pain hypersensitivity associated with DPNP. In the present immunohistochemical study, we sought to determine whether K_v7.2 and/or K_v7.5 channel expression is altered in DRG neurons in STZ rats. We found 35 days post-STZ: (1) a significant decrease in K_v7.5-immunoreactivity in small (<30 μm) DRG neurons (both IB4 positive and IB4 negative) and medium-sized (30-40 μm) neurons, and (2) a significant increase in K_v7.2-immunoreactivity in small (<30 μm) neurons, and a non-significant increase in medium/large neurons. The decrease in K_v7.5 channel expression in small and medium-sized DRG neurons in STZ rats is likely to contribute to the mechanisms of hyperexcitability of these neurons and thereby to the resulting pain hypersensitivity associated with DPNP. The upregulation of K_v7.2 subunit in small DRG neurons may be an activity dependent compensatory mechanism to limit STZ-induced hyperexcitability of DRG neurons and the associated pain hypersensitivity. The findings support the notion that K_v7 channels may represent a novel target for DPNP treatment.

Amifostine protects from the peripheral sensory neuropathy induced by oxaliplatin in mice

Sensory neuropathy is a dose-limiting side effect of oxaliplatin-based cancer treatment. This study investigated the antinociceptive effect of amifostine and its potential neuroprotective mechanisms on the oxaliplatin-related peripheral sensory neuropathy in mice. Oxaliplatin (1 mg/kg) was injected intravenously in Swiss albino male mice twice a week (total of nine injections), while amifostine (1, 5, 25, 50, and 100 mg/kg) was administered subcutaneously 30 min before oxaliplatin. Mechanical and thermal nociceptive tests were performed once a week for 49 days. Additionally, c-Fos, nitrotyrosine, and activating transcription factor 3 (ATF3) immunoexpressions were assessed in the dorsal root ganglia. In all doses, amifostine prevented the development of mechanical hyperalgesia and thermal allodynia induced by oxaliplatin (P<0.05). Amifostine at the dose of 25 mg/kg provided the best protection (P<0.05). Moreover, amifostine protected against neuronal hyperactivation, nitrosative stress, and neuronal damage in the dorsal root ganglia, detected by the reduced expression of c-Fos, nitrotyrosine, and ATF3 (P<0.05 vs the oxaliplatin-treated group). In conclusion, amifostine reduced the nociception induced by oxaliplatin in mice, suggesting the possible use of amifostine for the management of oxaliplatin-induced peripheral sensory neuropathy.

Chronic pain: a long-term sequela of epidermal necrolysis (Stevens-Johnson syndrome/toxic epidermal necrolysis) - prevalence, clinical characteristics and risk factors

BACKGROUND

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are associated with various sequelae. Chronic pain, one of these sequelae, has never been systematically evaluated.

OBJECTIVES AND METHODS

To assess the persistence of pain in a single-centre cohort of 113 consecutive patients with SJS/TEN. From this cohort, 81 patients were interviewed more than 1 year after the initial episode and included in the study. Data were collected according to standardized questionnaires.

RESULTS

From the 81 interviewed patients, 52 patients (64%) were painless and 29 patients (36%) were painful. Chronic pain syndrome was associated with a more severe initial acute phase of the disease (larger extent of detachment, higher SCORTEN, increased rate of admission in ICU and complications, and longer hospital stay). Pain was mainly located at the level of eyes (55%), mouth and lower limbs (38-41%), with a moderate daily intensity on average (4.7/10). The 'affective' descriptors prevailed over the 'sensory' descriptors, with the exception of burning and itching sensations. Finally, regarding provoked pain, mechanical allodynia (to brushing and pressure) was more marked than thermal allodynia.

DISCUSSION

The persistence of chronic pain after SJS/TEN is a common phenomenon. Sensory descriptors are consistent with sensitization of both small-diameter nerve fibres (burning and itching sensations) and large-diameter nerve fibres (mechanical allodynia), but the affective-emotional components of pain largely predominate.

CONCLUSIONS

Complex mechanisms lead to persistent pain as long-term sequela of SJS/TEN, among which mechanisms, psychological factors related to post-traumatic stress disorder probably play a key role.

Relief of Neuropathic Pain Through Epidermal Growth Factor Receptor Inhibition: A Randomized Proof-of-Concept Trial

OBJECTIVE

Case reports and a case series have described relief of neuropathic pain (NP) after treatment with epidermal growth factor receptor inhibitors (EGFR-Is). These observations are supported by preclinical findings. The aim of this trial was to explore a potential clinical signal supporting the therapeutic efficacy of EGFR-Is in NP.

METHODS

In a proof-of-concept trial using a randomized, double-blind, placebo-controlled design, 14 patients with severe, chronic, therapy-resistant NP due to compressed peripheral nerves or complex regional pain syndrome were randomized to receive a single infusion of the EGFR-I cetuximab and placebo in crossover design, followed by a single open-label cetuximab infusion.

RESULTS

The mean reduction in daily average pain scores three to seven days after single-blinded cetuximab infusion was 1.73 points (90% confidence interval [CI] = 0.80 to 2.66), conferring a 1.22-point greater reduction than placebo (90% CI = -0.10 to 2.54). Exploratory analyses suggested that pain reduction might be greater in the 14 days after treatment with blinded cetuximab than after placebo. The proportion of patients who reported ≥50% reduction in average pain three to seven days after cetuximab was 36% (14% after placebo), and comparison of overall pain reduction suggests a trend in favor of cetuximab. Skin rash (grade 1-2) was the most frequent side effect (12/14, 86%).

CONCLUSIONS

This small proof-of-concept evaluation of an EGFR-I against NP did not provide statistical evidence of efficacy. However, substantial reductions in pain were reported, and confidence intervals do not rule out a clinically meaningful treatment effect. Evaluation of EGFR-I against NP therefore warrants further investigation.

Persistent Rheb-induced mTORC1 activation in spinal cord neurons induces hypersensitivity in neuropathic pain

The small GTPase Ras homolog enriched in the brain (Rheb) can activate mammalian target of rapamycin (mTOR) and regulate the growth and cell cycle progression. We investigated the role of Rheb-mediated mTORC1 signaling in neuropathic pain. A chronic constriction injury (CCI) model was dopted. CCI induced obvious spinal Rheb expression and phosphorylation of mTOR, S6, and 4-E-BP1. Blocking mTORC1 signal with rapamycin alleviated the neuropathic pain and restored morphine efficacy in CCI model. Immunofluoresence showed a neuronal co-localization of CCI-induced Rheb and pS6. Rheb knockin mouse showed a similar behavioral phenotype as CCI. In spinal slice recording, CCI increased the firing frequency of neurons expressing HCN channels; inhibition of mTORC1 with rapamycin could reverse the increased spinal neuronal activity in neuropathic pain. Spinal Rheb is induced in neuropathic pain, which in turn active the mTORC1 signaling in CCI. Spinal Rheb-mTOR signal plays an important role in regulation of spinal sensitization in neuropathic pain, and targeting mTOR may give a new strategy for pain management.

Cannabidivarin for HIV-Associated Neuropathic Pain: A Randomized, Blinded, Controlled Clinical Trial

HIV remains a major burden to the health care system and neuropathic pain is the most common neurological complication of HIV infection. Because current treatment strategies often lack satisfying pain relief, cannabinoids (CBs) are discussed as a new option. We investigated cannabidivarin (CBDV) as treatment for HIV-associated neuropathic pain. We conducted a randomized, double-blind, placebo-controlled crossover study. Patients underwent two successive treatment phases (4 weeks each) and were treated with CBDV (400 mg/day) or placebo in a randomized order. A 3-week washout phase was designed to eliminate potential carry-over effects. Patients were followed up for 3 weeks after the end of the second treatment phase. The primary end point was pain intensity on an 11-point numeric rating scale, recorded in a diary. Secondary end points were additional pain medication, pain characteristics, and quality of life. We included 32 patients. The mean pain intensity under CBDV was 0.62 points higher compared with placebo (P = 0.16, 95% confidence interval -0.27 to 1.51). CBDV did not influence the amount of additional pain medication, pain characteristics, or quality of life. The incidence of adverse events was similar during both treatments. No suspected unexpected adverse reactions occurred during either treatment. CBDV was safe but failed to reduce neuropathic pain in patients with HIV. This may be explained by a lack of CB receptor activation, as indicated by preclinical experiments. Although a larger patient number might be desirable, we would not expect a change in the conclusions because the present differences are far from statistical significance. Therefore, we would currently not consider CBDV as a clinically meaningful treatment option for neuropathic pain.

Clinical perspective on pain in multiple sclerosis

Pain is an important and frequent symptom in multiple sclerosis (MS), which leads to a low quality of life, increased disability level, and lack of employment and mental health. Recently, studies have shown increased interest in pain in MS and there is a growing evidence of its prevalence. However, the literature suffers from lack of experimental studies focusing on pain reduction. This topical review summarizes the current knowledge about pain in MS with its definitions, assessments, treatments and rehabilitation within a holistic perspective.

Inflammatory cytokine expression in the skin of patients with postherpetic neuralgia

Objective

To assess the expression of inflammatory cytokines in the affected and normal skin of postherpetic neuralgia (PHN) patients.

Methods

Affected skin and normal skin samples were collected from PHN patients. Inflammatory cell infiltration in the dermis were evaluated by hematoxylin-eosin (HE) staining. A human inflammatory protein array containing 40 cytokines was used to assess expression differences between PHN and control skin. Enzyme linked immunosorbent assay (ELISA) kits were used to confirm cytokine expression in 10 PHN patients.

Results

HE staining showed that the epidermis of PHN skin was thicker than that of contralateral normal skin. Compared with normal skin, there was more infiltration of inflammatory cells into the dermis of PHN skin. The cytokine array detected the presence of 21/40 cytokines; however, only interleukin (IL)-1α showed differential expression between PHN skin and normal skin. ELISA results for IL-1α, IL-16, intercellular adhesion molecule-1, and monocyte chemoattractant protein-1 were consistent with those of cytokine arrays.

Conclusions

Expression of inflammatory cytokines in PHN skin was not significantly altered compared with normal skin. Chronic refractory pain in PHN is not necessarily associated with increased inflammation in the affected skin.

Neuropathic pain in spinal cord injury: topical analgesics as a possible treatment

STUDY DESIGN

Review of the literature and semi-structured interviews.

OBJECTIVE

To explore the possible use of topical analgesics for the treatment of neuropathic pain (NP) in spinal cord injury (SCI).

SETTING

Institute for Neuropathic Pain, Soest, The Netherlands.

METHODS

A review was performed of studies on topical analgesics for SCI-related NP published up to May 2019. In addition, eight persons with SCI-related NP who were treated with topical analgesics were interviewed in a semi-structured interview on their experience with topical analgesics.

RESULTS

Seven studies (five case reports and two case series) were found that evaluated the use of topical analgesics for SCI-related NP. None of the studies used a control treatment. Topical analgesics included baclofen, ketamine, lidocaine, capsaicin, and isosorbide dinitrate. All studies reported a decrease in NP over time. Persons interviewed were 49-72 years of age and all but one had an incomplete SCI. They used topical agents containing phenytoin, amitriptyline, baclofen, ketamine or loperamide. All showed a decrease in pain of at least 3 points on the 11-point numeric rating scale during this treatment.

DISCUSSION/CONCLUSIONS

Evidence on the use of topical analgesics in SCI is scarce. Case reports, case series and interviews suggest that the use of topical analgesics can be beneficial in treating SCI-related NP. Placebo-controlled studies are required to investigate the effect of topical analgesics on SCI-related NP.

Botulinum Neurotoxin for the Treatment of Neuropathic Pain

Botulinum neurotoxin is widely used for the treatment of central and peripherical neurological conditions. Initially used to treat strabismus, over the years its use has been expanded also to spasticity and other neurological disorders. This review summarizes the evidence from the published literature regarding its effect on neuropathic pain. Almost all investigations were performed using onabotulinum toxin type A (BoNT/A). Most studies provided positive results, even though toxin formulation, dose, dilution, injection techniques, and sites are heterogeneous across studies. Future larger, high-quality, specifically designed clinical trials are warranted to confirm botulinum neurotoxin efficacy in neuropathic pain.

Treatment of peripheral neuropathy: a multidisciplinary approach is necessary

The number of patients with peripheral neuropathy or neuropathic pain is increasing. The recommended treatment for peripheral neuropathy and neuropathic pain is proper medications, exercise, physical therapy, and support. Overly invasive interventions can be harmful rather than beneficial to patients. Many doctors do not understand the characteristics of peripheral neuropathy and neuropathic pain. Peripheral neuropathy is not a problem that is confined to a particular department. The most appropriate treatment is a combination of drug therapy, physical exercise, and psychological support. Thus, a multidisciplinary approach is necessary for the effective treatment of peripheral neuropathy and neuropathic pain.

Plasma Vitamin C Concentrations Were Negatively Associated with Tingling, Prickling or Pins and Needles Sensation in Patients with Postherpetic Neuralgia

Vitamin C deficiency increases the risk of postherpetic neuralgia (PHN). In this cross-sectional study, the relationships among plasma vitamin C concentrations, pain and Leeds assessment of neuropathic symptoms and signs (LANSS) items were investigated during their first pain clinic visit of 120 PHN patients. The factors associated with vitamin C deficiency were determined. Independent predictors of vitamin C deficiency were presented as adjusted odds ratios (AOR) and 95% confidence intervals (CI). The patients had a high prevalence (52.5%) of vitamin C deficiency. Their plasma vitamin C concentrations were negatively associated with spontaneous pain and tingling, prickling or pins and needles sensation according to the LANSS questionnaire. Based on the receiver operator characteristic curve, the cutoffs for plasma vitamin C to predict moderate-to-severe and severe symptoms of sharp sensation were <7.05 and <5.68 mg/L, respectively. By comparison, the patients well-nourished with vitamin C had lower incidences of sharp sensations, sharp pain, and reddish skin. Multivariate analyses revealed that vitamin C deficiency was associated with the low intake of fruit/vegetables (AOR 2.66, 95% CI 1.09–6.48, p = 0.032), peptic ulcer disease (AOR 3.25, 95% CI 1.28–8.28, p = 0.014), and smoking (AOR 3.60, 95% CI 1.33–9.77, p = 0.010). Future studies are needed to substantiate these findings.

ALIAmides Update: Palmitoylethanolamide and Its Formulations on Management of Peripheral Neuropathic Pain

Neuropathic pain results from lesions or diseases of the somatosensory nervous system and it remains largely difficult to treat. Peripheral neuropathic pain originates from injury to the peripheral nervous system (PNS) and manifests as a series of symptoms and complications, including allodynia and hyperalgesia. The aim of this review is to discuss a novel approach on neuropathic pain management, which is based on the knowledge of processes that underlie the development of peripheral neuropathic pain; in particular highlights the role of glia and mast cells in pain and neuroinflammation. ALIAmides (autacoid local injury antagonist amides) represent a group of endogenous bioactive lipids, including palmitoylethanolamide (PEA), which play a central role in numerous biological processes, including pain, inflammation, and lipid metabolism. These compounds are emerging thanks to their anti-inflammatory and anti-hyperalgesic effects, due to the down-regulation of activation of mast cells. Collectively, preclinical and clinical studies support the idea that ALIAmides merit further consideration as therapeutic approach for controlling inflammatory responses, pain, and related peripheral neuropathic pain.

Neuropathic Pain and Sickle Cell Disease: a Review of Pharmacologic Management

PURPOSE OF REVIEW

Sickle cell disease (SCD) remains among the most common and severe monogenic disorders present in the world today. Although sickle cell pain has been traditionally characterized as nociceptive, a significant portion of sickle cell patients has reported neuropathic pain symptoms. Our review article will discuss clinical aspects of SCD-related neuropathic pain, epidemiology of neuropathic pain among individuals with SCD, pain mechanisms, and current and future potential pharmacological interventions.

RECENT FINDINGS

Neuropathic pain in SCD is a complicated condition that often has a lifelong and significant negative impact on life; therefore, improved pain management is considered a significant and unmet need. Neuropathic pain mechanisms are heterogeneous, and the difficulty in determining their individual contribution to specific pain types may contribute to poor treatment outcomes in this population. Our review article outlines several pharmacological modalities which may be employed to treat neuropathic pain in SCD patients.

Comparison of clinical characteristics of post-refractive surgery-related and post-herpetic neuropathic corneal pain

Purpose:

To compare the clinical characteristics and in vivo confocal microscopy (IVCM) findings of patients with neuropathic corneal pain (NCP) due to refractive surgery (RS-NCP) and herpetic eye disease (H-NCP) to controls.

Methods:

Sixteen patients with RS-NCP and 7 patients with H-NCP, and 37 healthy reference age- and sex-matched healthy controls were included to the study. The medical records were reviewed for demographic features, detailed disease history, ocular surface disease index (OSDI), ocular pain assessment survey (OPAS) scores. IVCM images of patients were analyzed and compared to reference controls by two masked observers.

Results:

The mean pain intensity score for the last 24 h (5.1 ± 2.4 vs. 3.9 ± 1.2; p = 0.27), last 2 weeks (6.1 ± 2.5 vs. 4.8 ± 2.3; p = 0.13) for RS-NCP vs. H-NCP respectively, and quality of life scores (p = 0.23) were similar in both groups. Quality of life, especially mood (p = 0.06) and enjoying life/relations to others (p = 0.10) were affected in both groups, but were not statistically significant between groups. The mean total nerve density was lower in RS-NCP (5,702.4 ± 4,599.0 μm/mm²) compared to their respective controls (26,422.8 ± 4,491.0; p < 0.001) and in the H-NCP group (2,149.5 ± 2,985.9) compared to their respective controls (22,948.8 ± 3,169.0; p < 0.001). Alterations in DC density were similar between all groups (38.3 ± 48.0 cells/mm² in RS-NCP, 61.0 ± 76.9 in H-NCP, p = 0.95).

Conclusion:

Neuropathic corneal pain patients due to refractive surgery show similar clinical characteristics, pain levels, quality of life impact, and IVCM findings as patients with NCP due to herpetic eye disease.

Peripheral neuropathy and depressive symptoms: examining the association in a primary health care setting among persons with and without diabetes mellitus

PURPOSE

The purpose of this study was to measure the association between peripheral neuropathy symptoms and depressive symptoms among a sample of patients with and without diabetes mellitus (DM).

METHODS

Patients were administered the 15-item Michigan Neuropathy Screening Instrument (MNSI) and the patient health questionnaire depression scale (PHQ-8). Patients with an MNSI score ≥ 4 were categorized as having PN and patients with a PHQ-8 score ≥ 10 were considered to have current depression. Log-binomial regression was used to analyze the relationship between PN and depressive symptoms.

RESULTS

406 patients were included in the final analysis. There were no statistically significant differences by diabetes status in PN symptoms (Diabetes = 61.8%; No diabetes = 55.4%; p = .20) or in depression status (Diabetes = 37.6%; No diabetes = 36.6%; p =  .83). After adjustment for covariates, PN was associated with depression (aRR = 4.46; 95% CI 2.91,6.85) independent of diabetes status.

CONCLUSIONS

PN symptoms may be common among aging persons even in the absence of DM. Past literature and our study demonstrate that PN and depression are closely associated. More work is needed to understand the etiology and potential utility of intervention for depression symptoms among patients with neuropathy.

Prevalence, Patterns, and Correlates of Pain in Medically Hospitalized Pediatric Patients With Somatic Symptom and Related Disorders

BACKGROUND

Somatic symptom and related disorders (SSRDs) and pain are highly comorbid in the pediatric population. Little is known about the prevalence of pain and factors that may predispose and perpetuate pain in hospitalized youth with SSRD.

OBJECTIVE

To describe the prevalence of pain and widespread pain symptoms in hospitalized youth with SSRD and describe differences between patients who endorsed limited (1-4 sites) versus widespread (5-8 sites) pain.

METHODS

Retrospective chart reviews were conducted of pediatric patients with SSRD seen over a 32-month period at a tertiary pediatric hospital and assessed by the psychiatry consultation service. During admission, patients completed the Childhood Somatization Inventory, which assessed pain and other physical symptoms. Descriptive statistics, one-way analysis of variances, Pearson's χ², stepwise linear regressions, and internal consistency analyses were used.

RESULTS

Of the 219 patients (aged 8-18 y), 97% reported pain symptoms, and of those reporting pain (n = 213), 48% reported widespread pain. Patients with widespread pain had greater rates of comorbid depression (P = 0.012), neglect (P = 0.016), family psychiatric history (P = 0.013), diagnostic tests/procedures (P = 0.012), and prescribed opioid use (P = 0.016), when other medical and demographic factors were considered. When compared dichotomously to youth with limited pain, there was no difference in prevalence of medical conditions; however, patients with widespread pain had higher rates of trauma and stressor-related disorders (P = 0.017), sexual abuse (P = 0.031), emotional abuse (P = 0.041), and prior child protective service involvement (P = 0.011).

CONCLUSIONS

Pain symptoms and widespread pain are common in medically hospitalized youth with SSRD, with unique psychiatric and psychosocial factors associated with widespread pain.

Wound, pressure ulcer and burn guidelines - 1: Guidelines for wounds in general, second edition

The Japanese Dermatological Association prepared the clinical guidelines for the "Wound, pressure ulcer and burn guidelines", second edition, focusing on treatments. Among them, "Guidelines for wounds in general" is intended to provide the knowledge necessary to heal wounds, without focusing on particular disorders. It informs the basic principles of wound treatment, before explanations are provided in individual chapters of the guidelines. We updated all sections by collecting references published since the publication of the first edition. In particular, we included new wound dressings and topical medications. Additionally, we added "Question 6: How should wound-related pain be considered, and what should be done to control it?" as a new section addressing wound pain, which was not included in the first edition.

The role of microRNAs in neurons and neuroimmune communication in the dorsal root ganglia in chronic pain

Despite being a life-restricting condition, chronic pain remains poorly treated. A better understanding of the underlying mechanisms of chronic pain and thence development of innovative targets is therefore essential. Recently we have started to elucidate the importance of the role of microRNAs (miRs) in preclinical chronic pain. miRs are small, non-coding RNAs that regulate genes including those involved in nociceptive signalling. MiRs can exert their effects both intracellularly and extracellularly, the latter of which requires that they are released either as naked species or packaged in exosomes. Here we discuss changes in miR expression that occur in the dorsal root ganglia in murine models of chronic pain. We consider the downstream targets of changes in miR expression, including voltage-gated ion channels, as well as discuss extracellular consequences such as changes in macrophage phenotype that constitute of means by which neuron-immune cell crosstalk occurs. Such miR-mediated intracellular communication could provide a novel target for the treatment of chronic pain, which would be most effective if tailored to the specific cause of pain. Indeed, we conclude by reviewing evidence for the involvement of miRs in clinical cases of chronic pain, supporting the notion that tailored, miR-targeted therapies could prove to be an effective new strategy for the treatment of chronic pain clinically.

Early exposure to environmental enrichment protects male rats against neuropathic pain development after nerve injury

Because environmental elements modify chronic pain development and endogenous mechanisms of pain control are still a great therapeutic source, we investigated the effects of an early exposure to environmental enrichment (EE) in a translational model of neuropathic pain. Young male rats born and bred in an enriched environment, which did not count on running wheel, underwent chronic constriction injury (CCI) of sciatic nerve. EE abolished neuropathic pain behavior 14 days after CCI. Opioid receptors' antagonism reversed EE-analgesic effect. β-endorphin and met-enkephalin serum levels were increased only in EE-CCI group. Blockade of glucocorticoid receptors did not alter EE-analgesic effect, although corticosterone circulating levels were increased in EE animals. In the spinal cord, EE controlled CCI-induced serotonin increase. In DRG, EE blunted the expression of ATF-3 after CCI. Surprisingly, EE-CCI group showed a remarkable preservation of sciatic nerve fibers compared to NE-CCI group. This work demonstrated global effects induced by an EE protocol that explain, in part, the protective role of EE upon chronic noxious stimulation, reinforcing the importance of endogenous mechanisms in the prevention of chronic pain development.

5-HT1A receptor-mediated attenuation of heat hyperalgesia and mechanical allodynia by chrysin in mice with experimental mononeuropathy

BACKGROUND

Persistent neuropathic pain poses a health problem, for which effective therapy or antidote is in dire need. This work aimed to investigate the pain-relieving effect of chrysin, a natural flavonoid with monoamine oxidase inhibitory activity, in an experimental model of neuropathic pain and elucidate mechanism(s).

METHODS

Chronic constriction injury (CCI) was produced by loose ligation of sciatic nerve in mice. The pain-related behaviors were examined using von Frey test and Hargreaves test. The serotonin-related mechanisms were investigated by serotonin depletion with p-chlorophenylalanine (PCPA) and antagonist tests in vivo and in vitro.

RESULTS

Repeated treatment of CCI mice with chrysin (orally, two times per day for 2 weeks) ameliorated heat hyperalgesia and mechanical allodynia in a dose-dependent fashion (3-30 mg/kg). The chrysin-triggered pain relief seems serotonergically dependent, since its antihyperalgesic and antiallodynic actions were abolished by chemical depletion of serotonin by PCPA, whereas potentiated by 5-hydroxytryptophan (a precursor of 5-HT). Consistently, chrysin-treated neuropathic mice showed enhanced levels of spinal monoamines especially 5-HT, with depressed monoamine oxidase activity. Moreover, chrysin-evoked pain relief was preferentially counteracted by 5-HT_1A receptor antagonist WAY-100635 delivered systematically or spinally. In vitro, chrysin (0.1-10 nM) increased the maximum effect (Emax, shown as stimulation of [³⁵S] GTPγS binding) of 8-OH-DPAT, a 5-HT_1A agonist. Beneficially, chrysin was able to correct comorbid behavioral symptoms of depression and anxiety evoked by neuropathic pain, without causing hypertensive crisis (known as 'cheese reaction').

CONCLUSION

These findings confirm the antihyperalgesic and antiallodynic efficacies of chrysin, with spinal 5-HT_1A receptors being critically engaged.

Guideline "diagnosis and non interventional therapy of neuropathic pain" of the German Society of Neurology (deutsche Gesellschaft für Neurologie)

2019 the DGN (Deutsche Gesellschaft für Neurology) published a new guideline on the diagnosis and non-interventional therapy of neuropathic pain of any etiology excluding trigeminal neuralgia and CRPS (complex regional pain syndrome). Neuropathic pain occurs after lesion or damage of the somatosensory system. Besides clinical examination several diagnostic procedures are recommended to assess the function of nociceptive A-delta and C-Fibers (skin biopsy, quantitative sensory testing, Laser-evoked potentials, Pain-evoked potentials, corneal confocal microscopy, axon reflex testing). First line treatment in neuropathic pain is pregabalin, gabapentin, duloxetine and amitriptyline. Second choice drugs are topical capsaicin and lidocaine, which can also be considered as primary treatment in focal neuropathic pain. Opioids are considered as third choice treatment. Botulinum toxin can be considered as a third choice drug for focal limited pain in specialized centers only. Carbamazepine and oxcarbazepine cannot be generally  recommended, but might be helpful in single cases. In Germany, cannabinoids can be prescribed, but only after approval of reimbursement. However, the use is not recommended, and can only be considered as off-label therapy within a multimodal therapy concept.

The antiviral alkaloid berberine ameliorates neuropathic pain in rats with peripheral nerve injury

Neuropathic pain is a major public health problem. There is a need to develop safer and more effective analgesia compounds with less side effects. Berberine has been used to treat diarrhea and gastroenteritis due to its anti-microbial, anti-motility and anti-secretory properties. Berberine has also been reported to play an analgesic role in some pathological conditions of pain. However, the analgesic roles of berberine in neuropathic pain are still unclear. Therefore, this study aims to explore the analgesic effects of berberine in neuropathic pain. Partial sciatic nerve ligation (pSNL) was performed to create neuropathic pain model. Paw withdrawal responses to mechanical and thermal stimuli were measured using a set of electronic von Frey apparatus and hot plate, respectively. The time that rats spent licking, flinching and lifting its paw during 5 min following capsaicin application was recorded. mRNA and protein expression levels were examined by quantitative RT-PCR and western blot, respectively. Berberine administration (i.p.) increased both mechanical and thermal pain thresholds in a dose-dependent manner. Moreover, berberine administration reversed the mRNA and protein expression of TRPV1 in dorsal root ganglion neurons after peripheral nerve injury. In addition, berberine significantly inhibited capsaicin-induced pain behaviors. The amelioration of neuropathic pain by berberine may be associated with the down-regulation of TRPV1 in DRG of neuropathic pain rats. This study highlighted the potential of berberine in the treatment of neuropathic pain originated in the peripheral nervous system.

Quality of life effects of pain from para-lumbar- and lower extremity entrapment syndrome and carpal tunnel syndrome and comparison of the effectiveness of surgery

INTRODUCTION

We compared the preoperative quality of life (QOL) of patients with carpal tunnel syndrome, lower extremity-, and para-lumbar entrapment syndrome, and the effect of surgery on their QOL.

PATIENTS AND METHODS

We prospectively enrolled 66 consecutive patients who underwent surgery for carpal tunnel syndrome (group 1, n = 23), lower extremity entrapment syndrome (group 2, n = 22), and para-lumbar entrapment syndrome (group 3, n = 21). Their pre- and postoperative overall health status was assessed on the Medical Outcomes Study Short-Form 36 Health Survey, v2 (SF-36).

RESULTS

Except for the mental component summary, the preoperative score for items rated on the SF-36 was significantly lower in group 3 than in groups 1 and 2 (p < 0.05). In all 66 patients, the scores for bodily pain (BP) and the physical component summary (PCS) were significantly lower (p < 0.05) than the national standard, as was the score for physical functioning (PF) in groups 2 and 3. After surgery, PF of group 2 and PF, BP, and PCS of group 3 improved significantly (p < 0.05).

CONCLUSION

The detrimental QOL effects are stronger in patients with para-lumbar- or lower extremity entrapment syndrome than in patients with carpal tunnel syndrome.

Pathophysiologic Approach to Pain Therapy for Complex Pain Entities: A Narrative Review

Pain management is challenging for both clinicians and patients. In fact, pain patients are frequently undertreated or even completely untreated. Optimal treatment is based on targeting the underlying mechanisms of pain and tailoring the management modality for each patient using a personalized approach. This narrative review deals with pain conditions that have a complex underlying mechanism and need an individualized and frequently multifactorial approach to pain management. The research is based on previously conducted studies, and does not contain any studies with human participants or animals performed by any of the authors. This is not an exhaustive review of the current evidence. However, it provides the clinician with a perspective on pain therapy targeting the underlying pain mechanism(s). When dealing with complex pain conditions, the prudent physician benefits from having a deep knowledge of various underlying pain mechanisms in order to provide a plan for optimal pharmacological pain relief to patients.

Sensory profiles in women with neuropathic pain after breast cancer surgery

Purpose

We performed a detailed analysis of sensory function in patients with chronic post-surgical neuropathic pain (NP) after breast cancer treatments by quantitative sensory testing (QST) with DFNS (German Research Network on Neuropathic Pain) protocol and bed side examination (BE). The nature of sensory changes in peripheral NP may reflect distinct pathophysiological backgrounds that can guide the treatment choices. NP with sensory gain (i.e., hyperesthesia, hyperalgesia, allodynia) has been shown to respond to Na⁺-channel blockers (e.g., oxcarbazepine).

Methods

104 patients with at least “probable” NP in the surgical area were included. All patients had been treated for breast cancer 4–9 years ago and the handling of the intercostobrachial nerve (ICBN) was verified by the surgeon. QST was conducted at the site of NP in the surgical or nearby area and the corresponding contralateral area. BE covered the upper body and sensory abnormalities were marked on body maps and digitalized for area calculation. The outcomes of BE and QST were compared to assess the value of QST in the sensory examination of this patient group.

Results

Loss of function in both small and large fibers was a prominent feature in QST in the area of post-surgical NP. QST profiles did not differ between spared and resected ICBN. In BE, hypoesthesia on multiple modalities was highly prevalent. The presence of sensory gain in BE was associated with more intense pain.

Conclusions

Extensive sensory loss is characteristic for chronic post-surgical NP several years after treatment for breast cancer. These patients are unlikely to respond to Na⁺-channel blockers.

Cutaneous Aβ-Non-nociceptive, but Not C-Nociceptive, Dorsal Root Ganglion Neurons Exhibit Spontaneous Activity in the Streptozotocin Rat Model of Painful Diabetic Neuropathy in vivo

Diabetic peripheral neuropathic pain (DPNP) is the most devastating complication of diabetes mellitus. Unfortunately, successful therapy for DPNP remains a challenge because its pathogenesis is still elusive. However, DPNP is believed to be due partly to abnormal hyperexcitability of dorsal root ganglion (DRG) neurons, but the relative contributions of specific functional subtypes remain largely unknown. Here, using the strepotozotocin (STZ) rat model of DPNP induced by a STZ injection (60 mg/kg, i.p), and intracellular recordings of action potentials (APs) from DRG neurons in anesthetized rats, we examined electrophysiological changes in C-and Aβ-nociceptive and Aβ-low threshold mechanoreceptive (LTM) neurons that may contribute to DPNP. Compared with control, we found in STZ-rats with established pain hypersensitivity (5 weeks post-STZ) several significant changes including: (a) A 23% increase in the incidence of spontaneous activity (SA) in Aβ-LTMs (but not C-mechanosensitive nociceptors) that may cause dysesthesias/paresthesia suffered by DPNP patients, (b) membrane hyperpolarization and a ∼85% reduction in SA rate in Aβ-LTMs by Kv7 channel activation with retigabine (6 mg/kg, i.v.) suggesting that Kv7/M channels may be involved in mechanisms of SA generation in Aβ-LTMs, (c) decreases in AP duration and in duration and amplitude of afterhyperpolarization (AHP) in C-and/or Aβ-nociceptors. These faster AP and AHP kinetics may lead to repetitive firing and an increase in afferent input to the CNS and thereby contribute to DPNP development, and (d) a decrease in the electrical thresholds of Aβ-nociceptors that may contribute to their sensitization, and thus to the resulting hypersensitivity associated with DPNP.

Differential Expression of Acid - Sensing Ion Channels in Mouse Primary Afferents in Naïve and Injured Conditions

Injury and inflammation cause tissue acidosis, which is a common feature of various painful conditions. Acid-Sensing Ion channels (ASICs) are amongst the main excitatory channels activated by extracellular protons and expressed in the nervous system. Six transcripts of ASIC subunits including ASIC1a, ASIC1b, ASIC2a, ASIC2b, ASIC3, and ASIC4 are encoded by four genes (Asic1–4) and have been identified in rodents. Most ASIC subunits are present at substantial levels in primary sensory neurons of dorsal root ganglia (DRG) except for ASIC4. However, their expression pattern in DRG neurons remains largely unclear, mainly due to the lack of antibodies with appropriate specificity. In this study, we examined in detail the expression pattern of ASIC1-3 subunits, including splice variants, in different populations of DRG neurons in adult mice using an in situ hybridization technique (RNAscope) with high sensitivity and specificity. We found that in naïve condition, all five subunits examined were expressed in the majority of myelinated, NF200-immunoreactive, DRG neurons (NF200⁺). However, ASIC subunits showed a very different expression pattern among non-myelinated DRG neuronal subpopulations: ASIC1 and ASIC3 were only expressed in CGRP-immunoreactive neurons (CGRP⁺), ASIC2a was mostly expressed in the majority of IB4-binding neurons (IB4⁺), while ASIC2b was expressed in almost all non-myelinated DRG neurons. We also found that at least half of sensory neurons expressed multiple types of ASIC subunits, indicating prevalence of heteromeric channels. In mice with peripheral nerve injury, the expression level of ASIC1a and ASIC1b in L4 DRG and ASIC3 in L5 DRG were altered in CGRP⁺ neurons, but not in IB4⁺ neurons. Furthermore, the pattern of change varied among DRGs depending on their segmental level, which pointed to differential regulatory mechanisms between afferent types and anatomical location. The distinct expression pattern of ASIC transcripts in naïve condition, and the differential regulation of ASIC subunits after peripheral nerve injury, suggest that ASIC subunits are involved in separate sensory modalities.

Serotonergically dependent antihyperalgesic and antiallodynic effects of isoliquiritin in a mouse model of neuropathic pain

Chronic neuropathic pain poses a significant health problem worldwide, for which effective treatment is lacking. The current work aimed to investigate the potential analgesic effect of isoliquiritin, a flavonoid from Glycyrrhiza uralensis, against neuropathic pain and elucidate mechanisms. Male C57BL/6J mice were subjected to chronic constriction injury (CCI) by loose ligation of their sciatic nerves. Following CCI surgery, the neuropathic mice developed pain-like behaviors, as shown by thermal (heat) hyperalgesia in the Hargreaves test and tactile allodynia in the von Frey test. Repetitive treatment of CCI mice with isoliquiritin (p.o., twice per day for two weeks) ameliorated behavioral hyperalgesia to thermal (heat) stimuli and allodynia to tactile stimuli in a dose-dependent fashion (5, 15 and 45 mg/kg). The isoliquiritin-triggered analgesia seems serotonergically dependent, since its antihyperalgesic and antiallodynic actions were totally abolished by chemical depletion of spinal serotonin by p-chlorophenylalanine, whereas potentiated by 5-HTP (a precursor of 5-HT). Consistently, isoliquiritin-treated neuropathic mice showed escalated levels of spinal monoamines especially 5-HT, with depressed monoamine oxidase activity. Moreover, isoliquiritin-evoked antihyperalgesia and antiallodynia were preferentially counteracted by the 5-HT_1A receptor antagonist WAY-100635 delivered systematically or spinally. Of notable benefit, isoliquiritin was able to correct co-morbid behavioral symptoms of depression and anxiety evoked by neuropathic pain. Collectively, these findings demonstrate, for the first time, the therapeutic efficacy of isoliquiritin on neuropathic hypersensitivity, and this effect is dependent on the spinal serotonergic system and 5-HT_1A receptors.

Behavioral, Biochemical and Electrophysiological Changes in Spared Nerve Injury Model of Neuropathic Pain

Neuropathic pain is a pathological condition induced by a lesion or disease affecting the somatosensory system, with symptoms like allodynia and hyperalgesia. It has a multifaceted pathogenesis as it implicates several molecular signaling pathways involving peripheral and central nervous systems. Affective and cognitive dysfunctions have been reported as comorbidities of neuropathic pain states, supporting the notion that pain and mood disorders share some common pathogenetic mechanisms. The understanding of these pathophysiological mechanisms requires the development of animal models mimicking, as far as possible, clinical neuropathic pain symptoms. Among them, the Spared Nerve Injury (SNI) model has been largely characterized in terms of behavioral and functional alterations. This model is associated with changes in neuronal firing activity at spinal and supraspinal levels, and induces late neuropsychiatric disorders (such as anxious-like and depressive-like behaviors, and cognitive impairments) comparable to an advanced phase of neuropathy. The goal of this review is to summarize current findings in preclinical research, employing the SNI model as a tool for identifying pathophysiological mechanisms of neuropathic pain and testing pharmacological agent.

Neuropathic pain at diagnosis of head and neck squamous cell carcinoma

OBJECTIVE

To assess the prevalence and characteristics of neuropathic pain (NP) at diagnosis of head and neck squamous cell carcinoma (HNSCC) and its impact on nutritional status and treatment tolerance.

MATERIALS AND METHODS

Patients treated for HNSCC between January 1, 2018 and January 30, 2019 were included. Pain was assessed prospectively on the DN2 and NSPI scales. Epidemiological characteristics, nutritional status and treatment tolerance were collected. Two groups were distinguished according to absence or presence of neuropathic pain (NP-, NP+).

RESULTS

Sixty patients were included. NP prevalence at diagnosis was 54%, mainly involving locally advanced oral cavity and oropharyngeal tumors. There was a significant intergroup difference in nutritional status, with 62% malnutrition in NP+ versus 32% in NP- (p=0.0321). There was no such difference in tolerance.

CONCLUSION

NP is frequent at diagnosis of HNSCC. Early diagnosis on a simple validated score can help improve quality of life and nutritional status.

Identification of herbal categories active in pain disorder subtypes by machine learning help reveal novel molecular mechanisms of algesia

Chronic pain is highly prevalent and poorly controlled, of which the accurate underlying mechanisms need be further elucidated. Herbal drugs have been widely used for controlling various pain disorders. The systematic integration of pain herbal data resources might be promising to help investigate the molecular mechanisms of pain phenotypes. Here, we integrated large-scale bibliographic literatures and well-established data sources to obtain high-quality pain relevant herbal data (i.e. 426 pain related herbs with their targets). We used machine learning method to identify three distinct herb categories with their specific indications of symptoms, targets and enriched pathways, which were characterized by the efficacy of treatment to the chronic cough related neuropathic pain, the reproduction and autoimmune related pain, and the cancer pain, respectively. We further detected the novel pathophysiological mechanisms of the pain subtypes by network medicine approach to evaluate the interactions between herb targets and the pain disease modules. This work increased the understanding of the underlying molecular mechanisms of pain subtypes that herbal drugs are participating and with the ultimate aim of developing novel personalized drugs for pain disorders.

Cross-sectional study of patient satisfaction with oral analgesics in patients with chronic pain in Japan

BACKGROUND

Chronic pain is often difficult to treat, and many patients are not satisfied with analgesic treatment. The authors assessed patient satisfaction with oral analgesics in patients with chronic pain in Japan.

RESEARCH DESIGN AND METHODS

This was an observational cross-sectional study conducted in dispensing pharmacies. A patient satisfaction questionnaire survey was conducted in 781 patients prescribed one nonsteroidal anti-inflammatory drug (NSAID) or neuropathic pain (NeP) drug for at least 90 consecutive days. The primary endpoint was patient satisfaction with analgesics. The secondary endpoints were pain relief, activity of daily living (ADL) improvement and doctor-patient communication.

RESULTS

The proportions of patients who answered 'satisfied if anything' or better for patient satisfaction in the NSAID and NeP drug groups were 70.0% and 65.2%, respectively, whereas those of patients who answered 'satisfied' were 43.3% and 29.4%, respectively. The proportions of patients with improved pain relief, ADL improvement, and good doctor-patient communication were numerically higher than those of patients who answered 'satisfied if anything' or better.

CONCLUSIONS

Approximately two-thirds of the patients were satisfied with current analgesics. Patient satisfaction with oral analgesics could be influenced by multiple factors.

CLINICAL TRIAL REGISTRATION NUMBER

UMIN000036456.

Challenges of neuropathic pain: focus on diabetic neuropathy

Neuropathic pain is a frequent condition caused by a lesion or disease of the central or peripheral somatosensory nervous system. A frequent cause of peripheral neuropathic pain is diabetic neuropathy. Its complex pathophysiology is not yet fully elucidated, which contributes to underassessment and undertreatment. A mechanism-based treatment of painful diabetic neuropathy is challenging but phenotype-based stratification might be a way to develop individualized therapeutic concepts. Our goal is to review current knowledge of the pathophysiology of peripheral neuropathic pain, particularly painful diabetic neuropathy. We discuss state-of-the-art clinical assessment, validity of diagnostic and screening tools, and recommendations for the management of diabetic neuropathic pain including approaches towards personalized pain management. We also propose a research agenda for translational research including patient stratification for clinical trials and improved preclinical models in relation to current knowledge of underlying mechanisms.

Suppression of Superficial Microglial Activation by Spinal Cord Stimulation Attenuates Neuropathic Pain Following Sciatic Nerve Injury in Rats

We evaluated the mechanisms underlying the spinal cord stimulation (SCS)-induced analgesic effect on neuropathic pain following spared nerve injury (SNI). On day 3 after SNI, SCS was performed for 6 h by using electrodes paraspinally placed on the L4-S1 spinal cord. The effects of SCS and intraperitoneal minocycline administration on plantar mechanical sensitivity, microglial activation, and neuronal excitability in the L4 dorsal horn were assessed on day 3 after SNI. The somatosensory cortical responses to electrical stimulation of the hind paw on day 3 following SNI were examined by using in vivo optical imaging with a voltage-sensitive dye. On day 3 after SNI, plantar mechanical hypersensitivity and enhanced microglial activation were suppressed by minocycline or SCS, and L4 dorsal horn nociceptive neuronal hyperexcitability was suppressed by SCS. In vivo optical imaging also revealed that electrical stimulation of the hind paw-activated areas in the somatosensory cortex was decreased by SCS. The present findings suggest that SCS could suppress plantar SNI-induced neuropathic pain via inhibition of microglial activation in the L4 dorsal horn, which is involved in spinal neuronal hyperexcitability. SCS is likely to be a potential alternative and complementary medicine therapy to alleviate neuropathic pain following nerve injury.

Synchrotron radiation imaging analysis of neural damage in mouse soleus muscle

Damage to lower limb muscles requires accurate analysis of the muscular condition via objective microscopic diagnosis. However, microscopic tissue analysis may cause deformation of the tissue structure due to injury induced by external factors during tissue sectioning. To substantiate these muscle injuries, we used synchrotron X-ray imaging technology to project extremely small objects, provide three-dimensional microstructural analysis as extracted samples. In this study, we used mice as experimental animals to create soleus muscle models with various nerve injuries. We morphologically analyzed and quantified the damaged Section and Crush muscles, respectively, via three-dimensional visualization using synchrotron radiation X-ray imaging to diagnose muscle injury. Results of this study can also be used as basic data in the medical imaging field.