Using stratified medicine to understand, diagnose, and treat neuropathic pain

TRPA1 Inhibition Effects by 3-Phenylcoumarin Derivatives

Transient receptor potential ankyrin 1 (TRPA1) protein plays an important role in the inflammatory response, and it has been associated with different pain conditions and pain-related diseases, making TRPA1 a valid target for painkillers. In this study, we identified potential TRPA1 inhibitors and located their binding sites utilizing computer-aided drug design (CADD) techniques. The designed 3-phenylcoumarin-based TRPA1 inhibitors were successfully synthesized using a microwave assisted synthetic strategy. 3-(3-Bromophenyl)-7-acetoxycoumarin (5), 7-hydroxy-3-(3-hydroxyphenyl)coumarin (12) and 3-(3-hydroxyphenyl)coumarin (23) all showed inhibitory activity toward TRPA1 in vitro. Compound 5 also decreased the size and formation of breast cancer cells. Hence, targeting TRPA1 may represent a promising alternative for the treatment of pain and inflammation.

Effects of Ultrasound-Guided Thoracic Paravertebral Nerve Block Combined with Perineural or IV Dexmedetomidine on Acute and Chronic Pain After Thoracoscopic Resection of Lung Lesions: A Double-Blind Randomized Trial

Background

Thoracic paravertebral block (TPVB) analgesia can be prolonged by local anesthetic adjuvants such as dexmedetomidine. This study aimed to evaluate the two administration routes of dexmedetomidine on acute pain and chronic neuropathic pain (NeuP) prevention compared with no dexmedetomidine.

Methods

A total of 216 patients were randomized to receive TPVB using 0.4% ropivacaine alone (R Group), with perineural dexmedetomidine 0.5 μg·kg-1 (RD0.5 Group) or 1.0 μg·kg-1 (RD1.0 Group), or intravenous (IV) dexmedetomidine 0.5 μg·kg-1·h-1 (RDiv Group). The primary outcome was the incidence of chronic NeuP, defined as a Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) pain score > 12 points at 3-month after surgery.

Results

(1) For the primary outcome, RD0.5 Group and RD1.0 Group demonstrated a decreased incidence of chronic NeuP at 3-month after surgery; (2) Compared with R Group, RDiv Group, RD0.5 Group, and RD1.0 Group can reduce VAS scores at rest and movement and Prince-Henry Pain scores at 12 and 24-h after surgery, the consumption of oral morphine equivalent (OME) and improve QOD-15 at POD1; (3) Compared with RDiv Group, RD0.5 Group and RD1.0 Group can reduce VAS scores at rest and movement and Prince-Henry Pain scores at 12 and 24-h after surgery, the consumption of postoperative OME and improve QOD-15 at POD1; (4) Compared with RD0.5 Group, RD1.0 Group effectively reduced VAS scores at rest at 12 and 24-h after surgery, VAS scores in movement and Prince-Henry Pain scores at 12-h after surgery. However, RD1.0 Group showed an increased incidence of drowsiness.

Conclusion

Perineural or IV dexmedetomidine are similarly effective in reducing acute pain, but only perineural dexmedetomidine reduced chronic NeuP. Moreover, considering postoperative complications such as drowsiness, perineural dexmedetomidine (0.5 μg·kg-1) may be a more appropriate choice.

Clinical Trial Registration

Chinese Clinical Trial Registry (ChiCTR2200058982).

Systemic low-grade C-reactive protein is associated with proximal symptom spread in carpal tunnel syndrome

Introduction

Neuropathic pain is a highly prevalent condition associated with persistent disability. Some patients with neuropathic pain experience symptom spread outside neuroanatomical boundaries; these patients report more severe sensory symptoms and greater disability. However, the mechanisms behind such symptom spread are not fully understood.

Objective

We used pre-surgical carpal tunnel syndrome (CTS) as a human model system of neuropathic pain to identify differences in the concentration of serologic inflammatory mediators between patients with CTS with territorial symptoms and those with proximal symptom spread to either the elbow or shoulder/neck.

Methods

We performed a post-hoc analysis, comparing levels of serologic inflammatory mediators in a discovery cohort among 3 symptoms spread profiles (n = 55; n = 25 no spread, n = 21 spread to elbow, n = 9 spread to shoulder/neck). We then de-novo analysed the significantly dysregulated mediators in an independent validation cohort (n = 72; n = 34 no spread, n = 16 spread to elbow, n = 22 spread to shoulder/neck).

Results

The discovery cohort revealed higher serum concentrations of C-reactive protein (CRP) and interleukin-6 in patients with any symptom spread proximal to the wrist; interferon-γ was higher in patients with symptom spread to the elbow compared with those without proximal spread. The validation study replicated the association of higher CRP concentrations in patients with proximal spread to the elbow (no spread: median [interquartile range] 2.5 [5.4]; spread to elbow 6.2 [4.6]; spread to shoulder/neck 2.6 [3.7], P = 0.006). No other markers replicated in the validation cohort.

Conclusions

Our findings suggest that proximal symptom spread in the context of neuropathic symptoms is associated with low-grade inflammation.

A diminished sciatic nerve structural integrity is associated with distinct peripheral sensory phenotypes in individuals with type 2 diabetes

AIMS/HYPOTHESIS

Quantitative sensory testing (QST) allows the identification of individuals with rapid progression of diabetic sensorimotor polyneuropathy (DSPN) based on certain sensory phenotypes. Hence, the aim of this study was to investigate the relationship of these phenotypes with the structural integrity of the sciatic nerve among individuals with type 2 diabetes.

METHODS

Seventy-six individuals with type 2 diabetes took part in this cross-sectional study and underwent QST of the right foot and high-resolution magnetic resonance neurography including diffusion tensor imaging of the right distal sciatic nerve to determine the sciatic nerve fractional anisotropy (FA) and cross-sectional area (CSA), both of which serve as markers of structural integrity of peripheral nerves. Participants were then assigned to four sensory phenotypes (participants with type 2 diabetes and healthy sensory profile [HSP], thermal hyperalgesia [TH], mechanical hyperalgesia [MH], sensory loss [SL]) by a standardised sorting algorithm based on QST.

RESULTS

Objective neurological deficits showed a gradual increase across HSP, TH, MH and SL groups, being higher in MH compared with HSP and in SL compared with HSP and TH. The number of participants categorised as HSP, TH, MH and SL was 16, 24, 17 and 19, respectively. There was a gradual decrease of the sciatic nerve's FA (HSP 0.444, TH 0.437, MH 0.395, SL 0.382; p=0.005) and increase of CSA (HSP 21.7, TH 21.5, MH 25.9, SL 25.8 mm2; p=0.011) across the four phenotypes. Further, MH and SL were associated with a lower sciatic FA (MH unstandardised regression coefficient [B]=-0.048 [95% CI -0.091, -0.006], p=0.027; SL B=-0.062 [95% CI -0.103, -0.020], p=0.004) and CSA (MH β=4.3 [95% CI 0.5, 8.0], p=0.028; SL B=4.0 [95% CI 0.4, 7.7], p=0.032) in a multivariable regression analysis. The sciatic FA correlated negatively with the sciatic CSA (r=-0.35, p=0.002) and markers of microvascular damage (high-sensitivity troponin T, urine albumin/creatinine ratio).

CONCLUSIONS/INTERPRETATION

The most severe sensory phenotypes of DSPN (MH and SL) showed diminishing sciatic nerve structural integrity indexed by lower FA, likely representing progressive axonal loss, as well as increasing CSA of the sciatic nerve, which cannot be detected in individuals with TH. Individuals with type 2 diabetes may experience a predefined cascade of nerve fibre damage in the course of the disease, from healthy to TH, to MH and finally SL, while structural changes in the proximal nerve seem to precede the sensory loss of peripheral nerves and indicate potential targets for the prevention of end-stage DSPN.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03022721.

Central neuropathic pain

Central neuropathic pain arises from a lesion or disease of the central somatosensory nervous system such as brain injury, spinal cord injury, stroke, multiple sclerosis or related neuroinflammatory conditions. The incidence of central neuropathic pain differs based on its underlying cause. Individuals with spinal cord injury are at the highest risk; however, central post-stroke pain is the most prevalent form of central neuropathic pain worldwide. The mechanisms that underlie central neuropathic pain are not fully understood, but the pathophysiology likely involves intricate interactions and maladaptive plasticity within spinal circuits and brain circuits associated with nociception and antinociception coupled with neuronal hyperexcitability. Modulation of neuronal activity, neuron-glia and neuro-immune interactions and targeting pain-related alterations in brain connectivity, represent potential therapeutic approaches. Current evidence-based pharmacological treatments include antidepressants and gabapentinoids as first-line options. Non-pharmacological pain management options include self-management strategies, exercise and neuromodulation. A comprehensive pain history and clinical examination form the foundation of central neuropathic pain classification, identification of potential risk factors and stratification of patients for clinical trials. Advanced neurophysiological and neuroimaging techniques hold promise to improve the understanding of mechanisms that underlie central neuropathic pain and as predictive biomarkers of treatment outcome.

Introduction to a special issue on big data and pain

This special issue comprised 7 articles from leaders in the field that focus on "big pain data", the large datasets and the associated methods for data analysis that are currently emerging in pain research. This collection of articles highlights the power and potential as well as points of caution that multi-disciplinary research utilising big data and their associated methods and interpretations present for pain research.

Peripheral mechanisms of peripheral neuropathic pain

Peripheral neuropathic pain (PNP), neuropathic pain that arises from a damage or disease affecting the peripheral nervous system, is associated with an extremely large disease burden, and there is an increasing and urgent need for new therapies for treating this disorder. In this review we have highlighted therapeutic targets that may be translated into disease modifying therapies for PNP associated with peripheral neuropathy. We have also discussed how genetic studies and novel technologies, such as optogenetics, chemogenetics and single-cell RNA-sequencing, have been increasingly successful in revealing novel mechanisms underlying PNP. Additionally, consideration of the role of non-neuronal cells and communication between the skin and sensory afferents is presented to highlight the potential use of drug treatment that could be applied topically, bypassing drug side effects. We conclude by discussing the current difficulties to the development of effective new therapies and, most importantly, how we might improve the translation of targets for peripheral neuropathic pain identified from studies in animal models to the clinic.

Prolonged continuous theta burst stimulation increases motor corticospinal excitability and intracortical inhibition in patients with neuropathic pain: An exploratory, single-blinded, randomized controlled trial

OBJECTIVES

A new paradigm for Transcranial Magnetic Stimulation (TMS), referred to as prolonged continuous theta burst stimulation (pcTBS), has recently received attention in the literature because of its advantages over high frequency repetitive TMS (HF-rTMS). Clinical advantages include less time per intervention session and the effects appear to be more robust and reproducible than HF-rTMS to modulate cortical excitability. HF-rTMS targeted at the primary motor cortex (M1) has demonstrated analgesic effects in patients with neuropathic pain but their mechanisms of action are unclear and pcTBS has been studied in healthy subjects only. This study examined the neural mechanisms that have been proposed to play a role in explaining the effects of pcTBS targeted at the M1 and DLPFC brain regions in neuropathic pain (NP) patients with Type 2 diabetes.

METHODS

Forty-two patients with painful diabetic neuropathy were randomized to receive a single session of pcTBS targeted at the left M1 or left DLPFC. pcTBS stimulation consisted of 1,200 pulses delivered in 1 min and 44 s with a 35-45 min gap between sham and active pcTBS stimulation. Both the activity of the descending pain system which was examined using conditioned pain modulation and the activity of the ascending pain system which was assessed using temporal summation of pain were recorded using a handheld pressure algometer by measuring pressure pain thresholds. The amplitude of the motor evoked potential (MEP) was used to measure motor corticospinal excitability and GABA activity was assessed using short (SICI) and long intracortical inhibition (LICI). All these measurements were performed at baseline and post-pcTBS stimulation.

RESULTS

Following a single session of pcTBS targeted at M1 and DLPFC, there was no change in BPI-DN scores and on the activity of the descending (measured using conditioned pain modulation) and ascending pain systems (measured using temporal summation of pain) compared to baseline but there was a significant improvement of >13% in perception of acute pain intensity, increased motor corticospinal excitability (measured using MEP amplitude) and intracortical inhibition (measured using SICI and LICI).

CONCLUSION

In patients with NP, a single session of pcTBS targeted at the M1 and DLPFC modulated the neurophysiological mechanisms related to motor corticospinal excitability and neurochemical mechanisms linked to GABA activity, but it did not modulate the activity of the ascending and descending endogenous modulatory systems. In addition, although BPI-DN scores did not change, there was a 13% improvement in self-reported perception of acute pain intensity.

Spinal disinhibition: evidence for a hyperpathia phenotype in painful diabetic neuropathy

The dominant sensory phenotype in patients with diabetic polyneuropathy and neuropathic pain is a loss of function. This raises questions as to which mechanisms underlie pain generation in the face of potentially reduced afferent input. One potential mechanism is spinal disinhibition, whereby a loss of spinal inhibition leads to increased ascending nociceptive drive due to amplification of, or a failure to suppress, incoming signals from the periphery. We aimed to explore whether a putative biomarker of spinal disinhibition, impaired rate-dependent depression of the Hoffmann reflex, is associated with a mechanistically appropriate and distinct pain phenotype in patients with painful diabetic neuropathy. In this cross-sectional study, 93 patients with diabetic neuropathy underwent testing of Hoffmann reflex rate-dependent depression and detailed clinical and sensory phenotyping, including quantitative sensory testing. Compared to neuropathic patients without pain, patients with painful diabetic neuropathy had impaired Hoffmann reflex rate-dependent depression at 1, 2 and 3 Hz (P ≤ 0.001). Patients with painful diabetic neuropathy exhibited an overall loss of function profile on quantitative sensory testing. However, within the painful diabetic neuropathy group, cluster analysis showed evidence of greater spinal disinhibition associated with greater mechanical pain sensitivity, relative heat hyperalgesia and higher ratings of spontaneous burning pain. These findings support spinal disinhibition as an important centrally mediated pain amplification mechanism in painful diabetic neuropathy. Furthermore, our analysis indicates an association between spinal disinhibition and a distinct phenotype, arguably akin to hyperpathia, with combined loss and relative gain of function leading to increasing nociceptive drive.

Neuroimaging reveals a potential brain-based pre-existing mechanism that confers vulnerability to development of chronic painful chemotherapy-induced peripheral neuropathy

BACKGROUND

Chemotherapy-induced peripheral neuropathy (CIPN) is a debilitating condition impacting 30% of cancer survivors. This study is the first to explore whether a brain-based vulnerability to chronic sensory CIPN exists.

METHODS

This prospective, multicentre cohort study recruited from three sites across Scotland. Brain functional MRI (fMRI) scans (3 Tesla) were carried out on chemotherapy naïve patients at a single fMRI centre in Edinburgh, Scotland. Nociceptive stimuli (with a 256 mN monofilament) were administered during the fMRI. Development of chronic sensory/painful CIPN (CIPN+) was determined based upon European Organization for Research and Treatment of Cancer Quality of Life Questionnaire Chemotherapy-Induced Peripheral Neuropathy 20 changes conducted 9 months after chemotherapy, and imaging data analysed using standard software.

RESULTS

Of 30 patients recruited (two lung, nine gynaecological, and 19 colorectal malignancies), data from 20 patients at 9 months after chemotherapy was available for analysis. Twelve were classified as CIPN+ (mean age, 63.2[9.6] yr, 9.6; six female), eight as CIPN- (mean age 62.9 [SD 5.5] yr, four female). In response to punctate stimulation, group contrast analysis showed that CIPN+ compared with CIPN- had robust activity in sensory, motor, attentional, and affective brain regions. An a priori chosen region-of-interest analysis focusing on the periaqueductal grey, an area hypothesised as relevant for developing CIPN+, showed significantly increased responses in CIPN- compared with CIPN+ patients. No difference in subcortical volumes between CIPN+ and CIPN- patients was detected.

CONCLUSIONS

Before administration of any chemotherapy or appearance of CIPN symptoms, we observed altered patterns of brain activity in response to nociceptive stimulation in patients who later developed chronic sensory CIPN. This suggests the possibility of a pre-existing vulnerability to developing CIPN centred on brainstem regions of the descending pain modulatory system.

The power of integrating data: advancing pain research using meta-analysis

Publications related to pain research have increased significantly in recent years. The abundance of new evidence creates challenges staying up to date with the latest information. A comprehensive understanding of the literature is important for both clinicians and investigators involved in pain research. One commonly used method to combine and analyse data in health care research is meta-analysis. The primary aim of a meta-analysis is to quantitatively synthesise the results of multiple studies focused on the same research question. Meta-analysis is a powerful tool that can be used to advance pain research. However, there are inherent challenges when combining data from multiple sources. There are also numerous models and statistical considerations when undertaking a meta-analysis. This review aims to discuss the planning and preparation for completing a meta-analysis, review commonly used meta-analysis models, and evaluate the clinical implications of meta-analysis in pain research.

Co-occurrence and metabolic biomarkers of sensory and motor subtypes of peripheral neuropathy from paclitaxel

PURPOSE

Chemotherapy-induced peripheral neuropathy (CIPN) is the major treatment-limiting toxicity of paclitaxel, which predominantly presents as sensory symptoms, with motor symptoms in some patients. Differentiating CIPN into subtypes has been recommended to direct CIPN research. The objective of this study was to investigate whether sensory and motor CIPN are distinct subtypes with different predictive biomarkers in patients with breast cancer receiving paclitaxel.

METHODS

Data were from a prospective cohort of 60 patients with breast cancer receiving up to 12 weekly infusions of 80 mg/m2 paclitaxel (NCT02338115). European Organisation for Research and Treatment of Cancer Quality of Life questionnaire CIPN20 was used to evaluate CIPN. Clusters of the time course of sensory (CIPNS), motor (CIPNM), and the difference between sensory and motor (CIPNS-CIPNM) were identified using k-means clustering on principal component scores. Predictive metabolomic biomarkers of maximum CIPNS and CIPNM were investigated using linear regressions adjusted for baseline CIPN, paclitaxel pharmacokinetics, and body mass index.

RESULTS

More sensory than motor CIPN was found (CIPNS change: mean = 10.8, ranged [-3.3, 52.1]; CIPNM change: mean = 3.5, range: [-7.5, 35.0]). Three groups were identified with No CIPN, Mixed CIPN, and Sensory-dominant CIPN (maximum CIPNS: mean = 12.7 vs. 40.9 vs. 74.3, p < 0.001; maximum CIPNM: mean = 5.4 vs. 25.5 vs. 36.1, p < 0.001; average CIPNS-CIPNM: mean = 2.8 vs. 5.8 vs. 24.9, p < 0.001). Biomarkers of motor CIPN were similar to previously identified biomarkers of sensory CIPN, including lower serum histidine (p = 0.029).

CONCLUSION

Our findings suggest that sensory and motor CIPN co-occur and may not have differentiating metabolic biomarkers. These findings need to be validated in larger cohorts of patients treated with paclitaxel and other neurotoxic agents to determine the optimal approach to predict, prevent, and treat CIPN and improve patients' outcomes.

Classification of painful or painless diabetic peripheral neuropathy and identification of the most powerful predictors using machine learning models in large cross-sectional cohorts

BACKGROUND

To improve the treatment of painful Diabetic Peripheral Neuropathy (DPN) and associated co-morbidities, a better understanding of the pathophysiology and risk factors for painful DPN is required. Using harmonised cohorts (N = 1230) we have built models that classify painful versus painless DPN using quality of life (EQ5D), lifestyle (smoking, alcohol consumption), demographics (age, gender), personality and psychology traits (anxiety, depression, personality traits), biochemical (HbA1c) and clinical variables (BMI, hospital stay and trauma at young age) as predictors.

METHODS

The Random Forest, Adaptive Regression Splines and Naive Bayes machine learning models were trained for classifying painful/painless DPN. Their performance was estimated using cross-validation in large cross-sectional cohorts (N = 935) and externally validated in a large population-based cohort (N = 295). Variables were ranked for importance using model specific metrics and marginal effects of predictors were aggregated and assessed at the global level. Model selection was carried out using the Mathews Correlation Coefficient (MCC) and model performance was quantified in the validation set using MCC, the area under the precision/recall curve (AUPRC) and accuracy.

RESULTS

Random Forest (MCC = 0.28, AUPRC = 0.76) and Adaptive Regression Splines (MCC = 0.29, AUPRC = 0.77) were the best performing models and showed the smallest reduction in performance between the training and validation dataset. EQ5D index, the 10-item personality dimensions, HbA1c, Depression and Anxiety t-scores, age and Body Mass Index were consistently amongst the most powerful predictors in classifying painful vs painless DPN.

CONCLUSIONS

Machine learning models trained on large cross-sectional cohorts were able to accurately classify painful or painless DPN on an independent population-based dataset. Painful DPN is associated with more depression, anxiety and certain personality traits. It is also associated with poorer self-reported quality of life, younger age, poor glucose control and high Body Mass Index (BMI). The models showed good performance in realistic conditions in the presence of missing values and noisy datasets. These models can be used either in the clinical context to assist patient stratification based on the risk of painful DPN or return broad risk categories based on user input. Model's performance and calibration suggest that in both cases they could potentially improve diagnosis and outcomes by changing modifiable factors like BMI and HbA1c control and institute earlier preventive or supportive measures like psychological interventions.

Transcriptomic Analysis of Trigeminal Ganglion and Spinal Trigeminal Nucleus Caudalis in Mice with Inflammatory Temporomandibular Joint Pain

BACKGROUND

Persistent facial pain heavily impacts the quality of life in patients with temporomandibular joint (TMJ) disorders. Previous studies have demonstrated that long non-coding ribonucleic acid (lncRNA) is an important regulator of pain. In this study, we aimed to analyze lncRNA expression in the whole transcriptome of trigeminal ganglia (TG) and spinal trigeminal nucleus caudalis (Sp5C) in a chronic inflammatory TMJ pain mouse model.

METHODS

Chronic inflammatory TMJ pain was induced by intra-TMJ injection of complete Freund's adjuvant (CFA). Mouse TG and Sp5C tissues were harvested on day 4 after CFA injection. The lncRNA expression patterns in the whole transcriptome of TG and Sp5C were profiled with RNA sequencing.

RESULTS

We observed that 38 lncRNAs and 849 mRNAs were differentially expressed after CFA treatment. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis further revealed relationships among those differentially expressed lncRNAs and mRNAs and their potential functions. Specific categories of biological process, cellular processes, and molecular function of the differentially expressed transcripts were ascertained.

CONCLUSION

Our results suggest that lncRNA expression in the whole transcriptome of trigeminal nociceptive system could contribute to the molecular mechanisms that underlie chronic inflammatory TMJ pain.

Pharmacotherapy of Painful Diabetic Neuropathy: A Clinical Update

The rising prevalence of diabetes mellitus (DM) leads on to an increase in chronic diabetic complications. Diabetic peripheral neuropathies (DPNs) are common chronic complications of diabetes. Distal symmetric polyneuropathy is the most prevalent form. Most patients with DPN will remain pain-free; however, painful DPN (PDPN) occurs in 6-34% of all DM patients and is associated with reduced health-related-quality-of-life and substantial economic burden. Symptomatic treatment of PDPN and diabetic autonomic neuropathy is the key treatment goals. Using certain patient related characteristics, subjects with PDPN can be stratified and assigned targeted therapies to produce better pain outcomes. The aim of this review is to discuss the various pathogenetic mechanisms of DPN with special reference to the mechanisms leading to PDPN and the various pharmacological and non-pharmacological therapies available for its management. Recommended pharmacological therapies include anticonvulsants, antidepressants, opioid analgesics, and topical medications.

A Role for Global DNA Methylation Level and IL2 Expression in the Transition From Acute to Chronic Low Back Pain

Objectives: The transition from acute low back pain (aLBP) to chronic LBP (cLBP) results from a variety of factors, including epigenetic modifications of DNA. The aim of this study was to (1) compare global DNA (gDNA) methylation and histone acetylation at LBP onset between the aLBP and cLBP participants, (2) compare mRNA expression of genes with known roles in the transduction, maintenance, and/or modulation of pain between the aLBP and cLBP participants, (3) compare somatosensory function and pain ratings in our participants, and (4) determine if the aforementioned measurements were associated.

Methods: A total of 220 participants were recruited for this prospective observational study following recent onset of an episode of LBP. We retained 45 individuals whose gDNA was of sufficient quality for analysis. The final sample included 14 participants whose pain resolved within 6 weeks of onset (aLBP),15 participants that reported pain for 6 months (cLBP), and 16 healthy controls. Participants were subjected to quantitative sensory testing (QST), blood was drawn via venipuncture, gDNA isolated, and global DNA methylation and histone acetylation, as well as mRNA expression of 84 candidate genes, were measured.

Results: Individuals that develop cLBP display multimodal somatosensory hypersensitivity relative to aLBP participants. cLBP participants also had significantly lower global DNA methylation, which was negatively correlated with interleukin-2 (IL2) mRNA expression.

Discussion: cLBP is characterized by somatosensory hypersensitivity, lower global DNA methylation, and higher IL2 expression level compared to those whose pain will resolve quickly (aLBP). These results suggest potential diagnostic and therapeutic relevance for global DNA methylation and IL2 expression in the pathology underlying the transition from acute to chronic LBP.

Contribution of COMT and BDNF Genotype and Expression to the Risk of Transition From Acute to Chronic Low Back Pain

OBJECTIVES

A number of factors, including heritability and the environment, contribute to risk of transition from acute low back pain to chronic low back pain (CLBP). The aim of this study was to (1) compare somatosensory function and pain ratings at low back pain (LBP) onset between the acute low back pain and CLBP conditions and (2) evaluate associations between BDNF and COMT polymorphisms and expression levels at LBP onset to acute and chronic pain burden and risk for transition to the chronic pain state.

METHODS

In this longitudinal study, 220 participants were enrolled following recent onset of LBP and data were collected until the LBP resolved or until the end of the study at 6 months. Forty-two participants' pain resolved before 6 weeks from onset and 42 participants continued to have pain at 6 months. Patient-reported pain burden, somatosensory function (quantitative sensory testing), and blood samples were collected at each study visit.

RESULTS

CLBP is associated with greater pain burden and somatosensory hypersensitivity at the time of LBP onset. COMT rs4680 genotype (GG) was associated with acute cold pain sensitivity and with the risk for transition to CLBP while COMT expression was independently associated with risk for transition.

DISCUSSION

CLBP was characterized by higher reported pain burden and augmented hypersensitivity at LBP onset. COMT expression and genotype were associated with acute pain burden and likelihood of transition to CLBP.

Psychophysical evaluation of somatosensory function in oro-facial pain: achievements and challenges

AIM

This critical review describes key methodological aspects for a successful oro-facial psychophysical evaluation of the somatosensory system and highlights the diagnostic value of somatosensory assessment and management perspectives based on somatosensory profiling.

METHODS

This topical review was based on a non-systematic search for studies about somatosensory evaluation in oro-facial pain in PubMed and Embase.

RESULTS

The recent progress regarding the psychophysical evaluation of somatosensory function was largely possible due to the development and application of valid, reliable and standardised psychophysical methods. Qualitative sensory testing may be useful as a screening tool to rule out relevant somatosensory abnormalities. Nevertheless, the patient should preferably be referred to a more comprehensive assessment with the quantitative sensory testing battery if confirmation of somatosensory abnormalities is necessary. Moreover, the identification of relevant somatosensory alterations in chronic pain disorders that do not fulfil the current criteria to be regarded as neuropathic has also increased the usefulness of somatosensory evaluation as a feasible method to better characterise the patients and perhaps elucidate some underpinnings of the so-called 'nociplastic' pain disorders. Finally, an additional benefit of oro-facial pain treatment based on somatosensory profiling still needs to be demonstrated and convincing evidence of somatosensory findings as predictors of treatment efficacy in chronic oro-facial pain awaits further studies.

CONCLUSION

Psychophysical evaluation of somatosensory function in oro-facial pain is still in its infancy but with a clear potential to continue to improve the assessment, diagnosis and management of oro-facial pain patients.

Bedside testing for precision pain medicine

PURPOSE OF REVIEW

In recent years, the identification of therapy responders has become an increasing focus of pain research. On the basis of laboratory quantitative sensory testing, subgroups of patients were identified, which have been shown to predict treatment response. However, the high cost and time expenditure limits the use of these lab-QST protocols in clinical practice and large clinical trials.

RECENT FINDINGS

Recently, different bedside testing protocols were developed as easy-to-use alternative for lab-QST. In addition, patients can be subgrouped based on their symptoms by use of patient-reported outcome measures. First results suggest that these approaches can be used to stratify patients into pathophysiological-plausible subgroups predictive for treatment response.

SUMMARY

This review presents recently developed bedside approaches that can be implemented as stratification tools in future clinical trials to realize individualized pain medicine. Being complementary rather than replaceable, future studies should combine questionnaires and sensory testing and apply them prospectively in large clinical trials.

Profiling thermal pain using quantitative sensory testing in patients with trigeminal nerve injury

OBJECTIVES

To investigate the thermal pain phenotypes using QST in patients with unilateral trigeminal nerve injury and to explore whether these different thermal pain phenotypes are associated with clinical and psychophysical characteristics.

METHODS

This retrospective study included 84 patients diagnosed with posttraumatic trigeminal neuropathy involving inferior alveolar nerve (IAN) and lingual nerve (LN). Data on clinical characteristics, subjective symptoms including hypoesthesia, dysesthesia, and allodynia, and objective signs using thermal QST were collected and explored.

RESULTS

Three heat (heat hypoalgesia, heat hyperalgesia, and within normal range) and cold pain phenotypes (cold hypoalgesia, cold hyperalgesia, and within normal ranges) were identified, respectively. Thermal hypoalgesia was more frequently observed than thermal hyperalgesia. Heat hypoalgesia regardless of cold pain abnormalities appears to be associated with subjective negative symptoms, while thermal hyperalgesia seems to have little relationship with negative and positive symptoms. Thermal pain phenotypes were associated with loss of innocuous thermal sensation. Unlike heat pain phenotypes, cold pain phenotypes differed between IAN injury and LN injury.

CONCLUSION

The thermal pain phenotypes identified in this study seem to be related to clinical and psychophysical findings differently. These results would be a good starting point for assessing posttraumatic trigeminal neuropathy and interpreting the thermal QST results.

Neuropathic Pain: From Mechanisms to Treatment

Neuropathic pain caused by a lesion or disease of the somatosensory nervous system is a common chronic pain condition with major impact on quality of life. Examples include trigeminal neuralgia, painful polyneuropathy, postherpetic neuralgia, and central poststroke pain. Most patients complain of an ongoing or intermittent spontaneous pain of, for example, burning, pricking, squeezing quality, which may be accompanied by evoked pain, particular to light touch and cold. Ectopic activity in, for example, nerve-end neuroma, compressed nerves or nerve roots, dorsal root ganglia, and the thalamus may in different conditions underlie the spontaneous pain. Evoked pain may spread to neighboring areas, and the underlying pathophysiology involves peripheral and central sensitization. Maladaptive structural changes and a number of cell-cell interactions and molecular signaling underlie the sensitization of nociceptive pathways. These include alteration in ion channels, activation of immune cells, glial-derived mediators, and epigenetic regulation. The major classes of therapeutics include drugs acting on α₂δ subunits of calcium channels, sodium channels, and descending modulatory inhibitory pathways.

A systematic review on diagnostic test accuracy of magnetic resonance neurography versus clinical neurosensory assessment for post-traumatic trigeminal neuropathy in patients reporting neurosensory disturbance

OBJECTIVES

To perform a systematic review of published studies on diagnostic accuracy of magnetic resonance neurography (MRN) vs clinical neurosensory testing (NST) for post-traumatic trigeminal neuropathy (PTTN) in patients reporting neurosensory disturbances (NSD).

METHODS

Human studies except case reports, reviews, systematic reviews and meta-analyses were included. PubMed, Embase, Web of Science and Cochrane Library were consulted. Risk of bias assessment was conducted using the Quality Assessment of Diagnostic Accuracy Studies 2 tool. Predetermined data extraction parameters were noted and summarized.

RESULTS

8 studies met eligibility criteria of which 7 were retrospective, representing 444 subjects. Most studies were at high risk of bias with low applicability concerns. Populations and objectives were divergent with a large variation in timing (3 days-17 years post injury) and parameters (multiple coil designs, fat suppression techniques, additional contrast agent) of MRI acquisition. T₂ weighted 3 T imaging with short echo times (2.2-100 ms) and fat suppression was applied in seven studies, techniques varied. Determination of sensitivity and specificity could not be performed due to the methodological variation between studies and lacking comparative data between index and reference tests. Based on limited data, PTTN correlated reasonably well between clinical assessment, intraoperative findings and MRN abnormalities (k = 0.57). Increased signal intensity correlated with persistency of neurosensory disturbances in one study. Intra- (ICC 0.914-0.927) and interobserver (k = 0.70-0.891) MRN variability was considered good to excellent. One retrospective study showed substantial impact of MRN on clinical decision making in one-third of patients.

CONCLUSION

Currently, there is insufficient scientific knowledge to support or refute the use of MRN. Based on limited data, MRN seems promising and reliable in detection and grading of PTTN. Methodological issues underline the importance for prospective blinded studies with standardization of signal intensity calculation and rigorous reporting of MRI acquisition parameters.

Chemotherapy-induced peripheral neuropathy: where are we now?

Chemotherapy-induced peripheral neuropathy (CIPN) is a major challenge, with increasing impact as oncological treatments, using potentially neurotoxic chemotherapy, improve cancer cure and survival. Acute CIPN occurs during chemotherapy, sometimes requiring dose reduction or cessation, impacting on survival. Around 30% of patients will still have CIPN a year, or more, after finishing chemotherapy. Accurate assessment is essential to improve knowledge around prevalence and incidence of CIPN. Consensus is needed to standardize assessment and diagnosis, with use of well-validated tools, such as the EORTC-CIPN 20. Detailed phenotyping of the clinical syndrome moves toward a precision medicine approach, to individualize treatment. Understanding significant risk factors and pre-existing vulnerability may be used to improve strategies for CIPN prevention, or to use targeted treatment for established CIPN. No preventive therapies have shown significant clinical efficacy, although there are promising novel agents such as histone deacetylase 6 (HDAC6) inhibitors, currently in early phase clinical trials for cancer treatment. Drug repurposing, eg, metformin, may offer an alternative therapeutic avenue. Established treatment for painful CIPN is limited. Following recommendations for general neuropathic pain is logical, but evidence for agents such as gabapentinoids and amitriptyline is weak. The only agent currently recommended by the American Society of Clinical Oncology is duloxetine. Mechanisms are complex with changes in ion channels (sodium, potassium, and calcium), transient receptor potential channels, mitochondrial dysfunction, and immune cell interactions. Improved understanding is essential to advance CIPN management. On a positive note, there are many potential sites for modulation, with novel analgesic approaches.

New Perspective in Diabetic Neuropathy: From the Periphery to the Brain, a Call for Early Detection, and Precision Medicine

Diabetic peripheral neuropathy (DPN) is a common chronic complication of diabetes mellitus. It leads to distressing and expensive clinical sequelae such as foot ulceration, leg amputation, and neuropathic pain (painful-DPN). Unfortunately, DPN is often diagnosed late when irreversible nerve injury has occurred and its first presentation may be with a diabetic foot ulcer. Several novel diagnostic techniques are available which may supplement clinical assessment and aid the early detection of DPN. Moreover, treatments for DPN and painful-DPN are limited. Only tight glucose control in type 1 diabetes has robust evidence in reducing the risk of developing DPN. However, neither glucose control nor pathogenetic treatments are effective in painful-DPN and symptomatic treatments are often inadequate. It has recently been hypothesized that using various patient characteristics it may be possible to stratify individuals and assign them targeted therapies to produce better pain relief. We review the diagnostic techniques which may aid the early detection of DPN in the clinical and research environment, and recent advances in precision medicine techniques for the treatment of painful-DPN.

Developing Modern Pain Therapies

Chronic pain afflicts as much as 50% of the population at any given time but our methods to address pain remain limited, ineffective and addictive. In order to develop new therapies an understanding of the mechanisms of painful sensitization is essential. We discuss here recent progress in the understanding of mechanisms underlying pain, and how these mechanisms are being targeted to produce modern, specific therapies for pain. Finally, we make recommendations for the next generation of targeted, effective, and safe pain therapies.

Biological predictors of chemotherapy-induced peripheral neuropathy (CIPN): MASCC neurological complications working group overview

Chemotherapy-induced peripheral neuropathy (CIPN) is a common and debilitating condition associated with a number of chemotherapeutic agents. Drugs commonly implicated in the development of CIPN include platinum agents, taxanes, vinca alkaloids, bortezomib, and thalidomide analogues. As a drug response can vary between individuals, it is hypothesized that an individual's specific genetic variants could impact the regulation of genes involved in drug pharmacokinetics, ion channel functioning, neurotoxicity, and DNA repair, which in turn affect CIPN development and severity. Variations of other molecular markers may also affect the incidence and severity of CIPN. Hence, the objective of this review was to summarize the known biological (molecular and genomic) predictors of CIPN and discuss the means to facilitate progress in this field.

Risks of harm with cannabinoids, cannabis, and cannabis-based medicine for pain management relevant to patients receiving pain treatment: protocol for an overview of systematic reviews

Supplemental Digital Content is Available in the Text.

Introduction:

With the increasing availability of cannabis and cannabinoids and their potential utility for pain treatment, there is a growing need to evaluate the risk-benefit considerations of cannabinoids for the management of pain. As part of the IASP Cannabis and Cannabinoids Task Force, this protocol describes a planned overview of systematic reviews summarizing the risks of harm with cannabinoids that are relevant to patients receiving pain treatment.

Methods:

This overview will involve literature searches of several databases and a defined search strategy that will target systematic reviews or meta-analyses of cannabinoids where harms are the primary focus. Data extraction will include various features of the cannabinoid(s) and the harm(s) being studied as well as other methodological features of each included systematic review. Methodological quality of each included review will be assessed using AMSTAR-2 as well as compliance with the PRISMA harms checklist. Prospero registration pending.

Discussion:

The broad overview of reviews defined by this protocol is expected to synthesize available good quality evidence of harms that will help inform risk-benefit considerations about the use of cannabinoids for pain management.

The Novel Activity of Carbamazepine as an Activation Modulator Extends from NaV1.7 Mutations to the NaV1.8-S242T Mutant Channel from a Patient with Painful Diabetic Neuropathy

Neuropathic pain in patients carrying sodium channel gain-of-function mutations is generally refractory to pharmacotherapy. However, we have shown that pretreatment of cells with clinically achievable concentration of carbamazepine (CBZ; 30 μM) depolarizes the voltage dependence of activation in some NaV1.7 mutations such as S241T, a novel CBZ mode of action of this drug. CBZ reduces the excitability of dorsal root ganglion (DRG) neurons expressing NaV1.7-S241T mutant channels, and individuals carrying the S241T mutation respond to treatment with CBZ. Whether the novel activation-modulating activity of CBZ is specific to NaV1.7, and whether this pharmacogenomic approach can be extended to other sodium channel subtypes, are not known. We report here the novel NaV1.8-S242T mutation, which corresponds to the NaV1.7-S241T mutation, in a patient with neuropathic pain and diabetic peripheral neuropathy. Voltage-clamp recordings demonstrated hyperpolarized and accelerated activation of NaV1.8-S242T. Current-clamp recordings showed that NaV1.8-S242T channels render DRG neurons hyperexcitable. Structural modeling shows that despite a substantial difference in the primary amino acid sequence of NaV1.7 and NaV1.8, the S242 (NaV1.8) and S241 (NaV1.7) residues have similar position and orientation in the domain I S4-S5 linker of the channel. Pretreatment with a clinically achievable concentration of CBZ corrected the voltage dependence of activation of NaV1.8-S242T channels and reduced DRG neuron excitability as predicted from our pharmacogenomic model. These findings extend the novel activation modulation mode of action of CBZ to a second sodium channel subtype, NaV1.8.