A cross-sectional cohort survey in 2100 patients with painful diabetic neuropathy and postherpetic neuralgia: Differences in demographic data and sensory symptoms

From Mechanism to Cure: Renewing the Goal to Eliminate the Disease of Pain

Objective

Persistent pain causes untold misery worldwide and is a leading cause of disability. Despite its astonishing prevalence, pain is undertreated, at least in part because existing therapeutics are ineffective or cause intolerable side effects. In this review, we cover new findings about the neurobiology of pain and argue that all but the most transient forms of pain needed to avoid tissue damage should be approached as a disease where a cure can be the goal of all treatment plans, even if attaining this goal is not yet always possible.

Design

We reviewed the literature to highlight recent advances in the area of the neurobiology of pain.

Results

We discuss barriers that are currently hindering the achievement of this goal, as well as the development of new therapeutic strategies. We also discuss innovations in the field that are creating new opportunities to treat and even reverse persistent pain, some of which are in late-phase clinical trials.

Conclusion

We conclude that the confluence of new basic science discoveries and development of new technologies are creating a path toward pain therapeutics that should offer significant hope of a cure for patients and practitioners alike. Classification of Evidence. Our review points to new areas of inquiry for the pain field to advance the goal of developing new therapeutics to treat chronic pain.

painPREDICT: first interim data from the development of a new patient-reported pain questionnaire to predict treatment response using sensory symptom profiles

Objective: Sensory symptom patterns may be useful for predicting treatment response, and, thus, improve individual therapy in patients suffering from neuropathic pain (NeP). Existing screening questionnaires focus predominately on neuropathic mechanisms without consideration of nociceptive mechanisms or mixed pain states. This study aimed to develop a new questionnaire, painPREDICT, using a wide set of patient-reported descriptors potentially associated with neuropathic and nociceptive pain mechanisms, and to explore sensory symptom patterns. Methods: PainPREDICT was constructed based on exploratory (n = 27 patients) and cognitive debriefing interviews (n = 49 patients and nine physicians), across five NeP conditions. The pilot questionnaire was then administered in a non-interventional, cross-sectional, multi-center study to 840 pain patients across the US and Germany. The identification of a sensory symptom pattern was based on hybrid clustering resulting from items standardization followed by principal component analysis. Results: The final questionnaire included 20 items covering: pain intensity, location of pain, course of pain, and sensory symptoms. Most patients participating in the cross-sectional study suffered either from painful diabetic polyneuropathy (n = 330) or radiculopathy (n = 349), fewer from central pain (n = 61) or other types of NeP (n = 100). The hybrid clustering of the new questionnaire data identified three different characteristic sensory symptom profiles in patients with NeP: "Irritable nociceptors", "deafferentation pain", and "pain attacks with nociceptive component". Although some differences in the distribution of the sensory profiles were found, all profiles were represented in all NeP etiology groups. Conclusions: This study set the ground of painPREDICT and showed promising results for its use to categorize patients according to sensory symptom patterns.

Somatosensory profiles in acute herpes zoster and predictors of postherpetic neuralgia

This prospective cohort study aimed to characterize the sensory profile during acute herpes zoster (AHZ) and to explore sensory signs as well as physical and psychosocial health as predictors for postherpetic neuralgia (PHN). Results of quantitative sensory testing of 74 patients with AHZ at the affected site and at the distant contralateral control site were compared to a healthy control group. Pain characteristics (Neuropathic Pain and Symptom Inventory and SES), physical functioning, and psychosocial health aspects (Pain Disability Index, SF-36, and STAI) were assessed by questionnaires. Patients with PHN (n = 13) at 6-month follow-up were compared to those without PHN (n = 45). Sensory signs at the affected site were thermal and vibratory hypesthesia, dynamic mechanical allodynia (DMA), pressure hyperalgesia, and high wind-up (18%-29%), as well as paradoxical heat sensations and pinprick hypalgesia (13.5%). The unaffected control site exhibited thermal and vibratory hypesthesia, DMA, and pressure hyperalgesia. Dynamic mechanical allodynia and pinprick hypalgesia were mutually exclusive. Postherpetic neuralgia was associated with DMA (38.5% vs 6.7%; P = 0.010) and vibratory hypesthesia (38.5% vs 11.1%; P = 0.036) at the control site, with mechanical gain and/or loss combined with normal thermal detection (affected site: 69.2% vs 31.1%; P = 0.023; control site: 53.8% vs 15.5%; P = 0.009). Pain Disability Index (P = 0.036) and SES affective pain perception scores (P = 0.031) were over 50% higher, and 6 of 8 SF-36 subscores were over 50% lower (P < 0.045) in PHN. Sensory profiles in AHZ indicate deafferentation and central but not peripheral sensitization. Sensory signs at distant body sites, strong affective pain perception, as well as reduced quality of life and physical functioning in the acute phase may reflect risk factors for the transition to PHN.

Exaggerated mechanoreflex in early-stage type 1 diabetic rats: role of Piezo channels

Recent findings have shown that muscle contraction evokes an exaggerated pressor response in type 1 diabetes mellitus (T1DM) rats; however, it is not known whether the mechanoreflex, which is commonly stimulated by stretching the Achilles tendon, contributes to this abnormal response. Furthermore, the role of mechano-gated Piezo channels, found on thin-fiber afferent endings, in evoking the mechanoreflex in T1DM is also unknown. Therefore, in male and female streptozotocin (STZ, 50 mg/kg)-induced T1DM and healthy control (CTL) rats, we examined the pressor and cardioaccelerator responses to tendon stretch during the early stage of the disease. To determine the role of Piezo channels, GsMTx-4, a selective Piezo channel inhibitor, was injected into the arterial supply of the hindlimb. At 1 wk after STZ injection in unanesthetized, decerebrate rats, we stretched the Achilles tendon for 30 s and measured pressor and cardioaccelerator responses. We then compared pressor and cardioaccelerator responses to tendon stretch before and after GsMTx-4 injection (10 µg/100 ml). We found that the pressor (change in mean arterial pressure) response [41 ± 5 mmHg ( n = 15) for STZ and 18 ± 3 mmHg ( n = 11) for CTL ( P < 0.01)] and cardioaccelerator (change in heart rate) response [18 ± 4 beats/min for STZ ( n = 15) and 8 ± 2 beats/min ( n = 11) for CTL ( P < 0.05)] to tendon stretch were exaggerated in STZ rats. Local injection of GsMTx-4 attenuated the pressor [55 ± 7 mmHg ( n = 6) before and 27 ± 9 mmHg ( n = 6) after GsMTx-4 ( P < 0.01)], but not the cardioaccelerator, response to tendon stretch in STZ rats and had no effect on either response in CTL rats. These data suggest that T1DM exaggerates the mechanoreflex response to tendon stretch and that Piezo channels play a role in this exaggeration.

Quantitative sensory testing response patterns to capsaicin- and ultraviolet-B-induced local skin hypersensitization in healthy subjects: a machine-learned analysis

The comprehensive assessment of pain-related human phenotypes requires combinations of nociceptive measures that produce complex high-dimensional data, posing challenges to bioinformatic analysis. In this study, we assessed established experimental models of heat hyperalgesia of the skin, consisting of local ultraviolet-B (UV-B) irradiation or capsaicin application, in 82 healthy subjects using a variety of noxious stimuli. We extended the original heat stimulation by applying cold and mechanical stimuli and assessing the hypersensitization effects with a clinically established quantitative sensory testing (QST) battery (German Research Network on Neuropathic Pain). This study provided a 246 × 10-sized data matrix (82 subjects assessed at baseline, following UV-B application, and following capsaicin application) with respect to 10 QST parameters, which we analyzed using machine-learning techniques. We observed statistically significant effects of the hypersensitization treatments in 9 different QST parameters. Supervised machine-learned analysis implemented as random forests followed by ABC analysis pointed to heat pain thresholds as the most relevantly affected QST parameter. However, decision tree analysis indicated that UV-B additionally modulated sensitivity to cold. Unsupervised machine-learning techniques, implemented as emergent self-organizing maps, hinted at subgroups responding to topical application of capsaicin. The distinction among subgroups was based on sensitivity to pressure pain, which could be attributed to sex differences, with women being more sensitive than men. Thus, while UV-B and capsaicin share a major component of heat pain sensitization, they differ in their effects on QST parameter patterns in healthy subjects, suggesting a lack of redundancy between these models.

Inflammatory Macrophages in the Sciatic Nerves Facilitate Neuropathic Pain Associated with Type 2 Diabetes Mellitus

Despite the requirement for effective medication against neuropathic pain associated with type 2 diabetes mellitus (T2DM), mechanism-based pharmacotherapy has yet to be established. Given that long-lasting neuroinflammation, driven by inflammatory macrophages in the peripheral nerves, plays a pivotal role in intractable pain, it is important to determine whether inflammatory macrophages contribute to neuropathic pain associated with T2DM. To generate an experimental model of T2DM, C57BL/6J mice were fed a high-fat diet (HFD) ad libitum. Compared with control diet feeding, obesity and hyperglycemia were observed after HFD feeding, and the mechanical pain threshold evaluated using the von Frey test was found to be decreased, indicating the development of mechanical allodynia. The expression of mRNA markers for macrophages, inflammatory cytokines, and chemokines were significantly upregulated in the sciatic nerve (SCN) after HFD feeding. Perineural administration of saporin-conjugated anti-Mac1 antibody (Mac1-Sap) improved HFD-induced mechanical allodynia. Moreover, treatment of Mac1-Sap decreased the accumulation of F4/80+ macrophages and the upregulation of inflammatory mediators in the SCN after HFD feeding. Inoculation of lipopolysaccharide-activated peritoneal macrophages in tissue surrounding the SCN elicited mechanical allodynia. Furthermore, pharmacological inhibition of inflammatory macrophages by either perineural or systemic administration of TC-2559 [4-(5-ethoxy-3-pyridinyl)-N-methyl-(3E)-3-buten-1-amine difumarate], a α4β2 nicotinic acetylcholine receptor-selective agonist, relieved HFD-induced mechanical allodynia. Taken together, inflammatory macrophages that accumulate in the SCN mediate the pathophysiology of neuropathic pain associated with T2DM. Inhibitory agents for macrophage-driven neuroinflammation could be potential candidates for novel pharmacotherapy against intractable neuropathic pain.

Stratification of neuropathic pain patients: the road to mechanism-based therapy?

PURPOSE OF REVIEW

It has been demonstrated that within one pain entity, patients may report highly heterogenic sensory signs and symptoms. Although mechanism might differ fundamentally between those patients, yet the treatment recommendations are uniform throughout all phenotypes. Therefore, the introduction of new stratification tools could pave the way to an individualized pain treatment.

RECENT FINDINGS

In the past, retrospective stratifications of patients successfully identified responders to certain pharmacological treatments. This indicated predictive validity and reliability of this classification tool in those patient subgroups. Further on, these observations have been confirmed in prospective studies.

SUMMARY

This review focusses on recent achievements in neuropathic pain and suggests a promising implementation of an individualized pharmacological therapy in the future.

Sensory profiles are comparable in patients with distal and proximal entrapment neuropathies, while the pain experience differs

OBJECTIVE

Distal and proximal entrapment neuropathies such as carpal tunnel syndrome (CTS) and cervical radiculopathy (CR) share similar etiologies. Experimental models suggest that, despite comparable etiology, pathomechanisms associated with injuries of the peripheral and central axon branches are distinct. This study therefore compared self-reported and elicited sensory profiles in patients with distal and proximal entrapment neuropathies.

METHODS

Patients with electrodiagnostically confirmed CTS (n = 103) and patients with CR (n = 23) were included in this study. A group of healthy participants served as controls (n = 39). Symptoms and sensory profiles were evaluated using quantitative sensory testing (QST) and a self-reported neuropathic pain questionnaire (painDETECT).

RESULTS

Both patient groups were characterized by a loss of function in thermal and mechanical detection in the main pain area and dermatome compared to healthy reference data (p < .001). There was no significant difference between patients with CTS and CR in pain and detection thresholds except for reduced vibration sense in the main pain area (p < .001) and reduced pressure pain sensitivity in the dermatome in patients with CR (p < .001). However, patients with CR reported higher pain intensities (p = .008), more severe pain attacks (p = .009) and evoked pain by light pressure (p = .002) compared to patients with CTS.

CONCLUSION

While QST profiles were similar between patients with CTS and CR, self-reported pain profiles differed and may suggest distinct underlying mechanisms in these patient cohorts.

Impaired Nociception in the Diabetic Ins2+/Akita Mouse

The mechanisms responsible for painful and insensate diabetic neuropathy are not completely understood. Here, we have investigated sensory neuropathy in the Ins2^+/Akita mouse, a hereditary model of diabetes. Akita mice become diabetic soon after weaning, and we show that this is accompanied by an impaired mechanical and thermal nociception and a significant loss of intraepidermal nerve fibers. Electrophysiological investigations of skin-nerve preparations identified a reduced rate of action potential discharge in Ins2^+/Akita mechanonociceptors compared with wild-type littermates, whereas the function of low-threshold A-fibers was essentially intact. Studies of isolated sensory neurons demonstrated a markedly reduced heat responsiveness in Ins2^+/Akita dorsal root ganglion (DRG) neurons, but a mostly unchanged function of cold-sensitive neurons. Restoration of normal glucose control by islet transplantation produced a rapid recovery of nociception, which occurred before normoglycemia had been achieved. Islet transplantation also restored Ins2^+/Akita intraepidermal nerve fiber density to the same level as wild-type mice, indicating that restored insulin production can reverse both sensory and anatomical abnormalities of diabetic neuropathy in mice. The reduced rate of action potential discharge in nociceptive fibers and the impaired heat responsiveness of Ins2^+/Akita DRG neurons suggest that ionic sensory transduction and transmission mechanisms are modified by diabetes.

A pain in the skin. Regenerating nerve sprouts are distinctly associated with ongoing burning pain in patients with diabetes

BACKGROUNDS

Patients with diabetic polyneuropathy commonly suffer from ongoing burning pain and dynamic mechanical allodynia. In this clinical and skin biopsy study, we aimed at assessing how intraepidermal regenerating nerve sprouts are associated with these two types of pain.

METHODS

We consecutively enrolled 85 patients with diabetic polyneuropathy. All patients underwent skin biopsy at the distal leg. Intraepidermal nerve fibres were immunostained with the anti-protein gene product 9.5 (PGP9.5) to quantify all intraepidermal nerve fibres, and the growth-associated protein 43 (GAP43) to quantify regenerating nerve sprouts.

RESULTS

We found that the GAP43-stained intraepidermal nerve fibre density and the ratio GAP43/PGP9.5 were significantly higher in patients with ongoing burning pain than in those without. The area of receiver operating characteristic (ROC) curve for the ratio GAP43/PGP9.5 was 0.74 and yielded a sensitivity and specificity for identifying ongoing burning pain of 72% and 71%, respectively. Conversely, although the density of PGP9.5 and GAP43 intraepidermal nerve fibre was higher in patients with dynamic mechanical allodynia than in those without, this difference was statistically weak and the ROC curve analysis of skin biopsy variables for this type of pain failed to reach the statistical significance.

CONCLUSION

Our clinical and skin biopsy study showed that ongoing burning pain was strongly associated with regenerating sprouts, as assessed with GAP43 immunostaining. This finding improves our understanding on the mechanisms underlying neuropathic pain in patients with diabetic polyneuropathy and suggests that the GAP43/PGP 9.5 ratio might be used as an objective marker for ongoing burning pain due to regenerating sprouts.

SIGNIFICANCE

Our skin biopsy study showing that regenerating sprouts, as assessed with GAP43-staining, were strongly associated with ongoing burning pain, improves our knowledge on the mechanisms underlying neuropathic pain in patients with diabetes.

Neuropathic pain after sarcoma surgery: Prevalence and predisposing factors

Surgery for sarcoma frequently causes nerve damage as the dissection often violates the internervous plane. Nerve damage may cause neuropathic pain (NP), which can result in persistent pain after surgery. This is the first study to investigate the prevalence and associated factors of postoperative NP in patients who underwent surgery for sarcoma of the extremities or pelvis.Patients (n = 144) who underwent curative surgery at least 6 months prior to the visit for histologically confirmed sarcoma were enrolled. The presence of NP was assessed by administering PainDetect, a widely used questionnaire for detecting NP. Patients with PainDetect scores ≥13 were considered to have NP. The possible factors that might be associated with the development of NP were investigated: patient characteristics, tumor characteristics, extent of surgery, and adjuvant therapy.Out of 144 patients, 36 patients (25%) had NP. Patients with NP had significantly worse visual analog scale score (P < .001), Toronto Extremity Salvage Score (P < .001), and Musculoskeletal Tumor Society Rating Scale score (P < .001) than patients without NP. Among the possible factors associated with NP, patients with NP were more likely to have undergone pelvic surgery (P = .002) and multiple surgeries (P = .014) than patients without NP. In logistic regression analysis, pelvic surgery (odds ratio = 5.05, P = .005) and multiple surgeries (odds ratio = 2.33, P = .038) were independent factors associated with NP after sarcoma surgery.This study suggests that the prevalence of NP after surgery for sarcoma is considerable. Surgery of the pelvis and multiple surgeries are predictive of postoperative persistent NP.

Reducing CXCR4-mediated nociceptor hyperexcitability reverses painful diabetic neuropathy

Painful diabetic neuropathy (PDN) is an intractable complication of diabetes that affects 25% of patients. PDN is characterized by neuropathic pain and small-fiber degeneration, accompanied by dorsal root ganglion (DRG) nociceptor hyperexcitability and loss of their axons within the skin. The molecular mechanisms underlying DRG nociceptor hyperexcitability and small-fiber degeneration in PDN are unknown. We hypothesize that chemokine CXCL12/CXCR4 signaling is central to this mechanism, as we have shown that CXCL12/CXCR4 signaling is necessary for the development of mechanical allodynia, a pain hypersensitivity behavior common in PDN. Focusing on DRG neurons expressing the sodium channel Nav1.8, we applied transgenic, electrophysiological, imaging, and chemogenetic techniques to test this hypothesis. In the high-fat diet mouse model of PDN, we were able to prevent and reverse mechanical allodynia and small-fiber degeneration by limiting CXCR4 signaling or neuronal excitability. This study reveals that excitatory CXCR4/CXCL12 signaling in Nav1.8-positive DRG neurons plays a critical role in the pathogenesis of mechanical allodynia and small-fiber degeneration in a mouse model of PDN. Hence, we propose that targeting CXCR4-mediated DRG nociceptor hyperexcitability is a promising therapeutic approach for disease-modifying treatments for this currently intractable and widespread affliction.

Sensory Symptom Profiles of Patients With Neuropathic Pain After Spinal Cord Injury

AIM

Individuals experiencing neuropathic pain (NP) after spinal cord injury (SCI) present with a variety of pain descriptors in different combinations and at different intensities. These sensory features form distinct patterns, known as sensory symptom profiles.

METHODS

In the present cross-sectional study, we have used a multivariate statistical method (multiple correspondence analysis) to categorize the sensory symptom profiles of a cohort of 338 patients with at-level or below-level NP after SCI. We also investigated possible associations between positive neuropathic symptoms and features of the neurological lesion.

RESULTS

The majority of participants had a combination of pain descriptors, with 59% presenting with 3 or 4 pain subtypes. No significant associations were found between specific pain profiles and etiology or clinical degree of the neurological lesion. Furthermore, similar symptom profiles were seen in patients with at-level and below-level NP. The most frequent pattern observed in patients with cervical SCI consisted predominantly of electric shocks and tingling, without burning, pressure pain, or allodynia.

CONCLUSIONS

Classification of SCI-NP patients into the 5 groups identified in the present study based on their distinct sensory symptom profiles may allow identification of those most likely to respond to a specific analgesic approach.

Clinical and Neurophysiological Features of Leprosy Patients with Neuropathic Pain

Neural pain is a frequent symptom in leprosy disease. There is a paucity of data regarding neural pain diagnostics resulting in common prescriptive errors when neuritis is confused with neuropathic or mixed nociceptive-neuropathic pain. The present study identified important demographic, clinical, and neurophysiological features of 42 leprosy neuropathy patients presenting neuropathic pain (NP). During routine evaluations, patients were selected asking if they had ever experienced neural pain. Data analyses of their pain characteristics, clinical examination results, and both the Douleur Neuropathique 4 Questionnaire and Hamilton Depression Scale scores were used to classify these patients. The most common word they used to describe the sensation of pain for 25 (60%) of these patients was "burning." In the early stages of the disease and before leprosy diagnosis, 19 (45%) had already complained about NP and leprosy treatment was unable to prevent its occurrence in 15 (36%). Leprosy reactions, considered NP risk factors, occurred in 32 (76%) cases. Knowledge of typical NP characteristics could be used to develop more effective therapeutic approaches for a notoriously difficult-to-treat pain condition.

Comparison of 2 methods of neuropathic pain assessment in carpal tunnel syndrome and hand functions

OBJECTIVE

To compare the effectiveness of the Leeds Assessment of Neuropathic Symptoms and Signs Scale (LANSS) to the painDETECT questionnaire (PD-Q) in Carpal Tunnel Syndrome (CTS), and determine if there are any differences between hand related functions in the 2 questionnaires.

METHODS

This prospective clinical trial was conducted from April to July 2014. Ninety patients with a positive Tinel or Phalen sign were recruited. Hands were evaluated by electromyography and grouped according to mild, moderate or severe involvement. Neuropathic pain was analysed by the LANSS and the PD-Q; hand functions were evaluated by the Duruoz Hand Index (DHI), Semmes Weinstein monofilaments and grip strength.

RESULTS

Electromyographic findings revealed 32.9% of hands had mild, 61.8% had moderate and 5.3% had severe CTS. There was a correlation between the LANSS scores and the Visual Analogue Scale (VAS) pain, while the PD-Q scores were correlated with the VAS pain, DHI and Semmes Weinstein Monofilaments (SWM). Comparison of the hand related parameters of the questionnaires showed there was a statistically significant difference between the 2 groups with respect to the DHI and SWM tests in the PD-Q. However, there was no difference in the LANSS.

CONCLUSION

Although there was a significant correlation between the LANSS and PD-Q scores, the PD-Q scores revealed better correlation coefficients in VAS pain, DHI scores and SWM tests. In conclusion, the PD-Q seems to be better than the LANSS both in neuropathic pain and in detecting functions related to hand abilities.

Corneal confocal microscopy as a non-invasive test to assess diabetic peripheral neuropathy

OBJECTIVE

To evaluate the efficacy of corneal confocal microscopy (CCM) as a non-invasive test to assess diabetic peripheral neuropathy in Chinese patients diagnosed with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Diabetic distal symmetric polyneuropathy (DSPN) and its severity degrees were assessed based on the modified Toronto diagnostic criteria in 128 patients with type 2 diabetes (No DSPN [n = 49], mild DSPN [n = 43], moderate-to-severe DSPN [n = 36]) and 24 age-matched controls. CCM was also examined in all enrolled subjects. Corneal nerve fiber length (CNFL), corneal nerve branch density (CNBD) and corneal nerve fiber density (CNFD) were analyzed by Fiji imaging analysis software. The efficacy of CCM as a non-invasive test to assess diabetic peripheral neuropathy was determined.

RESULTS

CNFL was 17.99 ± 0.66, 15.82 ± 0.64, 14.98 ± 0.63, and 12.49 ± 0.93 in healthy controls, T2DM patients with no, mild, and moderate-to-severe DPN, respectively. CNFL in type 2 diabetes patients with no, mild, and moderate-to-severe DSPN demonstrated a significant reduction than in healthy controls (P = .012, .003 and <.001, respectively). CNFL in patients with moderate-to-severe DSPN was significantly shorter than in patients with no or mild DSPN (P < .001 and .004, respectively). CNBD was 41.48 ± 3.35, 33.02 ± 2.50, 30.91 ± 2.33, and 18.00 ± 2.33 in healthy controls, T2DM patients with no, mild, and moderate-to-severe DPN, respectively. CNBD in healthy control was significantly higher than in type 2 diabetes patients with no, mild, and moderate-to-severe DSPN (P = .036, 0.016 and < .001, respectively). CNBD in patients with moderate-to-severe DSPN was significantly lower than in patients with no or mild DSPN (P < .001 for both). CNFD was 35.32 ± 1.18, 35.68 ± 1.10, 34.54 ± 1.12, and 32.28 ± 1.76 in healthy controls, T2DM patients with no, mild, and moderate-to-severe DPN, respectively. CNFD did not differ among the four groups. In an analysis that divided CNFL, CNFD and CNBD into quartiles, there were no significant differences in electromyography findings and vibration perception threshold among the 4 groups; however, significant differences were seen in the positive distribution of temperature perception measurements following CNFL and CNBD stratification (P = .001 and < .001, respectively).

CONCLUSION

CCM might be a non-invasive method for detecting DSPN and its severity degree in Chinese patients diagnosed with type 2 diabetes.

The H-Reflex as a Biomarker for Spinal Disinhibition in Painful Diabetic Neuropathy

PURPOSE OF REVIEW

Neuropathic pain may arise from multiple mechanisms and locations. Efficacy of current treatments for painful diabetic neuropathy is limited to an unpredictable subset of patients, possibly reflecting diversity of pain generator mechanisms, and there is a lack of targeted treatments for individual patients. This review summarizes preclinical evidence supporting a role for spinal disinhibition in painful diabetic neuropathy, the physiology and pharmacology of rate-dependent depression (RDD) of the spinal H-reflex and the translational potential of using RDD as a biomarker of spinally mediated pain.

RECENT FINDINGS

Impaired RDD occurs in animal models of diabetes and was also detected in diabetic patients with painful vs painless neuropathy. RDD status can be determined using standard neurophysiological equipment. Loss of RDD may provide a clinical biomarker of spinal disinhibition, thereby enabling a personalized medicine approach to selection of current treatment options and enrichment of future clinical trial populations.

A review of Neuropathic Pain: From Guidelines to Clinical Practice

Neuropathic pain is a chronic condition representing a significant burden for patients, society, and healthcare systems. The prevalence of neuropathic pain in the general population has been estimated at 7–8% and is expected to increase in the future. Neuropathic pain differs from nociceptive pain and requires a different therapeutic approach; and the management of neuropathic pain is complicated and challenging. This chapter discusses clinical practice guidelines for neuropathic pain and their usefulness in clinical practice.

Funding: Pfizer, Italy.

A standardized clinical evaluation of phenotypic diversity in diabetic polyneuropathy

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

Quantification of small fiber pathology in patients with sarcoidosis and chronic pain using cornea confocal microscopy and skin biopsies

Small fiber pathology with concomitant chronic neuropathic pain is a common complication of sarcoidosis. The gold standard of diagnosis of small fiber neuropathy (SFN) is the quantification of small nerve fibers in skin biopsies in combination with patient history and psychophysical tests; a new technique is the quantification of small nerve fibers in the cornea using cornea confocal microscopy (CCM). Here, we studied small fiber morphology in sarcoidosis patients with neuropathic pain using skin biopsies, CCM, and quantitative sensory testing (QST). Our aim was to construct specific phenotypes of neuropathic pain in sarcoidosis. Fifty-eight patients with a confirmed diagnosis of sarcoidosis and with moderate-to-severe neuropathic pain were tested. Decreased intraepidermal nerve fiber density (IENFD) from skin biopsies was found in 28% of patients, and CCM abnormalities were observed in 45% of patients. There was no correlation between CCM and IENFD abnormalities. Eighty-three percent of patients had abnormal thermal detection thresholds, a sign of small fiber dysfunction. Based on the presence or absence of abnormalities in IENFD and CCM, four distinct phenotypes were identified with a distinct homogeneous pattern of somatosensory symptoms. We argue that these distinct phenotypes have a similar mechanistic construct with specific phenotype-specific treatment options. Additionally, our data suggest the presence of patients with length- and nonlength-dependent SFN within this population of sarcoidosis patients.

Association of myelinated primary afferents impairment with mechanical allodynia in diabetic peripheral neuropathy: an experimental study in rats

To investigate the mechanisms underlying the efficacy of surgical treatment for painful diabetic peripheral neuropathy. Rats were initially divided into 3 groups (I, control rats, II, streptozotocin-induced diabetic rats, III, streptozotocin-induced diabetic rats with latex tube encircling the sciatic nerve without compression). When mechanical allodynia (MA) became stable in the third week, one third of group III rats were sacrificed and the remainder were further divided into subgroups depending on whether the latex tube was removed. Except for some rats in group III, all rats were sacrificed in the fifth week. Morphometric analysis of nerve fibers was performed. Expression level of GABA_B receptor protein in spinal dorsal horn was determined. Changes of GABA_B receptor within areas of primary afferents central terminal were identified. Chronic nerve compression caused by the interaction of diabetic nerves swelling and the encircling latex tube increased the incidence of MA in diabetic rats, and nerve decompression could ameliorate MA. In diabetic rats with MA, demyelination of myelinated fibers was noted and reduction of GABA_B receptor was mainly detected in the area of myelinated afferent central terminals. MA in DPN should be partially attributed to compression impairment of myelinated afferents, supporting the rationale for surgical decompression.

Role of peripheral and central TRPV1 receptors in facial heat hyperalgesia in streptozotocin-induced diabetic rats

There is increasing evidence that diabetes may be related to sensory changes in the trigeminal system. Long lasting facial heat hyperalgesia has been described in diabetic rats, but the mechanisms remain to be elucidated. Herein, the contribution of peripheral and central TRPV1 receptors to facial heat hyperalgesia in diabeticrats was investigated. Diabetes was induced in male Wistar rats by streptozotocin (60mg/kg, i.p) and facial heat hyperalgesia was assessed once a week up to four weeks. The role of TRPV1 receptors in the heat hyperalgesia in diabetic rats was evaluated through: 1) the ablation of TRPV1 receptors by resiniferatoxin (RTX) treatment and 2) injection of the TRPV1 antagonist, capsazepine, into the upper lip, trigeminal ganglion or medullary subarachnoid space, at doses that completed prevented the heat hyperalgesia induced by capsaicin in naïve rats. Western blot was used to estimate the changes in TRPV1 expression in diabetic rats. Diabetic rats exhibited facial heat hyperalgesia from the first up to the fourth week after streptozotocin injection, which was prevented by insulin treatment. Ablation of TRPV1-expressing fibers prevented facial hyperalgesia in diabetic rats. Capsazepine injection in all sites resulted in significant reduction of facial heat hyperalgesia in diabetic rats. Diabetic rats exhibited a significant decrease in TRPV1 expression in the trigeminal nerve, increased expression in the trigeminal ganglion and no changes in subnucleus caudalis when compared to normoglycemic ones. In conclusion, our results suggest that facial heat hyperalgesia in diabetic rats is maintained by peripheral and central TRPV1 receptors activation.

Psychometric properties of the painDETECT questionnaire in rheumatoid arthritis, psoriatic arthritis and spondyloarthritis: Rasch analysis and test-retest reliability

Background

Pain is inherent in rheumatoid arthritis (RA), psoriatic arthritis (PsA) and spondyloarthritis (SpA) and traditionally considered to be of nociceptive origin. Emerging data suggest a potential role of augmented central pain mechanisms in subsets of patients, thus, valid instruments that can identify underlying pain mechanisms are needed. The painDETECT questionnaire (PDQ) was originally designed to differentiate between pain phenotypes. The objectives were to evaluate the psychometric properties of the PDQ in patients with inflammatory arthritis by applying Rasch analysis and to explore the reliability of pain classification by test-retest.

Methods

For the Rasch analysis 900 questionnaires from patients with RA, PsA and SpA (300 per diagnosis) were extracted from ‘the DANBIO painDETECT study’. The analysis was directed at the seven items assessing somatosensory symptoms and included: 1) the performance of the six-category Likert scale; 2) whether a unidimensional construct was defined; 3) the reliability and precision of estimates. Another group of 30 patients diagnosed with RA, PsA or SpA participated in a test-retest study. Intraclass Correlation Coefficients (ICC) and classification consistency were calculated.

Results

The Rasch analysis revealed: (1) Acceptable psychometric rating scale properties; the frequency distribution peaked in category 0 except for item 5, threshold calibration >10 observations per category, no disorder in the category measures for all items, scale category outfit Mnsq <2.0, small distances (<1.4 logits) between thresholds for category 1, 2 and 3 for all items. (2) The principal component analysis supported unidimensionality; the standardized residuals showed that 53.7% of total variance was explained by the measure and the magnitude of first contrast had an eigenvalue of 1.5, no misfitting items, clinical insignificant different item hierarchies across diagnoses (DIF < 0.5 logits). (3) A targeted item-person map, person and item separation indices of 1.88(reliability = 0.78), and 13.04 (reliability = 0.99). The test-retest revealed: ICC: RA 0.86(0.56–0.96), PsA 0.96(0.74–0.99), SpA 0.93(0.76–98), overall 0.94(0.84–0.98). Classification consistency was: RA 70%, PsA 80%, SpA 90%, overall 80%.

Conclusion

The results support that the PDQ can be used as a classification instrument and assist identification of underlying pain-mechanisms in patients suffering from inflammatory arthritis.

Self-Reported Neuropathic Pain Characteristics of Women With Provoked Vulvar Pain: A Preliminary Investigation

BACKGROUND

Provoked vestibulodynia (PVD) is a common chronic genital pain condition affecting approximately 12% of premenopausal women. Although parallels have been drawn between PVD and neuropathic pain (NP), no studies have examined self-reported NP characteristics in PVD.

AIM

To explore pain symptoms that resemble NP reported by those with PVD and compare responses with those with an established NP condition.

METHODS

Women with provoked vulvar pain (PVP; n = 65) completed online questionnaires designed to assess characteristics of NP. Responses were compared with those of women with postherpetic neuralgia (PHN; n = 30).

OUTCOMES

In addition to a range of descriptive questions, participants completed the McGill Pain Questionnaire, the Self-Complete Leeds Assessment of Neuropathic Signs and Symptoms (S-LANSS), the Neuropathic Pain Symptom Inventory (NPSI), and the Pain Quality Assessment Scale (PQAS).

RESULTS

PVP exhibits some neuropathic characteristics, typically evoked pain (as opposed to the more constant pain of PHN) indicative of allodynia and hyperalgesia. Specifically, women with PVP scored, on average, higher than the NP cutoff on the S-LANSS, and there were no significant differences between women with PVP and those with PHN on some NPSI subscales. However, women with PHN reported more NP symptoms on the PQAS, S-LANSS, and other NPSI subscales.

CLINICAL IMPLICATIONS

Validated NP questionnaires could be of particular use for health care professionals who need a more efficient way to assess symptoms of patients with PVP and should be included in future studies investigating the mechanisms and treatment of this pain.

STRENGTHS AND LIMITATIONS

This study takes a unique approach to the examination of PVP by using multiple validated NP measures to compare pain characteristics with those of a group of participants with PHN, an established NP condition. However, it is limited by self-reported data not confirmed with clinical examination, small size of the PHN group, and the severity of the pain experienced in the PVP group.

CONCLUSION

Women with PVP report some symptoms suggestive of NP characteristics, and future research should use NP measures in addition to physical examinations to further investigate the mechanisms that maintain this pain condition. Dargie E, Gilron I, Pukall CF. Self-Reported Neuropathic Pain Characteristics of Women With Provoked Vulvar Pain: A Preliminary Investigation. J Sex Med 2017;14:577-591.

Symptom profiles in the painDETECT Questionnaire in patients with peripheral neuropathic pain stratified according to sensory loss in quantitative sensory testing

The painDETECT Questionnaire (PDQ) is commonly used as a screening tool to discriminate between neuropathic pain (NP) and nociceptive pain, based on the self-report of symptoms, including pain qualities, numbness, and pain to touch, cold, or heat. However, there are minimal data about whether the PDQ is differentially sensitive to different sensory phenotypes in NP. The aim of the study was to analyze whether the overall PDQ score or its items reflect phenotypes of sensory loss in NP as determined by quantitative sensory testing. An exploratory analysis in the Innovative Medicines Initiative Europain and Neuropain database was performed. Data records of 336 patients identified with NP were grouped into sensory profiles characterized by (1) no loss of sensation, (2) loss of thermal sensation, (3) loss of mechanical sensation, and (4) loss of thermal and mechanical sensation. painDETECT Questionnaire profiles were analyzed in a 2-factor analysis of variance. Patients with loss of thermal sensation (2 and 4) significantly more often reported pain evoked by light touch, and patients with loss of mechanical sensation (3 and 4) significantly more often reported numbness and significantly less often burning sensations and pain evoked by light touch. Although the PDQ was not designed to assess sensory loss, single items reflect thermal and/or mechanical sensory loss at group level, but because of substantial variability, the PDQ does not allow for individual allocation of patients into sensory profiles. It will be useful to develop screening tools according to the current definition of NP.

Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations

There is tremendous interpatient variability in the response to analgesic therapy (even for efficacious treatments), which can be the source of great frustration in clinical practice. This has led to calls for "precision medicine" or personalized pain therapeutics (ie, empirically based algorithms that determine the optimal treatments, or treatment combinations, for individual patients) that would presumably improve both the clinical care of patients with pain and the success rates for putative analgesic drugs in phase 2 and 3 clinical trials. However, before implementing this approach, the characteristics of individual patients or subgroups of patients that increase or decrease the response to a specific treatment need to be identified. The challenge is to identify the measurable phenotypic characteristics of patients that are most predictive of individual variation in analgesic treatment outcomes, and the measurement tools that are best suited to evaluate these characteristics. In this article, we present evidence on the most promising of these phenotypic characteristics for use in future research, including psychosocial factors, symptom characteristics, sleep patterns, responses to noxious stimulation, endogenous pain-modulatory processes, and response to pharmacologic challenge. We provide evidence-based recommendations for core phenotyping domains and recommend measures of each domain.

Patient-reported neuropathic pain in adolescent and young adult cancer patients

BACKGROUND

Neuropathic pain, a known complication of cancer and its treatments, negatively impacts quality of life. There are limited data using screening tools to aid in the diagnosis of neuropathic pain in cancer patients. Our primary objective was to determine the proportion of adolescent and young adult cancer patients reporting neuropathic pain on a patient-completed, neuropathic pain screening tool.

PROCEDURES

This prospective, cohort study enrolled patients 14-39 years of age who were receiving therapy for primary cancer diagnosis, cancer relapse, or had recently completed treatment. The painDETECT, a patient-completed, neuropathic pain screening tool used down to age 14, was administered a maximum of three times in on-therapy patients and once in off-therapy patients. Provider documentation of neuropathic pain at the corresponding visit was abstracted from the medical record.

RESULTS

Seventy-eight patients participated. Median (interquartile range) age at study enrollment was 18.1 (16-19.4) years and 47% were female. Cancer diagnoses included 41% leukemia, 26% solid tumor, 23% lymphoma, and 10% central nervous system tumor. The proportion of patients reporting neuropathic pain was 26% (95% confidence interval [CI] 16-40%) in on-therapy patients and 11% (95% CI 3-27%) in off-therapy patients. In patients reporting neuropathic pain, only 26% had a clinical diagnosis of neuropathic pain documented in the medical record at the corresponding visit.

CONCLUSIONS

Neuropathic pain occurs in one in four adolescents and young adults receiving cancer therapy. Use of screening tools may increase the detection of neuropathic pain in adolescents and young adults receiving cancer therapy and could ultimately improve pain treatment.

Regenerative peripheral neuropathic pain: novel pathological pain, new therapeutic dimension

After peripheral nerve damage, injured or stressed primary sensory neurons (PSNs) transmitting pathological pain (pathopain) sensitize central nervous system (CNS) neural circuits and determine behavioral phenotypes of peripheral neuropathic pain (PNP). Therefore, phenotypic profiling of pathopain-transmitting PSNs is vital for probing and discovering PNP conditions. Following peripheral nerve injuries (PNIs), PNP might be potentially transmitted by distinct classes of damaged or stressed PSNs, such as axotomized PSNs without regeneration (axotomy-non-regenerative neurons), axotomized PSNs with accurate regeneration (axotomy-regenerative neurons), and spared intact PSNs adjacent to axotomized neurons (axotomy-spared neurons). Both axotomy-non-regenerative neurons and axotomy-spared neurons have been definitely shown to participate in specific PNP transmission. However, whether axotomy-regenerative neurons could transmit PNP with unique features has remained unclear. Recent studies in rodent models of axonotmesis have clearly demonstrated that axotomy-regenerative neurons alone transmit persistent pathological pain with unique behavioral phenotypes. In this review, we exclusively review this novel category of PNP, reasonably term it ‘regenerative peripheral neuropathic pain’, and finally discuss its potential clinical significance as a new therapeutic dimension for PNIs beyond nerve regeneration.

European consensus-based (S2k) Guideline on the Management of Herpes Zoster - guided by the European Dermatology Forum (EDF) in cooperation with the European Academy of Dermatology and Venereology (EADV), Part 2: Treatment

Herpes zoster (HZ, shingles) is a frequent medical condition which may severely impact the quality of life of affected patients. Different therapeutic approaches to treat acute HZ are available. The aim of this European project was the elaboration of a consensus-based guideline on the management of patients who present with HZ, considering different patient populations and different localizations. This interdisciplinary guideline aims at an improvement of the outcomes of the acute HZ management concerning disease duration, acute pain and quality of life of the affected patients and at a reduction in the incidence of postherpetic neuralgia (PHN) and other complications. The guideline development followed a structured and pre-defined process, considering the quality criteria for guidelines development as suggested by the AGREE II instrument. The steering group was responsible for the planning and the organization of the guideline development process (Division of Evidence-Based Medicine, dEBM). The expert panel was nominated by virtue of clinical expertise and/or scientific experience and included experts from the fields of dermatology, virology/infectiology, ophthalmology, otolaryngology, neurology and anaesthesiology. Recommendations for clinical practice were formally consented during the consensus conference, explicitly considering different relevant aspects. The guideline was approved by the commissioning societies after an extensive internal and external review process. In this second part of the guideline, therapeutic interventions have been evaluated. The expert panel formally consented recommendations for the treatment of patients with HZ (antiviral medication, pain management, local therapy), considering various clinical situations. Users of the guideline must carefully check whether the recommendations are appropriate for the context of intended application. In the setting of an international guideline, it is generally important to consider different national approaches and legal circumstances with regard to the regulatory approval, availability and reimbursement of diagnostic and therapeutic interventions.

Assessment of Chronic Pain: Domains, Methods, and Mechanisms

Accurate classification of chronic pain conditions requires reliable and valid pain assessment. Moreover, pain assessment serves several additional functions, including documenting the severity of the pain condition, tracking the longitudinal course of pain, and providing mechanistic information. Thorough pain assessment must address multiple domains of pain, including the sensory and affective qualities of pain, temporal dimensions of pain, and the location and bodily distribution of pain. Where possible, pain assessment should also incorporate methods to identify pathophysiological mechanisms underlying the pain. This article discusses assessment of chronic pain, including approaches available for assessing multiple pain domains and for addressing pathophysiological mechanisms. We conclude with recommendations for optimal pain assessment.

PERSPECTIVE

Pain assessment is a critical prerequisite for accurate pain classification. This article describes important features of pain that should be assessed, and discusses methods that can be used to assess the features and identify pathophysiological mechanisms contributing to pain.

Symptom-Based Treatment of Neuropathic Pain in Spinal Cord-Injured Patients: A Randomized Crossover Clinical Trial

OBJECTIVE

The objective of this study was to identify the differences in medication effect according to pain characteristics in spinal cord-injured patients.

METHODS

This study is a prospective, randomized, crossover study. Fifty-five patients and 66 locations of neuropathic pain were included. Pain was classified into four spontaneous characteristics and three evoked pain characteristics. Oxcarbazepine (Na channel blocker) and pregabalin (calcium channel α2-δ ligand medication) were tried. Patients were divided into two groups: evoked pain present and evoked pain absent. Overall average visual analog scale was obtained.

RESULTS

Oxcarbazepine was significantly more effective for patients without evoked pain than in those with it for electrical, burning, and pricking pain. The effect of pregabalin was not different regarding the presence or absence of evoked pain for all pain categories, except burning pain. In patients with evoked pain, pregabalin was shown to be significantly more effective for electrical pain, allodynia, and heat hyperalgesia than oxcarbazepine. In the evoked pain absent group, oxcarbazepine showed greater improvement than pregabalin but was not significant.

CONCLUSIONS

In summary, the phenotype of neuropathic pain was associated with the efficacy of different pharmacologic treatments. Symptom-based treatment, therefore, can lead to more efficient analgesia.

Mapping painDETECT, a neuropathic pain screening tool, to the EuroQol (EQ-5D-3L)

PURPOSE

To map relationships between painDETECT, a neuropathic pain (NeP) screening tool, and EQ-5D-3L health status in a real-world setting.

METHODS

Patients with physician-confirmed NeP and painDETECT score classifications of nociceptive (n = 79), transitional (n = 141), and NeP (n = 386) completed the EuroQol (EQ-5D-3L), which evaluates Mobility, Self-Care, Usual Activities, Pain/Discomfort, and Anxiety/Depression with three ordinal response levels ("no problem," "some problems," or "extreme problems/unable to do"), and has a health status thermometer (0 = worst health, 100 = perfect health). Multiple linear and logistic regressions were performed (adjusted for age, gender, race, ethnicity, time since NeP diagnosis, number of comorbidities, NeP conditions).

RESULTS

Unadjusted mean (±SD) EQ-5D-3L thermometer scores showed poorer health status across painDETECT classifications from nociceptive (67.3 ± 22.1) to transitional (62.3 ± 20.9) to NeP (53.7 ± 21.8), as did utility scores, 0.695 ± 0.206, 0.615 ± 0.216, and 0.506 ± 0.216. In general, the highest odds of health problems were observed for NeP and the lowest for nociceptive, e.g., the NeP group was 6.2 (95 % confidence interval 3.4-11.4) times as likely to have a more severe problem of Usual Activities compared with the nociceptive group. Relative to nociceptive and transitional, NeP had lower adjusted mean thermometer scores, by 12.1 (P < 0.0001) and 7.8 (P = 0.0004) points, respectively, and lower mean utility scores by 0.157 (P < 0.0001) and 0.092 points (P < 0.0001).

CONCLUSIONS

This study, the first to map relationships between painDETECT and the EQ-5D-3L in a real-world setting, indicates that the patient burden with respect to pain classification can be characterized and quantified by decrements in health status overall and in specific domains. These data support the psychometric soundness of painDETECT, enhancing its use in pain management.

Painful neuropathy: Mechanisms

Painful neuropathy, like the other complications of diabetes, is a growing healthcare concern. Unfortunately, current treatments are of variable efficacy and do not target underlying pathogenic mechanisms, in part because these mechanisms are not well defined. Rat and mouse models of type 1 diabetes are frequently used to study diabetic neuropathy, with rats in particular being consistently reported to show allodynia and hyperalgesia. Models of type 2 diabetes are being used with increasing frequency, but the current literature on the progression of indices of neuropathic pain is variable and relatively few therapeutics have yet been developed in these models. While evidence for spontaneous pain in rodent models is sparse, measures of evoked mechanical, thermal and chemical pain can provide insight into the pathogenesis of the condition. The stocking and glove distribution of pain tantalizingly suggests that the generator site of neuropathic pain is found within the peripheral nervous system. However, emerging evidence demonstrates that amplification in the spinal cord, via spinal disinhibition and neuroinflammation, and also in the brain, via enhanced thalamic activity or decreased cortical inhibition, likely contribute to the pathogenesis of painful diabetic neuropathy. Several potential therapeutic strategies have emerged from preclinical studies, including prophylactic treatments that intervene against underlying mechanisms of disease, treatments that prevent gains of nociceptive function, treatments that suppress enhancements of nociceptive function, and treatments that impede normal nociceptive mechanisms. Ongoing challenges include unraveling the complexity of underlying pathogenic mechanisms, addressing the potential disconnect between the perceived location of pain and the actual pain generator and amplifier sites, and finding ways to identify which mechanisms operate in specific patients to allow rational and individualized choice of targeted therapies.

Characterizing individual painDETECT symptoms by average pain severity

Background

painDETECT is a screening measure for neuropathic pain. The nine-item version consists of seven sensory items (burning, tingling/prickling, light touching, sudden pain attacks/electric shock-type pain, cold/heat, numbness, and slight pressure), a pain course pattern item, and a pain radiation item. The seven-item version consists only of the sensory items. Total scores of both versions discriminate average pain-severity levels (mild, moderate, and severe), but their ability to discriminate individual item severity has not been evaluated.

Methods

Data were from a cross-sectional, observational study of six neuropathic pain conditions (N=624). Average pain severity was evaluated using the Brief Pain Inventory-Short Form, with severity levels defined using established cut points for distinguishing mild, moderate, and severe pain. The Wilcoxon rank sum test was followed by ridit analysis to represent the probability that a randomly selected subject from one average pain-severity level had a more favorable outcome on the specific painDETECT item relative to a randomly selected subject from a comparator severity level.

Results

A probability >50% for a better outcome (less severe pain) was significantly observed for each pain symptom item. The lowest probability was 56.3% (on numbness for mild vs moderate pain) and highest probability was 76.4% (on cold/heat for mild vs severe pain). The pain radiation item was significant (P<0.05) and consistent with pain symptoms, as well as with total scores for both painDETECT versions; only the pain course item did not differ.

Conclusion

painDETECT differentiates severity such that the ability to discriminate average pain also distinguishes individual pain item severity in an interpretable manner. Pain-severity levels can serve as proxies to determine treatment effects, thus indicating probabilities for more favorable outcomes on pain symptoms.