Changes in cutaneous innervation in patients with chronic pain after burns

Functional Brain Changes Following Burn Injury: A Narrative Review

BACKGROUND

Burn injuries cause significant motor and sensory dysfunctions that can negatively impact burn survivors' quality of life. The underlying mechanisms of these burn-induced dysfunctions have primarily been associated with damage to the peripheral neural architecture, however, evidence points to a systemic influence of burn injury. Central nervous system (CNS) reorganizations due to inflammation, afferent dysfunction, and pain could contribute to persistent motor and sensory dysfunction in burn survivors. Recent evidence shows that the capacity for neuroplasticity is associated with self-reported functional recovery in burn survivors.

OBJECTIVE

This review first outlines motor and sensory dysfunctions following burn injury and critically examines recent literature investigating the mechanisms mediating CNS reorganization following burn injury. The review then provides recommendations for future research and interventions targeting the CNS such as non-invasive brain stimulation to improve functional recovery.

CONCLUSIONS

Directing focus to the CNS following burn injury, alongside the development of non-invasive methods to induce functionally beneficial neuroplasticity in the CNS, could advance treatments and transform clinical practice to improve quality of life in burn survivors.

Scrambler Therapy for Chronic Pain after Burns and Its Effect on the Cerebral Pain Network: A Prospective, Double-Blinded, Randomized Controlled Trial

Chronic pain is common after burn injuries, and post-burn neuropathic pain is the most important complication that is difficult to treat. Scrambler therapy (ST) is a non-invasive modality that uses patient-specific electrocutaneous nerve stimulation and is an effective treatment for many chronic pain disorders. This study used magnetic resonance imaging (MRI) to evaluate the pain network-related mechanisms that underlie the clinical effect of ST in patients with chronic burn-related pain. This prospective, double-blinded, randomized controlled trial (ClinicalTrials.gov: NCT03865693) enrolled 43 patients who were experiencing chronic neuropathic pain after unilateral burn injuries. The patients had moderate or greater chronic pain (a visual analogue scale (VAS) score of ≥5), despite treatment using gabapentin and other physical modalities, and were randomized 1:1 to receive real or sham ST sessions. The ST was performed using the MC5-A Calmare device for ten 45 min sessions (Monday to Friday for 2 weeks). Baseline and post-treatment parameters were evaluated subjectively using the VAS score for pain and the Hamilton Depression Rating Scale; MRI was performed to identify objective central nervous system changes by measuring the cerebral blood volume (CBV). After 10 ST sessions (two weeks), the treatment group exhibited a significant reduction in pain relative to the sham group. Furthermore, relative to the pre-ST findings, the post-ST MRI evaluations revealed significantly decreased CBV in the orbito-frontal gyrus, middle frontal gyrus, superior frontal gyrus, and gyrus rectus. In addition, the CBV was increased in the precentral gyrus and postcentral gyrus of the hemisphere associated with the burned limb in the ST group, as compared with the CBV of the sham group. Thus, a clinical effect from ST on burn pain was observed after 2 weeks, and a potential mechanism for the treatment effect was identified. These findings suggest that ST may be an alternative strategy for managing chronic pain in burn patients.

Combination of Battlefield Acupuncture and Local Point Acupuncture for Post Laparotomy Scar Pain

Background: Scar pain is a residual symptom of a wound that can cause physiologic and psychologic disorders in patients. In addition to mechanical stimulation in nociceptive fibers, pain can be caused by a neuroma-an adhesion between the layers of skin and fascia that disrupts blood flow around the scar-as well as an increase in peptidergic nerve-fiber density due to dysregulation between synthesis and degradation of collagen tissue that cause abnormal scar formation. Research has shown that ear acupuncture is effective for management of acute pain, including scar pain. Acupuncture in the local area of the scar is also effective for reducing pain significantly. The combination of these 2 therapies is expected to be effective for management of scar pain in cases that have not improved for 4 years. Case: A 69-year-old woman, with a history of a laparotomy 4 years ago, came to the RSCM acupuncture outpatient unit with severe pain in her stomach. The pain was located in a 30-cm long laparotomy wound that ran between the xiphoideus process and the umbilicus, and felt like a rope binding and pressing upward in the area. Manual acupuncture was given at a Battlefield Acupuncture (BFA) point, combined with acupuncture to local point on the scar. Results: She had with a positive vascular autonomic sign response for 30 minutes at each session. At the end of her 12th therapy session, she reported that she was pain-free and did not experience any severe side-effects. Conclusion: A combination of BFA with local-point acupuncture was effective in reducing the severe pain of caused by a post-laparotomy scar.

Sensory processing and detection thresholds of burn-injured patients: A comparison to normative data

OBJECTIVE

Emerging evidence suggests that individual levels of sensory sensitivity may impact treatment outcomes for people recovering from burn injuries. For example, individuals with higher levels of sensory sensitivity were less adherent with compression garment wear, often used for scar management. The purpose of this study was to characterise sensory patterns for a sample of burn-injured patients as a cohort, using normative data as the reference. As different patterns of sensory processing can have implications clinically, understanding this at the cohort level may provide valuable insight for therapy.

METHOD

This was a secondary analysis of data collected during a cross-sectional study. Adults (N = 117) attending the Professor Stuart Pegg Adult Burns Unit outpatient clinic completed the Adolescent/Adult Sensory Profile and the following quantitative sensory tests: two-point discrimination; mechanical detection threshold; and pressure pain threshold.

RESULTS

Compared to matched normative data, burn-injured patients reported higher levels of sensory sensitive and avoiding patterns, and experienced lower detection thresholds for touch and pain.

CONCLUSIONS

Higher reports of sensory sensitivity and sensory avoiding, and lower thresholds for touch and pain, have been correlated with tactile defensiveness. Tactile defensiveness has been associated with social withdrawal and isolation, all of which could contribute to decreased engagement in therapy. The ways in which these sensory characteristics impact on burn-related treatments, such as compression garment adherence, warrant further investigation.

Analysis of the predictors of hypertrophic scarring pain and neuropathic pain after burn

INTRODUCTION

Burn hypertrophic scarring pain is a common and perennial complaint which not only affects patients' quality of life, but also their recovery and reintegration. Physical therapy and medicine regimens are all available for the treatment of hypertrophic scarring pain. Unfortunately, the efficacy of clinical practice is not very satisfactory and the management of hypertrophic scarring pain remains challenging. Therefore, it is of utmost importance to explore the risk factors for hypertrophic scarring pain and further identify whether it is neuropathic pain, aiming to guide the clinical therapy and help patients live a pain-free life.

METHODS

This retrospective study enrolled patients with postburn hypertrophic scarring pain between 2017 and 2020 in a burn center in Shanghai. Research objects were included strictly according to the inclusion criteria and every enrolled patient was included in the study only once. Demographic information, burn and scar characteristics, and pain scores were collected through the Changhai Hospital Medical Information System, patient questionnaire and physician assessment. Using SPSS 26.0 software, the data were first processed by descriptive statistics, and linear and logistic regression analyses were further employed to explore the significant factors.

RESULTS

The sample involving 123 patients was consisted of 56.9% males, 79.7% caused by fire with a median age 40.5 years, total body surface burn-area (TBSA) 44.4%, wound healing time of target scar 57.9 days, hyperplasia time 9.3 months and the scar location mainly in the limbs (55.3%). Of all the included objects, the modified Vancouver Scar Scale (mVSS) total, visual analogue scale (VAS) score, brief pain inventory (BPI) total and the percentage of neuropathic pain were 9.6, 3.3, 36.0 and 74.8%, respectively. Integrating covariates with a P value of <0.10 through preliminary univariate analysis, multivariable linear regression showed sex (P = 0.049), age (P = 0.020), target scar location (P = 0.017, P = 0.254), and pliability (P = 0.016) were linked with severe VAS score; and burn depth of target scar (P = 0.023), hyperplasia time (P = 0.027, P = 0.001), vascularity (P = 0.028), and pliability (P = 0.001) were associated with higher BPI score. Adjusting for potential confounders, hyperplasia time (P = 0.005, P = 0.039) was found to be the only independent risk factor for hypertrophic scarring neuropathic pain in the multivariate logistic regression analysis, with mVSS total of P = 0.062.

CONCLUSIONS

The model in our study has clarified that sex, age, target scar location, burn depth of target scar, hyperplasia time, and vascularity, especially pliability, may provide excellent prediction of hypertrophic scarring pain outcome; for neuropathic pain, only hyperplasia time has further prospects, with mVSS total as a potential forecast. In an era increasingly aware of life quality, this work may contribute to the elaboration of strategies to hypertrophic scarring pain management, provide an individualized therapy, and help patients live a pain-free life.

Nerve Pain after Burn Injury: A Proposed Etiology-Based Classification

BACKGROUND

Understanding the mechanism of nerve injury may facilitate managing burn-related nerve pain. This proposed classification, based on cause of nerve injury, was developed to enhance the understanding and management of burn-related nerve pain.

METHODS

This retrospective investigation included patients aged 15 years or older admitted to the burn center from 2014 to 2019. Burn-related nerve pain was patient-reported and clinically assessed as pain 6 months or more after burn injury, unrelated to preexisting illnesses/medications. The pain classification consisted of direct nerve injury, nerve compression, electrical injury, and nerve dysfunction secondary to systemic injury. The four categories were statistically analyzed between groups, using 52 variables.

RESULTS

Of the 1880 consecutive burn patients, 113 developed burn-related nerve pain and were eligible for validation of the classification: direct nerve injury, n = 47; nerve compression, n = 12; electrical injury, n = 7; and nerve dysfunction secondary to systemic injury, n = 47. Factors, significantly increased, that distinguished one category from another were as follows: for direct nerve injury, continuous symptoms (p < 0.001), refractory nerve release response (p < 0.001), nerve repair (p < 0.001), and pruritus (p < 0.001); for nerve compression, Tinel signs (p < 0.001), shooting pain (p < 0.001), numbness (p = 0.003), intermittent symptoms (p < 0.001), increased percentage total body surface area burned (p = 0.019), surgical procedures (p < 0.001), and nerve release (p < 0.001); and for electrical injury, Tinel sign (p < 0.001), intermittent symptoms (p = 0.002), amputations (p = 0.002), fasciotomies (p < 0.001), and nerve release (p < 0.001). Nerve dysfunction secondary to systemic injury was distinguished by significantly less Tinel signs (p < 0.001), shooting pain (p < 0.001), numbness and tingling (p < 0.001), pruritus (p < 0.001), fascial excision (p = 0.004), skin grafts (p < 0.001), amputation (p = 0.004), nerve releases (p < 0.001), and third-degree burns (p = 0.002).

CONCLUSION

A classification consisting of direct nerve injury, nerve compression, electrical injury, and nerve dysfunction secondary to systemic injury is presented that may guide patient management and research methods, with the goal of improving pain outcomes in burn-related nerve pain.

Plastic Changes in Pain and Motor Network Induced by Chronic Burn Pain

Musculoskeletal diseases with chronic pain are difficult to control because of their association with both central as well as the peripheral nervous system. In burn patients, chronic pain is one of the major complications that cause persistent discomfort. The peripheral mechanisms of chronic pain by burn have been greatly revealed through studies, but the central mechanisms have not been identified. Our study aimed to characterize the cerebral plastic changes secondary to electrical burn (EB) and non-electrical burn (NEB) by measuring cerebral blood volume (CBV). Sixty patients, twenty with electrical burn (EB) and forty with non-electrical burn (NEB), having chronic pain after burn, along with twenty healthy controls, participated in the study. Voxel-wise comparisons of relative CBV maps were made among EB, NEB, and control groups over the entire brain volume. The CBV was measured as an increase and decrease in the pain and motor network including postcentral gyrus, frontal lobe, temporal lobe, and insula in the hemisphere associated with burned limbs in the whole burn group. In the EB group, CBV was decreased in the frontal and temporal lobes in the hemisphere associated with the burned side. In the NEB group, the CBV was measured as an increase or decrease in the pain and motor network in the postcentral gyrus, precentral gyrus, and frontal lobe of the hemisphere associated with the burn-affected side. Among EB and NEB groups, the CBV changes were not different. Our findings provide evidence of plastic changes in pain and motor network in patients with chronic pain by burn.

Chronic Neuropathic Pain Following Hand Burns: Etiology, Treatment, and Long-Term Outcomes

PURPOSE

Chronic neuropathic pain (CNP) after burn injury to the hand/upper extremity is relatively common, but not well described in the literature. This study characterizes patients with CNP after hand/upper extremity burns to help guide risk stratification and treatment strategies. We hypothesize that multiple risk factors contribute to the development of CNP and refractory responses to treatment.

METHODS

Patients older than 15 years admitted to the burn center after hand/upper extremity burns, from January 1, 2014, through January 1, 2019, were included. Chronic neuropathic pain was defined as self-described pain for longer than 6 months after burn injury, not including pain due to preexisting illness/medications. Two analyses were undertaken: (1) determining risk factors for developing CNP among patients with hand/upper extremity burns, and (2) determining risk factors for developing refractory pain (ie, nonresponsive to treatment) among hand/upper extremity burn patients with CNP.

RESULTS

Of the 914 patients who met the inclusion criteria, 55 (6%) developed CNP after hand/upper extremity burns. Twenty-nine of these patients (53%) had refractory CNP. Significant risk factors for developing CNP after hand/upper extremity burns included history of substance abuse and tobacco use. Among CNP patients, significant risk factors for developing refractory pain included symptoms of burning sensations. In all CNP patients, gabapentin and ascorbic acid were associated with significant decreases in pain scores on follow-up.

CONCLUSIONS

Substance abuse and tobacco use may contribute to the development of CNP after hand/upper extremity burns. Those who developed refractory CNP were more likely to use the pain descriptor, burning sensations. Pharmacological pain management with gabapentin or pregabalin and ascorbic acid may provide the most relief of CNP symptoms.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Autologous fat grafting for nerve regeneration and neuropathic pain: current state from bench-to-bedside

Despite recent advances in microsurgical techniques, functional recovery following peripheral nerve injury remains slow and inadequate. Poor peripheral nerve regeneration not only leaves patients with significant impairments, but also commonly leads to the development of debilitating neuropathic pain. Recent research has demonstrated the potential therapeutic benefits of adipose-derived stem cells, to enhance nerve regeneration. However, clinical translation remains limited due to the current regulatory burdens of the US FDA. A reliable and immediately translatable alternative is autologous fat grafting, where native adipose-derived stem cells present in the transferred tissue can potentially act upon regenerating axons. This review presents the scope of adipose tissue-based therapies to enhance outcomes following peripheral nerve injury, specifically focusing on their role in regeneration and ameliorating neuropathic pain.

Prevalence and associated predictors for patients developing chronic neuropathic pain following burns

BACKGROUND

Chronic pain, unrelated to the burn itself, can manifest as a long-term complication in patients sustaining burn injuries. The purpose of this study was to determine the prevalence of chronic neuropathic pain (CNP) and compare burn characteristics between patients who developed CNP and patients without CNP who were treated at a burn center.

METHODS

A single-center, retrospective analysis of 1880 patients admitted to the adult burn center was performed from 1 January 2014 to 1 January 2019. Patients included were over the age of 15 years, sustained a burn injury and were admitted to the burn center. CNP was diagnosed clinically following burn injury. Patients were excluded from the definition of CNP if their pain was due to an underlying illness or medication. Comparisons between patients admitted to the burn center with no pain and patients admitted to the burn center who developed CNP were performed.

RESULTS

One hundred and thirteen of the 1880 burn patients developed CNP as a direct result of burn injury over 5 years with a prevalence of 6.01%. Patients who developed CNP were a significantly older median age (54 years vs. 46 years, p = 0.002), abused alcohol (29% vs. 8%, p < 0.001),abused substances (31% vs. 9%, p < 0.001), were current daily smokers (73% vs. 33%, p < 0.001), suffered more full-thickness burns (58% vs. 43%, p < 0.001), greater median percent of total body surface area (%TBSA) burns (6 vs. 3.5, p < 0.001), were more often intubated on mechanical ventilation (33% vs. 14%, p < 0.001), greater median number of surgeries (2 vs. 0, p < 0.001) and longer median hospital length of stay (LOS) (10 days vs. 3 days, p < 0.001), compared to those who did not develop CNP, respectively. Median patient follow-up was 27 months.

CONCLUSIONS

The prevalence of CNP over 5 years was 6.01% in the burn center. Older ages, alcohol abuse, substance abuse, current daily smoking, greater percent of total body surface area (%TBSA) burns, third degree burns, being intubated on mechanical ventilation, having more surgeries and longer hospital LOS were associated with developing CNP following burn injury, compared to patients who did not develop CNP following burn injury.

Identification of Merkel cells associated with neurons in engineered skin substitutes after grafting to full thickness wounds

Engineered skin substitutes (ESS), prepared using primary human fibroblasts and keratinocytes with a biopolymer scaffold, were shown to provide stable closure of excised burns, but relatively little is known about innervation of ESS after grafting. This study investigated innervation of ESS and, specifically, whether Merkel cells are present in healed grafts. Merkel cells are specialized neuroendocrine cells required for fine touch sensation in skin. We discovered cells positive for keratin 20 (KRT20), a general marker for Merkel cells, in the basal epidermis of ESS after transplantation to mice, suggesting the presence of Merkel cells. Cells expressing KRT20 were not observed in ESS in vitro. However, widely separated KRT20-positive cells were observed in basal epidermis of ESS by 2 weeks after grafting. By 4 weeks, these cells increased in number and expressed keratins 18 and 19, additional Merkel cells markers. Putative Merkel cell numbers increased further between weeks 6 and 14; their densities varied widely and no specific pattern of organization was observed, similar to Merkel cell localization in human skin. KRT20-positive cells co-expressed epidermal markers E-cadherin and keratin 15, suggesting derivation from the epidermal lineage, and neuroendocrine markers synaptophysin and chromogranin A, consistent with their identification as Merkel cells. By 4 weeks after grafting, some Merkel cells in engineered skin were associated with immature afferents expressing neurofilament-medium. By 8 weeks, Merkel cells were complexed with more mature neurons expressing neurofilament-heavy. Positive staining for human leukocyte antigen demonstrated that the Merkel cells in ESS were derived from grafted human cells. The results identify, for the first time, Merkel cell-neurite complexes in engineered skin in vivo. This suggests that fine touch sensation may be restored in ESS after grafting, although this must be confirmed with future functional studies.

Efficacy of acupuncture in treating scars following tissue trauma

INTRODUCTION

Anecdotally, acupuncture is used in the treatment of scar tissue in order to improve scar quality and reduce symptoms of pain and pruritus. Unlike conditions such as lower back pain, knee osteoarthritis and migraines, there are no systematic reviews to confirm treatment efficacy. This systematic literature review aims to assess the current level of evidence for the use of acupuncture for treating abnormal scars such as hypertrophic or other symptomatic scars.

METHODS

A comprehensive database search was performed followed by reviewing reference lists, grey literature databases and Google Scholar. Study quality was assessed using the Oregon CONSORT STRICTA instrument (OCSI) for clinical trials and the Joanna Briggs Institute (JBI) checklist for case reports.

RESULTS

The search strategy discovered five case studies, one retrospective cohort study, one cohort study and three clinical trials that investigated the use of acupuncture for scars. Studies rated as low to moderate quality (26-50%) on the OCSI checklist due to lack of detailed reporting, use of non-validated outcome measures and heterogeneity of participant cohorts. Three case studies rated as moderate quality (5-6/8) and two as low quality (<2/8) on the JBI checklist.

DISCUSSION

All studies reported positive outcomes for the use of acupuncture for scar symptoms; however, treatment frequency, duration, number of treatments and points used varied between studies.

CONCLUSION

Acupuncture for the treatment of abnormal scars has a low level of evidence thus requiring further well-designed, controlled trials to be performed. Recommended treatment protocols for future studies have been provided.

Inflammatory Renin-Angiotensin System Disruption Attenuates Sensory Hyperinnervation and Mechanical Hypersensitivity in a Rat Model of Provoked Vestibulodynia

Vestibulodynia is characterized by perivaginal mechanical hypersensitivity, hyperinnervation, and abundant inflammatory cells expressing renin-angiotensin system proteins. We developed a tractable rat model of vestibulodynia to further assess the contributions of the renin-angiotensin system. Complete Freund's adjuvant injected into the posterior vestibule induced marked vestibular hypersensitivity throughout a 7-day test period. Numbers of axons immunoreactive for PGP9.5, calcitonin gene-related peptide, and GFRα2 were increased. Numbers of macrophages and T cells were also increased whereas B cells were not. Renin-angiotensin-associated proteins were abundant, with T cells as well as macrophages contributing to increased renin and angiotensinogen. Media conditioned with inflamed vestibular tissue promoted neurite sprouting by rat dorsal root ganglion neurons in vitro, and this was blocked by the angiotensin II receptor type 2 receptor antagonist PD123319 or by an angiotensin II function blocking antibody. Sensory axon sprouting induced by inflamed tissue was dependent on activity of angiotensin-converting enzyme or chymase, but not cathepsin G. Thus, vestibular Complete Freund's adjuvant injection substantially recapitulates changes seen in patients with provoked vestibulodynia, and shows that manipulation of the local inflammatory renin-angiotensin system may be a useful therapeutic strategy.

PERSPECTIVE

This study provides evidence that inflammation of the rat vestibule induces a phenotype recapitulating behavioral and cytological features of human vestibulodynia. The model confirms a crucial role of the local inflammatory renin-angiotensin system in hypersensitivity and hyperinnervation. Targeting this system holds promise for developing new nonopioid analgesic treatment strategies.

Calcitonin gene-related peptide and pain: a systematic review

BACKGROUND

Calcitonin gene-related peptide (CGRP) is widely distributed in nociceptive pathways in human peripheral and central nervous system and its receptors are also expressed in pain pathways. CGRP is involved in migraine pathophysiology but its role in non-headache pain has not been clarified.

METHODS

We performed a systematic literature search on PubMed, Embase and ClinicalTrials.gov for articles on CGRP and non-headache pain covering human studies including experimental studies and randomized clinical trials.

RESULTS

The literature search identified 375 citations of which 50 contained relevant original data. An association between measured CGRP levels and somatic, visceral, neuropathic and inflammatory pain was found. In 13 out of 20 studies in somatic pain conditions, CGRP levels had a positive correlation with pain. Increased CGRP levels were reported in plasma, synovial and cerebrospinal fluid in subjects with musculoskeletal pain. A randomized clinical trial on monoclonal antibody, which selectively binds to and inhibits the activity of CGRP (galcanezumab) in patients with osteoarthritis knee pain, failed to demonstrate improvement of pain compared with placebo. No studies to date have investigated the efficacy of monoclonal antibodies against CGRP receptor in non-headache pain conditions.

CONCLUSION

The present review revealed the association between measured CGRP levels and somatic, visceral, neuropathic and inflammatory pain. These data suggest that CGRP may act as a neuromodulator in non-headache pain conditions. However, more studies are needed to fully understand the role of CGRP in nociceptive processing and therapy of chronic pain.

Neuronal cytoskeletal gene dysregulation and mechanical hypersensitivity in a rat model of Rett syndrome

Children with Rett syndrome show abnormal cutaneous sensitivity. The precise nature of sensory abnormalities and underlying molecular mechanisms remain largely unknown. Rats with methyl-CpG binding protein 2 (MeCP2) mutation, characteristic of Rett syndrome, show hypersensitivity to pressure and cold, but hyposensitivity to heat. They also show cutaneous hyperinnervation by nonpeptidergic sensory axons, which include subpopulations encoding noxious mechanical and cold stimuli, whereas peptidergic thermosensory innervation is reduced. MeCP2 knockdown confined to dorsal root ganglion sensory neurons replicated this phenotype in vivo, and cultured MeCP2-deficient ganglion neurons showed augmented axonogenesis. Transcriptome analysis revealed dysregulation of genes associated with cytoskeletal dynamics, particularly those controlling actin polymerization and focal-adhesion formation necessary for axon growth and mechanosensory transduction. Down-regulation of these genes by topoisomerase inhibition prevented abnormal axon sprouting. We identified eight key affected genes controlling actin signaling and adhesion formation, including members of the Arhgap, Tiam, and cadherin families. Simultaneous virally mediated knockdown of these genes in Rett rats prevented sensory hyperinnervation and reversed mechanical hypersensitivity, indicating a causal role in abnormal outgrowth and sensitivity. Thus, MeCP2 regulates ganglion neuronal genes controlling cytoskeletal dynamics, which in turn determines axon outgrowth and mechanosensory function and may contribute to altered pain sensitivity in Rett syndrome.

Spinal Cord Stimulation Treatment for Persistent Pain After a Burn Injury: A Case Report

Spinal cord stimulation (SCS) is used to treat neuropathic pain, but there are no published studies on its use to treat burn pain. We used SCS to treat a 67-year-old man suffering from burn pain that could not be managed with high-dose opioids or adjuvant neuropathic analgesics. A trial of SCS markedly reduced the visual analog scale score for pain in the left lateral abdominal and gluteal regions. He underwent permanent implantation of a SCS and achieved an opioid-free state. This case suggests that SCS treatment is a therapeutic option for burn pain refractory to conventional therapy.

Myelinated and unmyelinated nerve fibers reinnervate tissue-engineered dermo-epidermal human skin analogs in an in vivo model

PURPOSE

The clinical application of autologous tissue-engineered skin analogs is an important strategy to cover large skin defects. Investigating biological dynamics, such as reinnervation after transplantation, is essential to improve the quality of such skin analogs. Previously, we have examined that our skin substitutes are reinnervated by host peripheral nerve fibers as early as 8 weeks after transplantation. Here, we wanted to investigate the presence and possible differences regarding myelinated and unmyelinated host nerve fibers 15 weeks after the transplantation of light and dark human tissue-engineered skin analogs.

METHODS

Human epidermal keratinocytes, melanocytes, and dermal fibroblasts were isolated from human light and dark skin biopsies. Keratinocytes and melanocytes were seeded on fibroblast-containing collagen type I hydrogels after expansion in culture. After additional culturing, the tissue-engineered dermo-epidermal skin analogs were transplanted onto full-thickness skin wounds created on the back of immuno-incompetent rats. Skin substitutes were excised and analyzed 15 weeks after transplantation. Histological sections were examined with regard to the ingrowth pattern of myelinated and unmyelinated nerve fibers into the skin analogs using markers, such as Substance P, NF200, and S100-Beta.

RESULTS

We found myelinated and unmyelinated peripheral host nerve fibers 15 weeks after transplantation in the dermal part of our human skin substitutes. In particular, we identified large-diameter-myelinated Aβ- and Aδ-fibers, and small-diameter C-fibers. Furthermore, we observed myelinated nerves in close proximity to CD31-positive blood capillaries. In the long run, both types of ingrown host fibers showed an identical pattern in both light and dark skin analogs.

CONCLUSION

Our data suggest that myelinated and unmyelinated peripheral nerves reinnervate human skin substitutes in a long-term in vivo transplantation assay. Our tissue-engineered skin analogs attract A- and C-fibers to supply both light and dark skin analogs. Potentially, this process restores skin sensitivity and has, therefore, a significant relevance with regard to future application of autologous pigmented dermo-epidermal skin substitutes onto patients.

The myofibroblast, a key cell in normal and pathological tissue repair

Myofibroblasts are characterized by their expression of α-smooth muscle actin, their enhanced contractility when compared to normal fibroblasts and their increased synthetic activity of extracellular matrix proteins. Myofibroblasts play an important role in normal tissue repair processes, particularly in the skin where they were first described. During normal tissue repair, they appear transiently and are then lost via apoptosis. However, the chronic presence and continued activity of myofibroblasts characterize many fibrotic pathologies, in the skin and internal organs including the liver, kidney and lung. More recently, it has become clear that myofibroblasts also play a role in many types of cancer as stromal or cancer-associated myofibroblast. The fact that myofibroblasts are now known to be key players in many pathologies makes understanding their functions, origin and the regulation of their differentiation important to enable them to be regulated in normal physiology and targeted in fibrosis, scarring and cancer.

Inflammation and cutaneous nervous system involvement in hypertrophic scarring

This study aimed to use a mouse model of hypertrophic scarring by mechanical loading on the dorsum of mice to determine whether the nervous system of the skin and inflammation participates in hypertrophic scarring. Results of hematoxylin-eosin and immunohistochemical staining demonstrated that inflammation contributed to the formation of a hypertrophic scar and increased the nerve density in scar tissue.Western blot assay verified that interleukin-13 expression was increased in scar tissue. These findings suggest that inflammation and the cutaneous nervous system play a role in hypertrophic scar formation.

Peripheral Innervation in Children With Global Developmental Delay: Biomarker for Risk for Self-Injurious Behavior?

The relation between somatosensory mechanisms and self-injury among children with neurologic impairments associated with developmental delay is not well understood. We evaluated the feasibility of procuring skin biopsies to examine epidermal nerve fiber density and reported self-injury. Following informed parental consent, epidermal skin biopsies were obtained from a distal leg site with no pre-existing skin damage from 11 children with global developmental delay (55% male; mean age = 36.8 months, 17-63 months). Visual microscopic examination and quantitative analyses showed extremely high epidermal nerve fiber density values for some children. Children with reported self-injury (5/11) had significantly (P < .02) greater density values (138.8, standard deviation = 45.5) than children without self-injury (80.5, standard deviation = 17.5). Results from this novel immunohistologic analysis of skin in very young children with neurodevelopmental delays suggest it may be a useful tool to study peripheral innervation as a possible sensory risk factor for self-injury.

The role of Eph receptors and Ephrins in the skin

Eph receptors and Ephrin ligands are widely expressed in the skin. Various studies have been carried out to identify the effects of these molecules on many aspects of skin development. Here we summarize the literature that has identified roles for Eph receptors and Ephrins in the skin, focusing mainly on the epidermis, hair follicles, and cutaneous innervation. This review may help direct and focus further investigations into the role of Eph receptors and Ephrins in the development, maintenance, and repair processes in cutaneous biology.

Autologous fat grafting alleviates burn-induced neuropathic pain in rats

BACKGROUND

The management of neuropathic pain after burn injury is a critical clinical issue. Autologous fat grafting has been shown to alleviate neuropathic pain in certain cases, but has not been shown to alleviate the pain associated with burn-induced scars. The authors assessed the effectiveness of autologous fat grafting for the management of pain in burn-induced scars.

METHODS

One paw of the experimental rats received a third-degree burn using a heated metal block. Neuropathic pain in the affected paw was assessed based on behavioral responses to thermal and mechanical stimuli. A graft (0.4 ml of autologous fat or a sham graft) was administered by injection to the burn scar and sham-burned paw. The animals were killed 4 weeks after the fat graft treatments; Masson trichrome stain of hind-paw skin and expression of phosphorylated p38 and OX42 in the dorsal horns of the spinal cords were examined.

RESULT

The third-degree burns were completely healed at 4 weeks. Burn-induced scarring caused mechanical allodynia and increased the expression of phosphorylated p38 and OX42 in spinal cord dorsal horn microglial cells. Autologous fat grafting significantly alleviated mechanical allodynia (p < 0.05), and immunohistochemistry showed that the expression of phosphorylated p38 and OX42 was significantly lower in spinal cord dorsal horn microglial cells 4 weeks after fat grafting (p < 0.05).

CONCLUSIONS

Autologous fat grafting is used daily in clinical practice. It is an effective treatment for the relief of burn-induced mechanical allodynia in rats. Further investigation of the clinical use of autologous fat grafting in burn patients is warranted.

Unilateral peripheral neuropathic pain: The role of neurodiagnostic skin biopsy

According to the current definition of neuropathic pain (“pain arising as a direct consequence of a lesion or disease affecting the somatosensory system”), the demonstration of a lesion or disease involving the somatosensory system is mandatory for the diagnosis of definite neuropathic pain. Although several methods are currently available for this aim, none is suitable for every type of disease (or lesion). Neurodiagnostic skin biopsy (NSB) is a relatively new technique for the diagnosis of peripheral nerve lesions. It is an objective method, completely independent from the patient’s complaining, based on immunohistochemical staining techniques that allow measurement of the density of the epidermal nerve fibers, currently considered the free nerve endings of small diameter (A-delta and C) afferent fibers. NSB has the important property of being used to investigate the skin, allowing obtaining a diagnosis of small fiber axonal neuropathy of peripheral nerves supplying every body part covered by skin. This feature appears to be very important, particularly in cases of unilateral nerve lesions, because it allows going beyond the possibilities of neurophysiological tests which are available only for a limited number of peripheral nerves. All these characteristics make NSB a precious instrument for the diagnosis of peripheral unilateral neuropathic pain.

Review of burn research for the year 2011

The year 2011 was another robust year for burn research. Over 1100 articles were published on a wide range of burn injury and treatment topics. In this review, we highlight some of the interesting and potentially influential research in the following areas: critical care, infection, inhalation injury, epidemiology, wound characterization and treatment, nutrition and metabolism, pain management, burn reconstruction, psychology, and rehabilitation. As in years past, burn injury research reflects the multidisciplinary and holistic care that is needed to treat this challenging injury condition.

Potential mechanisms for hypoalgesia induced by anti-nerve growth factor immunoglobulin are identified using autoimmune nerve growth factor deprivation

Nerve growth factor (NGF) antagonism has long been proposed as a chronic pain treatment. In 2010, the FDA suspended clinical trials using tanezumab, a humanized monoclonal anti-NGF antibody, to treat osteoarthritis due to worsening joint damage in 16 patients. Increased physical activity in the absence of acute pain which normally prevents self-harm was purported as a potential cause. Such an adverse effect is consistent with an extension of tanezumab's primary mechanism of action by decreasing pain sensitivity below baseline levels. In animal inflammatory pain models, NGF antagonism decreases intraepidermal nerve fiber (IENF) density and attenuates increases in expression of nociception-related proteins, such as calcitonin gene-related peptide (CGRP) and substance P (SP). Little is known of the effects of NGF antagonism in noninflamed animals and the hypoalgesia that ensues. In the current study, we immunized rats with NGF or cytochrome C (cytC) and examined (1) nocifensive behaviors with thermal latencies, mechanical thresholds, the hot plate test, and the tail flick test, (2) IENF density, and (3) expression of CGRP, SP, voltage-gated sodium channel 1.8 (Nav1.8), and glutaminase in subpopulations of dorsal root ganglion (DRG) neurons separated by size and isolectin B4 (IB4) labeling. Rats with high anti-NGF titers had delayed responses on the hot plate test but no other behavioral abnormalities. Delayed hot plate responses correlated with lower IENF density. CGRP and SP expression was decreased principally in medium (400-800 μm(2)) and small neurons (<400 μm(2)), respectively, regardless of IB4 labeling. Expression of Nav1.8 was only decreased in small and medium IB4 negative neurons. NGF immunization appears to result in a more profound antagonism of NGF than tanezumab therapy, but we hypothesize that decreases in IENF density and nociception-related protein expression are potential mechanisms for tanezumab-induced hypoalgesia.