A Descriptive Review of Neuropathic-Like Pain After Burn Injury

Physical and psychiatric recovery from burns

Burn injuries pose complex biopsychosocial challenges to recovery and improved comprehensive care. The physical and emotional sequelae of burns differ, depending on burn severity, individual resilience, and stage of development when they occur. Most burn survivors are resilient and recover, whereas some are more vulnerable and have complicated outcomes. Physical rehabilitation is affected by orthopedic, neurologic, and metabolic complications and disabilities. Psychiatric recovery is affected by pain, mental disorders, substance abuse, and burn stigmatization. Individual resilience, social supports, and educational or occupational achievements affect outcomes.

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.

On the horizon: research priorities in burns for the next decade

This review demonstrates that many advances have been made in burn care that have made dramatic differences in mortality, clinical outcomes, and quality of life in burn survivors; however, much work remains. In reality, the current standard of care is insufficient and we cannot be satisfied with the status quo. We must strive for the following goals: no deaths due to burn, no scarring, and no pain. These particular goals have only begun to be confronted.

Chronic pain following physical and emotional trauma: the station nightclub fire

OBJECTIVE

The purpose of this study was to evaluate factors associated with chronic pain in survivors of a large fire, including those with and without burn injury.

METHODS

This study employed a survey-based cross-sectional design to evaluate data from survivors of The Station nightclub fire. The primary outcome measure was the presence and severity of pain. Multiple linear regressions with a stepwise approach were used to examine relationships among variables. Variables considered included age, gender, marital status, burn injury, total body surface area, skin graft, pre-morbid employment, time off work, return to same employment, depression (Beck depression inventory, BDI), and post-traumatic stress (impact of event scale - revised).

RESULTS

Of 104 fire survivors, 27% reported pain at least 28 months after the event. Multiple factors associated with pain were assessed in the univariate analysis but only age (p = 0.012), graft (p = 0.009), and BDI score (p < 0.001) were significantly associated with pain in the multiple regression model.

DISCUSSION

A significant number of fire survivors with and without burn injuries experienced chronic pain. Depth of burn and depression were significantly associated with pain outcome. Pain management should address both physical and emotional risk factors in this population.

Extreme thermal noxious stimuli induce pain responses in zebrafish larvae

Exposing tissues to extreme high or low temperature leads to burns. Burned animals sustain several types of damage, from the disruption of the tissue to degeneration of axons projecting through muscle and skin. Such damage causes pain due to both inflammation and axonal degeneration (neuropathic-like pain). Thus, the approach to cure and alleviate the symptoms of burns must be twofold: rebuilding the tissue that has been destroyed and alleviating the pain derived from the burns. While tissue regeneration techniques have been developed, less is known on the treatment of the induced pain. Thus, appropriate animal models are necessary for the development of the best treatment for pain induced in burned tissues. We have developed a methodology in the zebrafish aimed to produce a new animal model for the study of pain induced by burns. Here, we show that two events linked to the onset of burn-induced inflammation and neuropathic-like pain in mammals, degeneration of axons innervating the affected tissues and over-expression of specific genes in sensory tissues, are conserved from zebrafish to mammals.

Outcome after burns: an observational study on burn scar maturation and predictors for severe scarring

Long-term outcome of burn scars as well as the relation with clinically relevant parameters has not been studied quantitatively. Therefore, we conducted a detailed analysis on the clinical changes of burn scars in a longitudinal setup. In addition, we focused on the differences in scar quality in relation to the depth, etiology of the burn wound and age of the patient. Burn scars of 474 patients were subjected to a scar assessment protocol 3, 6, and 12 months postburn. Three different age groups were defined (≤5, 5-18, and ≥18 years). The observer part of the patient and observer scar assessment scale revealed a significant (p < 0.001) improvement in scar quality at 12 months compared with the 3- and 6-month data. Predictors for severe scarring are depth of the wound (p < 0.001) and total body surface area burned (p < 0.001). Etiology (p = 0.753) and age (p > 0.230) have no significant influence on scar quality when corrected for sex, total body surface area burned, time, and age or etiology, respectively.

5% lidocaine medicated plaster use in children with neuropathic pain from burn sequelae

OBJECTIVE

Neuropathic pain is a challenge in children with burn sequelae. Although relatively infrequent, the intensity and chronicity of neuropathic pain negatively impact functionality and quality of life. The use of 5% lidocaine medicated plaster has not previously been reported in children. We explored the effectiveness and safety of 5% lidocaine medicated plaster to treat neuropathic pain in children with burn sequelae.

DESIGN

Three-month prospective, uncontrolled study.

SETTING

Corporation of Aid to Burned Children (COANIQUEM), a nonprofit pediatric burn rehabilitation center in Chile.

SUBJECTS

Fourteen pediatric patients with burn sequelae neuropathic pain.

OUTCOME MEASURES

Demographics, burn and pain evolution (type, intensity [using Wong-Baker FACES], and Douleur Neuropathique 4 [DN4]), and patient functionality. Plasma lidocaine levels were measured at 0, 12, 36, and 60 hours after treatment commencement.

RESULTS

Fourteen patients were evaluable for plasma lidocaine levels. Twelve patients were available for clinical assessment (two patients lost to follow-up) [mean (standard deviation)]: age, 11 years 7 months (2 years 6 months); weight, 45 kg (11.9 kg); burn evolution, 5 years 6 months (4 years); time between burn and pain onset, 3 years 6 months (3 years 2 months); time between pain onset and treatment, 5.1 months (4.8 months); lidocaine, between < and ½ plaster; initial pain intensity (FACES), 6.8 (1.6); final pain intensity, 0 in 11/12 patients; DN4, initial-6, final-2.3. All patients reported improved functionality. Plasma lidocaine levels were ≤27.45 ng/mL (>180 times below critical levels). No adverse reactions occurred.

CONCLUSIONS

These are the first published data suggesting that 5% lidocaine medicated plaster improves patient functionality, and is effective and safe for the treatment of neuropathic pain in pediatric patients with burn sequelae.

Puerarin alleviates burn-related procedural pain mediated by P2X(3) receptors

Pain is a major problem after burns. Procedural pain evoked by burn dressing changes is common in patients, and its management is a critical part of treatment in acute burn injuries. Burn pain is very likely the most difficult form of acute pain to treat. ATP contributes to inflammation, and ATP is implicated in peripheral pain signaling via actions upon P2X(3) receptors. Puerarin is extracted from a traditional Chinese medicine and may act on P2X(3) receptor mechanisms. The Visual Analogue Scale (VAS) has been shown to be a sensitive indicator of pain intensity and treatment effects. Peripheral blood mononuclear cells (PBMCs) are involved in nociception or pain after burn injury. Burn patients were randomly divided into normal saline (NS) group (salt solution is saline) and puerarin-treated group and pain (Visual Analogue Scale scores) and inflammation (PBMCs) measured. Burn pain produces a stress response, so blood glucose, insulin, and cortisol levels in burn patients were determined. Furthermore, the expression of P2X(3) protein and mRNA in PBMCs was detected. The VAS scores in the puerarin-treated group were lower than those in NS group. The blood glucose, insulin, and cortisol levels in the puerarin-treated group at post-dressing changes were significantly decreased in comparison with those in NS group. The expression levels of P2X(3) protein and mRNA in PBMCs of burn patients in NS group were significantly increased in comparison with those in the puerarin-treated group. Puerarin can antagonize inflammatory factors (such as ATP) and decrease the upregulated expressions of P2X(3) protein and mRNA in PBMCs after burns to decrease VAS. Thus, puerarin had an analgesic effect on procedural pain in dressing changes of burn patients related to P2X(3) receptors.

Employment outcomes after burn injury: a comparison of those burned at work and those burned outside of work

This study compares employment rates and barriers to return to work in subjects burned at work with those burned outside of work. Further, this study examines the influence of electrical etiology on return to work outcomes. The electronic records of burn survivors treated at a Regional Burn Center outpatient clinic from 2001 to 2007 were retrospectively reviewed. Inclusion criteria included employment at the time of burn injury and age of 18 years or older. Demographic and medical data were collected. Documentation of barriers to return to work was reviewed and classified into eight categories. Return to employment was grouped into four time intervals: 0 to 3, 3 to 6, 6 to 12, and greater than 12 months after injury. Logistic regression analysis was used to determine predictors of unemployment at greater than 1 year for subjects burned at work, outside of work, and those burned at work without electric injury. The authors identified 197 patients for inclusion in the study. Their age was 37 ± 0.8 years (mean ± SEM), and TBSA burned was 16 ± 1%. Fifty percent of subjects were burned at work. Electric etiology was seen only in those burned at work (n = 24). Forty-four percent (n = 43) of subjects injured at work remained unemployed at 1 year compared with 22% (n = 22) of subjects injured outside of work. The most frequent employment barriers included pain (72%), neurologic problems (62%), and psychiatric problems (53%) for those burned at work; and pain (63%), neurologic problems (59%), and impaired mobility (54%) for those burned outside of work. Significant predictors of unemployment at greater than 12 months included burn at work, pain, impaired mobility, other medical problems, and inpatient rehabilitation (P < .05). When the electrical injury subjects are removed from the analysis, significant predictors of unemployment at 12 months include burn at work, pain, inpatient rehabilitation, and length of stay (P < .05). Burn survivors experience multiple complex barriers in returning to work. Burn at work is a significant predictor of unemployment at 1 year even after controlling for electric etiology. Further study is required to better understand the influence of work setting on employment outcomes.

Pruritus: management algorithms and experimental therapies

Pruritus (itch) is a major symptom in many dermatologic as well as systemic diseases and has a dramatic impact on the quality of life in these patients. The symptom of itch has to be treated on the basis of its pathophysiology and its underlying disease. In daily practice, a "quick" diagnosis of the underlying disease is often difficult, although a rapid relief of the itch is desired. We often treat patients on the basis of the symptomatology. A rational therapeutic ladder for a symptomatic therapy is useful until the final diagnosis has been confirmed. There are probably many subtypes of pruritus, just as there are many diseases that cause itch. The pathophysiology in many subtypes of pruritus is still poorly understood, hindering a rapid and targeted treatment strategy. An extensive diagnostic workup is often required to determine the final cause(s) of the itch. Thus, in daily life, physicians often start with a more or less rational therapeutic strategy to combat the debilitating itch. We present possible therapeutic ladders that form the basis for effective therapeutic itch strategies in various diseases. On the basis of our current knowledge about the different pathophysiologies of itch, on clinical trials or case reports, and our own clinical experience, we aim to present therapeutic ladders for the rapid as well as long-term management of itch. Finally, we summarize current exciting developments of experimental strategies in itch research and in clinical development for itch therapy.

The impact of opioid administration on resuscitation volumes in thermally injured patients

Administration of resuscitation volumes far beyond the estimates established by burn-body weight resuscitation formulas has been well documented. The reasons behind this increase are not clear. We sought to determine if our resuscitation volumes had increased and, if so, what factors were related to their increase. A retrospective chart review identified 154 patients admitted with burns greater than 20% of their BSA during the years of 1975-1976 (period 1), 1990-1991 (period 2), and 2006-2007 (period 3). Charts were reviewed for total fluids (crystalloid, colloid, and blood products) and opioids given before admission, during the first 8 hours of treatment, the next 16 hours of treatment, and the following 24 hours of treatment. Opioids were converted to opioid equivalents (OE). Multiple regression analysis was performed to determine the effects of variables of interest and control for confounders. Significance was assumed at the P < .05 level. Resuscitation fluid volumes increased significantly among adults from 3.97 ml/kg/%BSA during the first period to 6.40 ml/kg/%BSA during the third period (P < .01). The same trend in children <30 kg was not seen (P = .72). Fluid administered during the first 24 hours was significantly associated with age, BSA, intubation, latter two study periods, and opioid administration. Fluid administration was consistently associated with opioid administration at all measured time points. At 24 hours postburn, patients who received 2 to 4 OE/kg required an average of additional 3,650 +/- 1,704 ml of fluid, those receiving 4 to 6 OE/kg had required an average of 25,154 +/- 4,386 ml, and those who received >6 OE kg had required an average of 32,969 +/- 3,982 ml. In this single center retrospective study, we have shown a statistically significant increase in resuscitation fluids (from 1975 to 2007) and an association of resuscitation volumes with opioids. Opioids have been shown to increase resuscitation volumes in critically ill patients through both central and peripheral effects on the cardiovascular system. Because increased fluid resuscitation has been associated with adverse consequences in other studies, further research on alternative pain control strategies in thermally injured patients is warranted.

Burn injury pain: the continuing challenge

The development of more effective methods of relieving pain associated with burn injury is a major unmet medical need. Not only is acute burn injury pain a source of immense suffering, but it has been linked to debilitating chronic pain and stress-related disorders. Although pain management guidelines and protocols have been developed and implemented, unrelieved moderate-to-severe pain continues to be reported after burn injury. One reason for this is that the intensity of pain associated with wound care and rehabilitation therapy, the major source of severe pain in this patient population, varies widely over the 3 phases of burn recovery, making it difficult to estimate analgesic requirements. The effects of opioids, the most commonly administered analgesics for burn injury procedural pain, are difficult to gauge over the course of burn recovery because the need for an opioid may change rapidly, resulting in the overmedication or undermedication of burn-injured patients. Understanding the mechanisms that contribute to the intensity and variability of burn injury pain over time is crucial to its proper management. We provide an overview of the types of pain associated with a burn injury, describe how these different types of pain interfere with the phases of burn recovery, and summarize pharmacologic pain management strategies across the continuum of burn care. We conclude with a discussion and suggestions for improvement. Rational management, based on the underlying mechanisms that contribute to the intensity and variability of burn injury pain, is in its infancy. The paucity of information highlights the need for research that explores and advances the identification of mechanisms of acute and chronic burn injury pain.

PERSPECTIVE

Researchers continue to report that burn pain is undertreated. This review examines burn injury pain management across the phases of burn recovery, emphasizing 3 types of pain that require separate assessment and management. It provides insights and suggestions for future research directions to address this significant clinical problem.