How Do We Treat Children with Anterior Cutaneous Nerve Entrapment Syndrome and Is the Biopsychosocial Model Also Being Applied? A Scoping Review

Background Evidence-based guidelines for managing anterior cutaneous nerve entrapment syndrome (ACNES) in children are absent. The primary aim of this review was to scrutinize the evidence supporting currently used treatment interventions. In accordance with the World Health Organization (WHO) guidelines for managing chronic pain in children, these patients and their families and caregivers should be treated within the context of the biopsychosocial model; pain should not be treated purely as a biomedical problem. Therefore, our second aim was to evaluate whether these interventions are applied within the context of the biopsychosocial model, utilizing an inter- or multidisciplinary approach. Materials and Methods A scoping review of the literature was conducted to explore treatment strategies for ACNES in children. To ensure a comprehensive overview of published literature on this topic, the search was not restricted based on study type. Two reviewers independently assessed titles and abstracts. After excluding records unrelated to children, full texts were screened for inclusion. Any discrepancies in judgement were resolved through discussion with a third reviewer. Results Out of 35 relevant titles, 22 were included in this review. Only 4 articles provided information on long-term outcomes. The overall quality of the review was deemed low. The majority of reports did not address treatment or education within the psychological and social domains. A structural qualitative analysis was not feasible due to the substantial heterogeneity of the data. Conclusion The evidence supporting current treatment strategies in children with ACNES is of low quality. More research is needed to establish an evidence-based treatment algorithm for patients with this challenging pain problem. In line with the WHO recommendation, greater emphasis should be placed on a biopsychosocial approach. The ultimate goal should be the development of a generic treatment algorithm outlining an approach to ACNES applicable to all professionals involved.


Introduction
Chronic recurrent abdominal pain is a prevalent issue in the paediatric population, presenting a wide-ranging diferential diagnosis.Only 5-10% of these patients exhibit an underlying physical cause [1].When no underlying cause is identifed, the condition is termed functional abdominal pain.Functional abdominal pain disorders are very common disorders in children, afecting 25% of all infants and children [2].
Anterior cutaneous nerve entrapment syndrome (ACNES) is a pain syndrome characterized by localized abdominal pain resulting from the entrapment of the terminal branches of the intercostal nerves penetrating the muscle sheet of the rectus abdominis.In cases of unilateral chronic or recurrent abdominal pain without an organic explanation, consideration of this diagnosis is warranted, based on specifc criteria [3].Although ACNES was initially described in 1926 by Carnett and Bates [4], it is only in the last decade that this syndrome has been increasingly recognized in children.A notable proportion of adolescents with abdominal pain can now be diagnosed with ACNES [5].
Te body of literature describing interventions for the treatment of ACNES, including in children, is expanding rapidly.Various treatment strategies are available, encompassing conservative approaches, invasive treatments involving injections of local anesthetics, and surgical procedures to release the entrapped nerve.Markus et al. conducted a review on the efcacy of neurectomy and trigger point injections in children [6].Other authors have presented various techniques for peripheral nerve blocks, such as transversus abdominal plane (TAP) block [7][8][9][10].Despite the multitude of patients undergoing treatment for ACNES, there is a notable absence of evidence-based guidelines on how to manage these cases.Most previous publications focus on interventions involving injections and/or surgery.While some reports show promise, the critical question remains: are these treatments superior to conservative approaches and are they applied within the appropriate context?Chronic pain in children represents a signifcant health concern that often disrupts daily life, leading to school absenteeism and diminished participation in social activities, thereby impacting their social and emotional development [11].Te treatment of chronic pain in children is complex and often challenging.In addition to addressing underlying organspecifc issues, the central focus in treating abdominal pain involves the rehabilitation of normal daily life.Tis includes restoring regular meal times, promoting daily exercise and physical activity, and fostering healthy sleep patterns [11].Extensive evidence supports a multimodal approach in addressing chronic pain in children [11][12][13].Te development of chronic pain in children involves biological, psychological, genetic, and social factors, all of which should be considered in the diagnosis and treatment of chronic pain [11,14,15].In accordance with the World Health Organization (WHO) guidelines for managing chronic pain in children, these patients and their families and caregivers should be treated within the context of the biopsychosocial model; pain should not be treated exclusively as a purely biomedical problem [16].
With this review, our objectives were to address the following questions: (1) What is the evidence supporting currently used treatment interventions for ACNES in children?(2) Are these interventions applied within the context of the biopsychosocial model, utilizing an inter-or multidisciplinary approach?

Materials and Methods
Te methods in this scoping review are described based on the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) checklist [17] and the PRISMA-S Two reviewers (AT and MD) independently screened titles and abstracts.After excluding records unrelated to children, full texts were reviewed for inclusion.Any discrepancies in judgement were resolved through discussion with a third reviewer (BdM).

Results
With this search, we identifed 476 reports (see Figure 1).After removing 217 duplicates, we screened abstracts and titles, discarding 224 as these pertained to adults.Four reports were excluded due to unavailability of full text.Upon reading of the articles, one more was excluded because it also involved adult patients.Six reports were excluded as they did not study any intervention or treatment and one because the patient had a diferent diagnosis.In total, we reviewed 23 publications.A systematic review encompassing six studies was identifed.However, since these six studies were already included in this review, the additional review was not incorporated into the data [6].Another report initially appeared to be a review but was, in fact, a prospective observational study assessing the predictive value of a questionnaire [20].A structural qualitative analysis was not feasible due to the strong heterogeneity of the data.
Five case series (300 patients) and nine case reports (19 patients) reported on injections with local anesthetics.Additionally, fve case series (108 patients) and two case reports (2 patients) reported on surgical procedures, and one 2 Pain Research and Management study detailed outcomes after both injections and surgical interventions (12 patients).Only one article described the results of conservative noninvasive treatment [21].Among the 11 case series, six originate from the same surgical research group, accounting for 74% of all patients [5,20,[22][23][24][25].Furthermore, some articles may have overlapping patient populations [7,22,23,26].

Results for Injections with Local Anesthetics.
Local anesthetics were injected using diferent techniques: rectus sheath block, TAP block, or trigger point infltration, with or without the aid of ultrasound.No comparative studies have been conducted on the technique, the use of ultrasound, or the addition of steroids.Most studies utilized local anesthetics combined with steroids.Te median number of injections ranged from 1 to 2, administered at variable time intervals.Reported success rates ranged signifcantly from 38% to 100% (see Table 1).

Results for Surgical Intervention.
Te predominantly reported surgical intervention was primarily anterior neurectomy, demonstrating a success rate ranging from 57% to 100%, with a reoperation rate of 25% [5,22,[25][26][27].Additionally, one report described laparoscopic resection of the proximal nerve segment following an unsuccessful anterior neurectomy [27].Details regarding preoperative treatments were not always clear in these publications.Occasionally, patients received paracetamol, nonsteroidal anti-infammatory drugs, opioids, and/or antineuropathic medication prior to consultation with the surgeon, but information about medication was not consistently available.All authors report that injections of local anesthetics were administered prior to surgery, either though ultrasound-guided TAP block, rectus sheath block, or trigger point infltration.Te duration of pain symptoms before surgery varied from 6 to 15 (8-29) months across cases (see Table 2).Seven of the twenty patients (35%) reported improvement after oral medication, while one patient reported spontaneous improvement.Five patients received injections.Two of these fve were referred to surgery, but pain was resolved before surgical intervention was done.

Results concerning Psychological or Social Factors.
Among the 22 studies reviewed, three addressed the social impact of pain, specifcally in terms of school absenteeism or limitations in sports activities, afecting 90% of the patients.Five of the 22 studies reported psychiatric or psychological issues in 30% of patients.None of the studies provided commentary about psychologic treatment or physiotherapy.

Discussion
Tis literature search aimed to evaluate the evidence regarding treatment interventions for ACNES in children.Surprisingly, the majority of publications focused exclusively on invasive interventions, all of which were observational studies lacking a control group.Consequently, the overall value of evidence is deemed low.Furthermore, hardly any of these publications addressed biopsychosocial factors or treatment options from a biopsychosocial perspective.Treatment strategies should be tailored to individual patient needs, considering the presence of psychological comorbidities.Nonpharmacological measures, such as cognitive behavior therapy, hypnotherapy, and guided imaginary, have shown efcacy in managing chronic abdominal pain in children and could be viable options [28][29][30].
Pain education is also deemed crucial in this patient category [29].Te incidence of chronic pain in children is increasing [11], and the body of evidence supporting the value of nonpharmacologic treatments is expanding [31].Tis review specifcally explores the published treatment options and evaluates their merit.
While the literature on the treatment of ACNES in children is expanding, it predominantly consists of case reports.Te methodologic quality of these publications tends to be low.Despite another review claiming level II evidence, we disagree, as there were no randomized controlled trials or meta-analyses and a lack of case-control studies [6].All six studies were observational nonblinded studies, thus prone to bias.
Te existing literature predominantly reports two treatment strategies for managing ACNES in children: injections with local anesthetic (with or without steroids) and surgical procedures.All but one of the relevant publications concern invasive treatments.Te only exception is a publication reporting the outcome of conservative treatment in 20 patients, of whom 5 required injections and ultimately none of them needed surgical intervention [21].Tis specifc study demonstrated that conservative strategies can also be efective.
Most of the publications on injection techniques pertained to either rectus sheath block or trigger point infltration.Te reported success rates ranged from 38% to 100%.Although Bairdain et al. [7] primarily aimed to report surgical outcome, they revealed that all 48 patients received repeated TAP blocks before surgery.Nine of those eventually required surgery, indicating a success rate of 81% with TAP block.While the article did not specifcally address whether alternative treatments were pursued or needed, the fndings suggest that surgery should only be considered after exhausting other treatment modalities.As of now, no studies have been published comparing the efectiveness of TAP block to other techniques in the treatment of ACNES.
An RCT in adults with ACNES had demonstrated the superiority of lidocaine over saline in providing immediate pain relief after trigger point injection [32].Reviewing their own previous (mainly observational) ten studies encompassing a total of 834 patients, the same research group estimated that ten percent of the patients experienced sustained pain relief following a single lidocaine injection [33].While local injections often incorporate steroids, their efcacy in the context of chronic pain remains a topic of debate.A study involving adults in a postoperative setting evidently demonstrated the value of adding steroids to a peripheral nerve block [34].For chronic pain, however, this is debatable.A study by Mol et al. in adults indicated no discernible beneft of adding steroids to lidocaine injections for ACNES [35].
In another study involving adult patients, Jacobs et al. found that the free hand technique was comparable to the ultrasound-guided technique for trigger point injections [36].Tere is a lack of corresponding data in children.
In the context of surgical treatment for children with ACNES, anterior neurectomy emerged as the predominant approach.Te duration of preoperative pain symptoms as well as the type of conservative treatment given before surgery exhibited variability.Preoperative interventions lacked standardization, and their specifcs were often not clear.Furthermore, a majority of studies featured limited patient cohorts and lacked reporting of long-term follow-up outcomes.Only one retrospective study involving 26 patients reported on extended postoperative outcomes, revealing a 58% success rate [26].
While the biopsychosocial model is recognized as the appropriate framework for addressing pain in children, it is remarkable that a limited number of publications address psychosocial aspects [11].Among the 22 studies included in this review, merely three explored the social repercussions of pain, such as school absenteeism or limitations in sports activities, afecting 90% of the patients.Psychiatric or psychological issues were reported on fve out of the 22 studies, impacting 30% of patients.Van Hoek et al. observed that some patients, who declined surgery after multiple trigger point injections, opted for conservative treatments such as transcutaneous electrical nerve stimulation (TENS), physiotherapy, and psychotherapy [20].Since the purpose of their study was to determine the predictive value of a questionnaire, they did not describe the outcomes of the diferent therapeutic options.Pain Research and Management Te lack of a standardized treatment algorithm for this specifc patient category contributes to a varied approach, with no conclusive evidence supporting any particular treatment choice.High-quality research is needed to underpin the development of clear guidelines for the treatment strategy of this elusive diagnosis.Furthermore, it is advisable that interventional procedures be exclusively employed in a multidisciplinary setting [37].

Conclusions
Te quality of the evidence supporting the current practice of treating ACNES in children is low.More research is needed to establish an evidence-based treatment algorithm for patients with this challenging pain problem.In line with the WHO recommendation, greater emphasis should be placed on a biopsychosocial approach.Te ultimate goal should be the development of a generic treatment algorithm outlining an approach to ACNES that is applicable to all professionals involved.It is recommended that such an algorithm be implemented within an inter-or multidisciplinary setting, taking into account the biopsychosocial model adapted to the age and social context of the children and their parents.

Table 2 :
Outcome after surgical treatment.