Chronic pain in children and adolescents (hereafter called children) is common, but the group is heterogeneous. Many children appear to cope well with chronic pain in daily life, wereas for others, pain is associated with high impact on a wide range of areas such as school attendance, physical and social activities, family functioning and psychological well-being (1–3). The latter has been referred to as “high impact chronic pain” (HICP) (4, 5). To assess functioning in chronic pain, a biopsychosocial approach is recommended in international studies and guidelines, emphasizing the interplay among biological, psychological, and social factors (3, 6, 7). This approach also forms the basis of interdisciplinary pain rehabilitation (IPR), grounded in a cognitive behavioral framework, which is the recommended treatment strategy for children with chronic pain (3).

IPR is typically provided in specialized pediatric pain clinics. However, access remains limited, and long geographical distances further restrict availability in countries such as Sweden (8, 9). This may lead to inadequate care and increase the risk that the pain persists into adulthood with limitations in physical and social activities, vocational ability and mental health (10–15). IPR is also resource-intensive and expensive in terms of personnel and treatment time (16). Consequently, children with more severe and complex symptoms, classified as having HICP, should be prioritized for IPR, and their specific needs and contributing factors must be clearly identified.

Previous studies on HICP in adults and children have mostly relied on pain intensity and pain interference for classification purposes (4, 5, 17–20), leaving an opportunity to adopt a broader biopsychosocial perspective that more fully captures the complexity of symptoms in children. In addition, the characteristics or clinical factors that contribute to HICP are not well investigated in children (4, 21, 22). For instance, studies including parental or behavioral aspects are lacking. These aspects need to be investigated in greater detail to enable tailored rehabilitation going forward.

To remedy the identified research gaps, the first aim of this study is to define HICP in children from a broader biopsychosocial perspective covering physical, psychological and social aspects, and including core outcome variables for pediatric pain studies (23, 24). The second aim is to investigate characteristics and clinical factors in children and their parents as potential factors associated with HICP as indicated by pain severity, pain interference, overall well-being, sleep disturbance and school absence.

The aims of the present exploratory study were to define HICP from a wider biopsychosocial perspective and to investigate characteristics and clinical factors in children and parents as variables associated with HICP, as indicated by pain severity, pain interference, overall well-being, sleep disturbance and school absence. The major findings were that symptoms of depression and psychological inflexibility in children, as well as pain reactivity in parents were associated with HICP. Several sociodemographic and pain-related factors in children and parents differed between the groups of children with high and low impact chronic pain.

This study adds to the very few studies investigating HICP in children (4, 17, 18). Previous studies have used a limited and narrower definition of HICP, leaving out psychosocial aspects of the biopsychosocial model in their classification attempts (4, 5, 17–20). As a result, these approaches do not fully reflect the biopsychosocial principles emphasized in current international pediatric chronic pain guidelines (3, 55). Neither parental nor behavioral aspects have been included, making the present study unique, as both variables have been described as important factors for the development of chronic pain (56). Our proposed definition builds upon previous conceptualizations of HICP, integrating all components of the biopsychosocial model and encompassing the recommended mandatory and key outcome domains for pediatric chronic pain research that are relevant to baseline assessment (24). In doing so, we align with existing international guidelines while further refining the assessment of high impact chronic pain in children. This approach resonates with the biopsychosocial principles emphasized in contemporary frameworks such as the WHO guidelines, the Lancet Child & Adolescent Health Commission, the European Pain Federation (EFIC) pain recommendations, and the IASP/ Special Interest Group (SIG) on pediatric pain statements (3, 55, 57, 58). By incorporating these perspectives, our definition not only reflects current best practice but also advances the conceptualization of HICP in pediatric populations.

Children with complex symptoms should be managed in tertiary care, a recommendation supported by our findings, as the majority (59.7%) were classified as having HICP. A similar proportion (63%) was reported in a German tertiary care study (18), which contrasts sharply with school-based studies where only 5%–10% of children were identified as having HICP, likely due to differences in population severity and assessment context. School samples represent the general population with mostly mild pain, whereas tertiary care should include the moste severe and complex cases (4, 17).

All participants had experienced pain for more than three months, consistent with the International Association for the Study of Pain (IASP) definition of chronic pain. It could be hypothesized that a longer duration of pain would be associated with greater impairment in daily functioning. However, our analyses revealed no apperent difference between the HICP and LICP groups with respect to the mean duration of pain prior to assessment. These findings suggest that pain duration alone is unlikely to account for the greater impact on daily life observed among children with high impact chronic pain.

When investigating child-related variables associated with HICP, only higher levels of depressive symptoms and psychological inflexibility turned out significant. Depression is together with anxiety the most common psychiatric comorbidity in children with chronic pain (59–61) with a prevalence which is more than three times higher than in the general population (62). Previous studies have shown relations between psychiatric comorbidity and increased pain, poorer quality of life, and reduced functioning in everyday life (63–67), as well as an increased risk of continued problems into adulthood (14). This underscores the critical role of depressive symptoms in HICP and highlights the necessity of addressing mental health within pediatric chronic pain treatment, particularly in tertiary care settings (3, 62, 64, 68). One treatment strategy with proven effect for depression is Cognitive behavioral therapy (CBT). Since this treatment paradigm is the most used within chronic pain treatment, CBT strategies to specifically target depression could easily be integrated in IPR (69) or possibly used outside specialized pain care to prevent HICP (68).

As mentioned earlier, higher baseline values of psychological inflexibility (consisting of items assessing pain avoidance and cognitive fusion) were associated with HICP in this study. This finding is important for the choice of interventions in the rehabilitation of children with chronic pain. Psychological flexibility is about acting in line with one's chosen values in the presence of unwanted thoughts, emotions or bodily symptoms. While psychological flexibility promotes resilience and action, psychological inflexibility captures opposite processes such as behavioral avoidance, restriction and inactivity (51). Acceptance and Commitment Therapy (ACT) is a treatment focusing on wellbeing and valued activity through heightened psychological flexibility (70). The findings in the present study are in agreement with earlier studies in adults with chronic pain, where psychological inflexibility has been shown to predict worse treatment outcomes (71, 72). Specific screening and intensive targeting of psychological inflexibility using treatment strategies from ACT during treatment may be beneficial for individuals with HICP.

Psychological flexibility in parents, as assessed by PPFQ, has repeatedly been found to be negatively correlated to child functioning in earlier studies (52, 54), but no significant difference was found in the present study when comparing groups of high and low impact chronic pain. This in contrast to the finding regarding psychological inflexibility in children.

When examining parent-related variables associated with HICP, only pain reactivity, specifically parental worry about the child's pain, was significant. Such parental responses may influence the child's psychological flexibility, potentially reinforcing maladaptive coping pattern (54). This finding is also consistent with the fear-avoidance model, a CBT-based framework for chronic pain with strong empirical support. The model emphasizes pain-related worry, captured in this study, as well as catastrophizing and avoidance behaviors, which have been extensively documented in adults (51, 73). This model is also applicable for children, but in such instances, it needs to be contextual and reflect the interaction between children and parents (74, 75). Parents' reactions such as catastrophizing, worrying and protective behavior with regard to the child's pain have been shown to have a negative impact on the child's reactions and to trigger avoidance behaviors in relation to pain (75–77). The findings of this study underscore the importance of interventions that address parental responses, such as pain reactivity, in the rehabilitation of children with chronic pain.

The strengths of this study include its large sample size (484 participants), the breadth of variables examined, and the inclusion of parental factors in a real-world clinical setting, as all children aged 10 years or older admitted for assessment at the SPPC were included. However, the findings should be interpreted in light of certain limitations. In accordance with the STROBE guidelines, no significance tests were performed to describe differences in characteristics between the HICP and LICP groups in Table 1.

Another limitation is the retrospective design and registry data which obviously only allow for cross-sectional and no causality analyses. While we can anticipate that the associated factors, such as symptoms of depression, greater psychological inflexibility, and/or parental pain reactivity, may contribute to an escalation in pain impact, they could equally be consequences of high pain-related interference in daily life. Although we believe these factors play a role in the maintenance of pain, this conclusion cannot be drawn from the present data. Future research is needed to investigate these relationships further.

The cut-off values used to define HICP in this study were primarily informed by prior literature. However, we acknowledge that a more robust justification is warranted. In this exploratory study, no sensitivity analyses were conducted to test alternative thresholds. Further studies should focus on validating the selected variables and their corresponding cut-offs to strengthen reliability and generalizability.

The participants were all attending a specialized pediatric pain clinic, and the results cannot be generalized to children with chronic pain in other clinical contexts. As in most studies, the majority of parents accompanying their child to the clinic were mothers, which may have influenced findings related to parental factors and underscores the importance of including fathers in future research. Self-report data from questionnaires were used to identify symptoms of depression which is not sufficient as a diagnostic tool and self-report scales can only provide a provisional diagnosis.

The suggested core outcome set of measures for pediatric pain studies was followed as far as possible (24). However, because not all recommended questionnaires are translated and validated for children in Swedish, a few non-validated questionnaires were used, e.g., the PRS. However, it is commonly used and has been proven sufficient in capturing pain-related reactions (46, 78). The PIPS, which was used to assess psychological inflexibility in the participating children, has demonstrated acceptable validity and reliability in children and adults (47–50). Still, the representativity of the total score as a measure of all aspects of psychological (in)flexibility has been questioned in some studies (48, 79). Another limitation is the risk of bias, since the pain physician involved in the assessment was also the first author of the present study.

Given the high costs and limited availability of IPR, it is crucial to further investigate which children truly benefit from this intervention. Additionally, the subgroup classified as having LICP warrants closer examination to better understand their needs. This group may include at least two distinct subcategories: one that could benefit from support within primary care, and another that may require only clear explanations, reassurance, and self-management strategies. Gaining a better understanding could help optimize the use of resources and ensure that children are directed to the most appropriate care pathways.

In conclusion, further development of the definition of HICP is proposed using a broader biopsychosocial perspective to more fully capture the complexity of these symptoms. This study also highlight symptoms of depression and psychological inflexibility in children, as well as parental pain reactivity, as associated with HICP. These findings underscore the importance of taking psychiatric comorbidity and child and parental behavioral aspects into account when tailoring interventions for children with chronic pain. Specific assessment and targeting of depressive symptoms and psychological inflexibility in children, and pain reactivity in parents, during pain rehabilitation may improve treatment results in terms of functioning and reduce the risk of ongoing challenges into adulthood, especially in individuals with HICP.