3.2.1. Demographic Factors
Briefly, several demographic factors are considered in relation to pediatric chronic pain, including age, sex, and ethnicity.
Increased age (typically early adolescence rather than early childhood) is associated with various pediatric chronic pain disorders, including low back pain [
8] and musculoskeletal pain [
9]. That is, chronic pain appears to most often occur in adolescence rather than earlier in childhood. However, recurrent abdominal pain appears to peak below 5 years of age and again between ages 8–10 years [
10]. This particular finding speaks to the potential relationship between pain and developmental stage, which will be discussed later in this article.
The literature suggests that female youth report more severe headache and back pain [
11,
12,
13,
14], chronic musculoskeletal pain [
9], temporomandibular pain disorders [
15], and recurrent or functional abdominal pain than male youth [
16]. However, some studies have found only minimal support for this relationship, demonstrating small effect sizes for duration and intensity of pain for girls versus boys [
17].
A sex by age relationship has been observed in children and adolescents with chronic migraine. Based on the extant literature, chronic migraines appear to be more common in boys than girls prior to puberty [
18]. Thus, onset of migraines in boys is likely earlier than for girls. This estimate changes by the onset of puberty, and the prevalence of chronic migraines in girls is estimated to double that of boys at that stage [
18].
Race and ethnicity have rarely been the sole focus of research on pediatric chronic pain disorders, although it is well studied in adults. Briefly, studies have found the following: (1) participants of European descent were more likely to have juvenile idiopathic arthritis than children of other descent [
19]; (2) American Indian adolescents had the highest rate of recurrent headaches followed by white adolescents [
20], and Asian and Pacific Island adolescents were the least likely to experience recurrent headaches [
20]; (3) African American youths were more likely to experience a variety of pains related to temporomandibular joint disorders than their Caucasian counterparts [
21]; (4) Hispanic ethnicity was associated with higher widespread pain scores in children with acute pain, presurgical, and chronic pain [
22]; and (5) Jewish children experienced significantly more headaches than Arab children in a sample from Northern Israel [
23]. Other groups have found no significant differences among ethnic groups in samples of children with a variety of chronic pain diagnoses [
24,
25]. In addition, ethnicity did not emerge as a risk factor for disability in a study of children with chronic back pain [
26].
In sum, demographic factors including age, sex, and ethnicity evidence some support of potential risk factors for pediatric chronic pain. These variables warrant continued research in their potential as risk factors for youth. Studies that assess demographic factors in combination with other identified variables are important for improving our understanding of risk pathways.
3.2.2. Temperament
Broadly defined temperamental factors have been cited in the literature as potential risk factors [
27]. For example, infants who were more active and struggled to develop important routines were more likely to develop recurrent abdominal pain later in childhood [
28]. Children with recurrent abdominal pain were more “temperamentally difficult” than those without pain, such that girls had more of an irregular temperament style and boys were more likely to withdraw in novel situations [
29].
In a study of children with juvenile primary fibromyalgia syndrome, temperament was described as a combination between mood, daily habits, and attentional abilities [
30]. The study demonstrated that these children displayed lower mood, irregularity of daily habits, lower task orientation, and higher distractibility than a comparison group (participants had arthritis) as well as a control group [
30]. Thus, a difficult temperament may represent a mechanism by which acute pain becomes chronic and/or plays a role in maintenance of impairing pain. Temperament may also influence what eventually becomes a child’s coping style [
31], which could have important implications for the way a child responds to prolonged experience with pain. While temperament itself is not modifiable by definition, if high-risk temperamental styles are identified early on in children with pain, the first targets of intervention could focus on the development of adaptive coping strategies before pain becomes chronic. However, other factors, outlined below, may represent more promising avenues for prevention and early intervention efforts.
3.2.3. Psychological Disorders
Chronic pain has been found to be associated with a variety of psychological issues, including anxiety, depression, anger, conduct problems, and mental health issues in general.
Anxiety. Anxiety has been frequently studied as a risk factor for numerous chronic pain disorders. While the issue of causality is often cited as a problem with this area of research, a recent study demonstrated a strong temporal association, with anxiety disorders preceding reports of chronic back/neck pain, headaches, and “any chronic pain” [
32]. However, another study of predictive factors for recurrent abdominal pain in children specifically did not find such a temporal relationships [
33].
Cross-sectional studies do appear to show a somewhat consistent relationship between anxiety and chronic pain. Anxiety has been significantly associated with general musculoskeletal pain for girls [
34], migraine with aura [
35], and recurrent abdominal pain [
36,
37]. A recent study supported this finding in a general chronic pain sample and demonstrated that youth with abdominal pain reported higher overall anxiety as well as more panic-somatic symptoms relative to other pain groups [
38]. Other studies demonstrate no relationship between anxiety and pain, including studies of juvenile idiopathic arthritis [
39] and headache or abdominal pain [
40].
Sensitivity to anxiety has also been posited as a factor that contributes to the maintenance of postsurgical pain in children and adolescents [
41]. Anxiety sensitivity is defined in terms of the degree to which an individual interprets or predicts anxiety symptoms as being related to significantly harmful somatic, psychological, and/or social outcomes [
41], and was the only predictor of maintenance of or recovery from moderate/severe chronic postsurgical pain 12 months after the surgery [
41]. Anxiety, when it becomes impairing, could be considered a maladaptive response to pain, if that is indeed the order of occurrence. Longitudinal studies could lend predictive power to the current understanding of the chronicity of pain and the role of anxiety.
Depression. Depression is strongly related to anxiety [
42] and is worth examination in relation to chronic pain in its own right. Depression appears to be an important factor in pediatric chronic pain disorders. As with anxiety, the question of whether we can infer causality between depression and pain is often cited. However, a temporal relationship was found between preceding depression diagnoses and headaches or “any chronic pain” [
32]. Another study explored childhood predictors of abdominal pain in adolescents over the course of 13 years at six different time points and found that the presence of depressive symptoms in childhood (at age 12) predicted recurrent abdominal pain two years later [
16]. This finding suggests that depression may play a role in the transition from acute to chronic pain. Cross-sectional studies have also demonstrated associations between depression and irritable bowel syndrome [
43], as well as with chronic daily headache when compared to control samples [
35].
Two studies used nationally representative community samples to understand the connection between chronic pain and psychopathology in youth who are not receiving treatment for chronic pain. First, an association was found between musculoskeletal pains and depression in both boys and girls [
34]. A second study found that 16% of all adolescents are at risk for developing depression, but this risk increases to 45% when adolescents have daily pain [
44]. Studies with larger sample sizes in pediatric clinical populations are needed to further our understanding of the interplay between depression, anxiety, and pain.
Other disorders and mood problems. A small body of literature emphasizes a connection between trauma and chronic pain, primarily focusing on abuse (physical or sexual) or injury (e.g., sports injury, accident) [
45]. These studies suggest that early posttraumatic stress disorder (PTSD) or trauma-related symptoms predict later functional impairment and pain [
45]. However, more research is needed to understand the connection between trauma and pain in the pediatric population.
Other studies have highlighted issues related to anger [
46], oppositional defiant disorder and attention-deficit hyperactivity disorder [
34], conduct problems, [
47] and a broader “psychopathology” variable [
11,
48,
49,
50]. Furthermore, “negative emotions” have been identified as a risk factor of moderate quality for headache in youth [
13]. Broad terms such as “psychopathology” and “negative emotions” are likely too vague and difficult to replicate, and they may not be particularly useful in a clinical setting. Longitudinal studies will be particularly useful in guiding our understanding of the role of psychological factors in the development of chronic pain.
3.2.4. Stress
The subjective experience of stress demonstrates a strong relationship with pain. One study found that perceived stress explained a significant amount of the variance in present and worst pain intensity for younger children [
25]. For adolescents, perceived stress was associated with present pain intensity only [
25]. These findings are consistent with the adult literature on perceived stress and pain.
Houle and Nash [
51] posit that stress is a risk factor in the “chronification” of headache in adults through several mechanisms, including daily stressors and chronic hyperarousal. Stress is also posited to indirectly relate to a series of other potential variables that can impact pain, such as fear of pain, locus of control, dysregulation of sleep and eating routines, overuse of medications, and psychopathology [
51]. Thus, stress may play a crucial role in both the etiology and maintenance of pain problems. Finally, the experience of negative or stressful life events appears to be related to chronic pain [
16,
52,
53,
54]. Future research is needed to understand these complex interactions among stress and other variables as they relate to pain, especially in the pediatric population.
3.2.5. Coping Style
Compas et al. [
55] define coping as “conscious volitional efforts to regulate emotion, cognition, behavior, physiology, and the environment in response to stressful events or circumstances”. This widely accepted definition, especially as it relates to children and adolescents, takes developmental level into account, stating that an individual’s development might facilitate or hinder the type of coping strategy that is available to and/or used by the individual [
55]. Furthermore, unlike adults, children may not have developed a fully formed “coping style” or approach that they typically rely upon [
26]. Children and adolescents may be more likely to employ a larger variety of coping strategies than adults as they attempt to form their own individual coping style. Developmental stage, therefore, is important to take into consideration when designing studies. Some strategies are seen as positive or adaptive and others are seen as maladaptive.
In a study of pediatric pain patients, coping was correlated with depression and disability [
56]. The most common strategies were broken down into maladaptive (internalizing and catastrophizing) and adaptive (problem-solving and behavioral distraction) [
56]. A strong relationship was found between the maladaptive coping strategies (e.g., dependency, denial, catastrophizing) and chronic pain for adolescents, and is consistent with findings in the adult literature [
57,
58,
59,
60]. Differences in coping strategies across diagnoses have also been found [
56]. A musculoskeletal group reported greater disability and more difficulty coping than the headache group [
56]. Further support relates pain catastrophizing to pediatric chronic pain conditions [
61]. Together, these findings suggest that coping strategies represent an important area of focus for prevention and intervention strategies for chronic pain. Some promising studies, which are reviewed in depth below, have utilized more sophisticated methodology in order to improve our understanding of the role of different coping strategies.
3.2.6. Fear, Avoidance, and Beliefs
Asmundson et al. [
62] argue that fear, anxiety, and avoidance appear to play a circular role in chronic pain. An original injury or experience of pain may lead to fear, which leads to avoidance of activities that may cause more pain. Avoidance of the anxiety felt in situations where an individual might expect to feel pain may strengthen the behavioral avoidance response as well [
63]. Anxiety and avoidance may increase the fear. However, with avoidance of activity, eventual involvement in such activities is likely to involve a great deal of pain. Like a self-fulfilling prophecy, the fear of pain is confirmed, leading to continued avoidance of activities. Thus, Asmundson et al. [
62] argue that the paradoxical and cyclical nature of the fear and avoidance relationship in chronic pain is problematic.
This problematic cycle includes fear-avoidance behaviors, which have been cited as potential risk factors for adults in the transition from acute to chronic pain with musculoskeletal pain [
64], low back pain [
65], and back and neck pain [
66], as well as with maintenance of chronic pain [
67]. In addition, fear of pain on its own has been identified as a risk factor in youth [
61]. Studies such as these need to be replicated in pediatric populations to help understand these pathways in children.
A variety of specific beliefs have also been attributed to poor pain outcomes. In a controlled study of adolescents with recurrent abdominal pain (RAP), participants reported significantly greater concerns about undiagnosed physical disease and greater belief in susceptibility to functional impairment by pain and other physical symptoms [
36]. Children with recurrent abdominal pain also appear to have significant hypochondriacal beliefs [
36]. In the case of headache, locus of control and self-efficacy appear to be important risk factors [
46]. A helplessness–hopelessness factor predicted adjustment to low back pain in adults one year later [
68]. Thus, some studies support the idea that different types of negative beliefs about the self are related to chronic pain.
3.2.8. Summary
The greatest amount of evidence suggests a number of risk factors in relation to pediatric chronic pain, including difficult temperament, anxiety, depression, subjective experience of stress, passive coping strategies, and sleep problems. Some evidence suggests that fear and avoidance behaviors as well as negative beliefs about the self may be risk factors for the development and/or maintenance of pediatric chronic pain. Mixed results for increased age, female sex, and a general psychopathology variable warrant further investigation. However, as discussed, there are a number of problems with the current literature. Small sample sizes, imprecise terminology, lack of comparison studies, and correlational analyses make it difficult to generalize results to the pediatric pain population as a whole. All studies reviewed primarily utilize pain as their outcome measure as well. A second generation of research is needed to build upon this first generation that incorporates more sophisticated methodology and sound research design, examining functional ability as an additional outcome measure.