Fibromyalgia syndrome (FMS) is a major clinical problem in adults and has been diagnosed in 3.5% of women and 0.5% of men in the US, representing ∼5 million persons and total annual health care costs exceeding $16 billion (1, 2). Although FMS is known to cause significant morbidity in adults, its impact in the pediatric population has only recently been addressed. Previous studies have revealed that many children continue to experience persistent pain many years after being diagnosed with juvenile primary FMS (JPFMS) (3), and that 28% of adult patients with FMS reported that their pain symptoms began in childhood (4). Perhaps if the specific interactions between physiologic and psychological factors were better understood, the developmental course of the syndrome, including possible trajectories from childhood to adulthood, could be influenced to minimize the durability and pervasiveness of its effects.
It is generally recognized that JPFMS is similar to FMS in that it is a pain amplification syndrome that includes musculoskeletal discomfort in predictable tender points, as well as sleep disturbance, fatigue, and mood problems (5). In adults, FMS is a major cause of work disability, and in children, JPFMS often causes considerable school absenteeism. In light of this constellation of symptoms, and the fact that no objective physical findings (e.g., joint inflammation) are associated with FMS, questions arise about the authenticity of the syndrome and whether FMS and JPFMS are truly rheumatic disorders (6).
The Cartesian dichotomy of pain being either in the mind or in the body is inaccurate, because chronic pain is a complex entity requiring a psychobiologic perspective that includes an array of psychological, social, and biologic factors that impact on mechanisms of pain transmission and pain modulation (7). Lifespan developmental models of chronic pain have been used to observe biologic changes over time, as well as factors such as temperament, stressor load, and family environment (8). Such a model is quite consistent with the gate control theory of pain, because it provides a framework through which a broad range of factors may be unified to define a pain response (9). For example, individual differences in temperament (usually described as a psychological variable) are apparent in autonomic nervous system functioning, hypothalamic–pituitary–adrenal (HPA) axis activation, and central processing (usually conceptualized as physiologic variables), all of which affect pain (10–12).
The aim of this study was to investigate specific psychobiologic factors that might contribute to pain amplification responses that typify the onset and maintenance of JPFMS. It was hypothesized that in comparison with children with arthritis and healthy controls, patients with JPFMS would have increased perceptual sensitivity to pain and other stimuli, heightened physiologic responses to stress, a specific cluster of temperamental features that minimize pain inhibition, greater affective symptomatology, poorer parental psychological adjustment, and increased family conflict.
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- PATIENTS AND METHODS
The purpose of this study was to describe key psychobiologic elements that differentiate between children with JPFMS, children with arthritis, and healthy controls. Results showed that compared with children with arthritis and control subjects, children with JPFMS demonstrated significantly greater temperamental instability, as evidenced by significantly lower mood, irregularity of daily habits, low task orientation, and high distractibility. Furthermore, children with JPFMS had greater levels of anxiety and depression than did children in the other groups, resulting in an interesting triangle of temperamental factors, affective responses, and chronic pain. Although these 3 sets of factors interact, it is very difficult to demonstrate specific antecedent–consequence or causal relationships.
Temperamental characteristics are stable essentially from birth and have been shown to affect multiple areas associated with adaptive or maladaptive functioning (28, 29). For example, temperamental style impacts on coping with stressors (30), including an individual's response to invasive procedures and postoperative pain (31–34). Thus, it is very likely that specific temperamental factors antecede the manifestation of problematic pain syndromes. The fact that children with JPFMS reported higher levels of anhedonia and ineffectiveness, however, raises questions about the specific sequence of events in the development of the observed triad. Thus, temperament could a) be the common element that underlies poor psychological adjustment and difficulties coping with pain, b) principally affect psychological adjustment, which then impacts on coping with chronic pain, or c) sensitize an individual to pain responses, thereby taxing coping and affecting psychological adjustment. Only through prospective longitudinal studies may we determine which factors are primary and which serve as mediating variables leading to other problematic outcomes.
Previously reported data on the prevalence of psychopathology among children and adolescents with JPFMS have been inconsistent. Reid et al (35) observed no significant group differences in psychological functioning between patients with JPFMS, those with arthritis, and healthy controls or their parents, while Yunus and Masi (36) and Mikkelsson et al (37) reported relatively high rates of psychopathology in pediatric patients with JPFMS. Data from the present study are consistent with those from latter studies and may even represent somewhat of an underestimate of true effects, given that some of the patients with JPFMS were receiving antidepressant medication to facilitate sleep and pain relief. Further systematic studies controlling for relevant variables are needed to identify cause–effect relationships.
Parental and familial influences provide important contextual information but potentially cloud the picture even more. Parents of children with JPFMS demonstrated higher levels of anxiety and depression, as well as poorer psychological adjustment overall, compared with parents of children with arthritis and parents of healthy control subjects. Whether this is in response to dealing with a child experiencing chronic pain or whether parental anxiety and depression antecede a child's difficulties has not been shown. Similarly, results from the current study show that families of children with JPFMS function more poorly compared with other families (i.e., cohesion and organization are diminished and conflict is increased), corroborating data from a previous study (38). The question remains as to whether maladaptive families produce children with problematic pain syndromes or whether such syndromes are extremely disruptive and help break down family systems.
An interesting question focuses on the manner in which ontogenetic and environmental factors affect children's specific pain experiences. In this study, patients with JPFMS demonstrated significantly greater perceptual sensitivity and more symptom reporting, as well as higher total pain sensitivity levels, than did the other subjects. Parents of children with JPFMS reported that the level of pain sensitivity in their children was greater than that reported by parents of children in the other groups. Although such characteristic pain responses have been linked to coping with acute pain (39), the present findings are unique in that clear differences in pain responsiveness were shown for children with chronic pain syndromes.
We had hypothesized that basic physiologic reactions to stressful events would be different between the 3 groups, thereby further supporting the notion that psychological and physiologic stress and pain responses are inextricably related. However, differences between the 3 groups in cortisol levels before and after venipuncture were not significant. The lack of difference may be attributable to methodology, because the situation may not have been sufficiently stressful for any of the subjects to mount a major response. In addition, initial saliva samples were gathered just before venipuncture; these 2 events may have been too temporally proximate, in which case the stress response was already launched. Finally, factors such as circadian rhythm (27) and individuals' baseline responsiveness (40) may have a major impact on salivary cortisol levels, and such factors were not considered in the present study.
The present study has other limitations. Although the sample size provided enough power to show group differences, it was not sufficient to conduct the multivariate analyses needed to delineate specific relationships among variables within the groups. Given the relatively low prevalence of pediatric FMS, multicenter studies would be needed. The current research sample comprised white families. Although the incidence of JPFMS and arthritis is higher in whites than in nonwhites (35), and the racial distribution in the current study was relatively consistent with the epidemiology of specific rheumatologic illnesses, the contribution of ethnic, sociocultural, and socioeconomic factors could not be appreciated. This limits the generalizability of our findings.
With any cross-sectional study design, it is impossible to demonstrate directionality or infer causality. The causal relationship between temperament, pain sensitivity, and psychological and family functioning is impossible to determine without using longitudinal data. The ideal methodology would involve following up a cohort of children over a period of years so that antecedent and consequent relationships in this complicated model may be identified.
Finally, it is difficult to assess the impact of prescription medications on self-report measures and salivary cortisol levels. Due to the nature of JPFMS and arthritis, dosages and medications change frequently. In addition, subjects reported that they either were taking the medication infrequently or were not taking it at all at the time when saliva was collected for measurement of cortisol. To truly account for medication effects, one would have to track specific usage over a period of time, which was not done in the present study.
The current study offers support for a psychobiologic model with factors that interact to place a child at increased risk of developing a pain disorder. Interventions should target the identified risk factors, such as augmenting a child's ability to cope with pain and increasing his or her daily activities (41). Reports from preliminary studies of children with JPFMS (42–44) and adults with FMS (45, 46) have suggested that cognitive–behavioral treatments, with emphasis on self-regulatory strategies and pain perception, are effective. The findings of this study, combined with results of previous studies, suggest that interventions to enhance coping and adjustment in children with JPFMS might best include both children and their parents. Family therapy may facilitate a reduction in family conflict, as well as an increase in cohesion and organization. Specifically, an increase in family cohesion might function as a protective factor for those children at risk for psychological adjustment problems.
The ultimate goal of research on chronic pain syndromes in both children and adults is to account for the array of physiologic and psychological variables that come into play, and to integrate them into a holistic model that may be applied to both research and clinical paradigms. Data from the present study make it clear that a constellation of stable individual differences in temperament, social/ecologic variables (e.g., parental and family characteristics), and pain reactivity are all linked in manners yet to be defined. Nonetheless, these and other factors should be pursued, both in the clinical setting and in basic and applied research.