Editors' Note: Rich, insightful conversations about current research go on every day in journal clubs around the world. The goal of our new Journal Club feature is to capture those discussions and air them for the broader pain community.
Thanks to Kathryn Birnie and Line Caes for submitting the second Journal Club. We are pleased to present their summary of the discussion from a pain journal club hosted by Christine Chambers’ lab at Dalhousie University and the Centre for Pediatric Pain Research, IWK Health Centre. Members of the journal club took up a recent paper from Walker and colleagues concerning childhood predictors of adolescent and adult functional gastrointestinal disorders and psychiatric comorbidities.
Birnie and Caes also submitted a number of questions to Lynn Walker, first author of the original study. Professor Walker’s responses appear in a Comment below.
Walker LS, Sherman, AL, Bruehl S, Garber J, Smith CA.
Pain. 2012 Sep;153(9):1798-806.
Presented by: Kathryn Birnie, BA (Hons), PhD student, and Line Caes, PhD, Postdoctoral Fellow, Dalhousie University and the Centre for Pediatric Pain Research, IWK Health Centre, Halifax, Nova Scotia, Canada
Journal club participants: Christine Chambers, PhD; Katelynn Boerner, BSc (Hons), PhD student; and Meghan Schinkel, BSc (Hons), PhD student, Dalhousie University and the Centre for Pediatric Pain Research, IWK Health Centre
Synopsis of paper and discussion written by: Kathryn Birnie and Line Caes
Our lab recently met to discuss the study by Lynn Walker and colleagues examining the predictive value of functional abdominal pain and adaptation profiles derived in childhood to functional gastrointestinal disorders and psychiatric comorbidities assessed in adolescence and adulthood. This study offers a critical contribution to the field. Given its rigorous methodology, the study provides strong evidence for the predictive role of childhood pain, particularly pain-related psychological factors, to long-term outcomes. Furthermore, the study considers multiple aspects of the pain experience (biological, cognitive, affective, and behavioral), and uniquely integrates both clinical and experimental outcomes.
Brief study synopsis
From a clinic-based sample of 843 pediatric patients with functional abdominal pain, the study authors used cluster analysis to identify three pain profiles derived from measures of sensory, cognitive, affective, and behavioral dimensions of pain. The three pain profiles were: high pain dysfunctional, high pain adaptive, and low pain adaptive.
An average of nine years later, 379 participants from the baseline sample participated in a follow-up interview assessing the presence of abdominal and non-abdominal chronic pain, psychiatric comorbidities, and job loss due to illness. As compared to the other two profiles, individuals who were part of the high pain dysfunctional profile in childhood were significantly more likely in adolescence/adulthood to meet criteria for functional gastrointestinal disorder (FGID), FGID with non-abdominal chronic pain, FGID with comorbid anxiety or depressive disorder, and job loss due to illness.
At follow-up, a subsample of 211 participants also completed an experimental pain task of thermal wind-up as a measure of central sensitization. Individuals in the high pain dysfunctional group showed significantly greater thermal wind-up with experimental heat at 48˚C, suggesting they were experiencing widespread effects of heightened central sensitization. Individuals in both the high and low pain adaptive profiles in childhood had similar clinical and lab-based outcomes in adolescence/adulthood.
Thoughts on the pain profiles
One of the most interesting findings was the similar long-term outcomes for both the low pain adaptive and high pain adaptive profiles. Given previous research showing poor coping even amongst individuals with low levels of pain, we were surprised not to see a low pain dysfunctional profile. While three profiles may have adequately captured the majority of the sample, why were no children classified into a low pain dysfunctional profile? Perhaps this is a function of selecting a clinic-based sample (i.e., that families with children who have low pain and dysfunction may seek treatment in alternate settings, rather than in a GI clinic?).
We also noted the interesting differences between profiles relating to sex and child age. The high pain dysfunctional group was predominantly female (70 percent) as compared with the high pain adaptive (63 percent female) and the low pain adaptive (50 percent female) groups. This finding may not be surprising given higher rates of recurrent pain observed amongst girls than boys (Stanford et al., 2008). The low pain adaptive profile was also significantly younger as compared to the other two profiles. Given research showing that sex and anxiety/depression influenced children’s recurrent pain over childhood and adolescence (Stanford et al., 2008), we wondered whether these sex differences would become more pronounced over time (e.g., do girls follow a different trajectory than boys?). Although an age range was not provided for participants at baseline, we also wondered about the influence of pubertal status on children’s pain and adaptation, given the many biological and psychological changes that occur during that time.
This leads to another key area for discussion, which is the role of parents and the family on the children’s pain experience. We know that chronic pain tends to aggregate within families (Saunders et al., 2007), and that parents strongly influence their children’s coping with pain (Claar et al., 2010) and functional disability (Gauntlett-Gilbert and Eccleston, 2007). Additionally, they play a key role in helping their children to seek treatment for experienced pain. Although parent-report measures of children’s coping were used to validate baseline profiles, we wondered about further consideration of parent factors in the development and trajectory of the various pain profiles. For example, parents’ own chronic pain status, parental responses to children’s pain (e.g., protectiveness), parents’ psychological distress, and beliefs about the child’s ability to cope.
The high pain dysfunctional group was characteristically identified by a number of cognitive, affective, and behavioral dimensions of pain (e.g., high pain catastrophizing, negative affect, and activity impairment). What remains unclear is whether a dysfunctional coping style developed in response to the experience of chronic pain, or whether aspects of the dysfunctional profile preceded the development of chronic pain. For example, could individuals who are at higher risk of falling into the high pain dysfunctional profile be identified by cognitive factors prior to the onset of chronic pain?
According to a recent systematic review (King et al., 2011), 4-11 percent of children and adolescents experience multiple chronic pains (e.g., abdominal pain, headache, musculoskeletal pain). Our group wondered about the application of these pain profiles to children and adolescents with multiple pains, or to those with other types of chronic pain, such as recurrent headaches.
Taking a lifespan approach
Our group commends the researchers for this critical contribution! Very few studies longitudinally examine outcomes in adulthood for children with chronic pain—fewer still, using characteristics measured during childhood to predict these outcomes.
Often, the pediatric and adult pain literatures are disconnected, treating pain in childhood as separate from pain in adulthood. While childhood may offer unique influences on the pain experience, many children with chronic pain will become adults with chronic pain. Furthermore, individual pain coping style begins forming during childhood. Altogether, this suggests that our understanding of pain would greatly benefit from more investigations such as this, taking a lifespan approach. However, we would be remiss not to acknowledge the resource-intensive nature of such longitudinal investigations.
Our group speculated about the stability of the three pain profiles identified during childhood. Given the effectiveness of various treatments for pain, we can assume (hope!) that some participants experienced a reduction in pain severity and/or developed a more adaptive coping style over time. This suggests the possibility that individuals could change pain profiles. Unfortunately, the study authors could not examine the stability of the profiles, as they did not reassess the variables used to derive the profiles at follow-up (e.g., pain beliefs, pain catastrophizing). Even if the authors had wished to do this, practically, it would have been difficult to achieve. Many of the measures used in pediatric samples are not available or appropriate for use in adult samples, and vice versa. This offers yet another challenge for the field to overcome in moving toward a lifespan approach.
Considering central sensitization
This study was very innovative in its integration of clinical and experimental methodologies. We were particularly intrigued by the use of a lab-based pain task as a measure of central sensitization.
Our group discussed how a baseline measure of central sensitization would have been very valuable. Is it possible that baseline differences in central sensitization account for the differences found at follow-up between the high pain dysfunctional group and the two adaptive pain profiles? How would the interpretation of the findings be different if baseline differences in central sensitization were found? The results are interpreted in the paper with the assumption that there would have been no initial differences at baseline, but there very well could have been.
We also wondered about the role of early infant pain experiences on differences in central sensitization and later development of chronic pain. Although not measured in the current study, participant birth status (i.e., prematurity) or NICU exposure would likely play a role in differences in central sensitization.
Lastly, we speculated about the potential role of the central sensitization findings for predicting cluster stability.
We look forward to hearing from others with their thoughts!