Consistent with our first main hypothesis, girls in both the chronic pain and non-clinical groups reported elevated global AS and AS physical concerns relative to their male counterparts. These findings of sex differences irrespective of clinical status held after controlling for child age and child race/ethnicity (Caucasian vs. non-Caucasian). Contrary to our second main hypothesis, children with chronic pain did not report higher global AS or AS physical concerns relative to non-clinical children. However, these findings were qualified by a significant group by sex interaction effect which indicated that girls with chronic pain reported elevated AS physical concerns relative to non-clinical girls but no such group differences for boys (see ). This interaction did not reach significance for global AS and the results of the exploratory analysis of AS social and psychological concerns did not indicate any differences based on sex or group, nor any interaction effects. Taken together, these findings indicate that AS physical concerns reflect the most salient aspect of sex-based differentiation in AS for chronic pediatric pain. Thus, girls with chronic pain evidenced greater fears of the physical consequences of anxious arousal compared to girls without chronic pain but these differences did not extend to fears of the social or psychological consequences of anxiety sensations. Boys with chronic pain did not differ from non-clinical boys with respect to any such fears of anxious arousal.
To our knowledge, this is the first study that has specifically investigated sex differences in AS among children with chronic pain and a comparison sample of non-clinical children. One prior study that did not compare boys and girls found that children with noncardiac chest pain endorsed heightened global AS as well as elevated AS physical and psychological (but not social) concerns compared to controls (24
). Our findings of elevated global AS in non-clinical girls relative to non-clinical boys agree with the results of four previous studies with non-clinical children (26
). In an earlier report, with a subset of roughly half the current non-clinical sample, we found no sex differences in global AS (36
) but this may have been due to restricted sample size or the inclusion of younger children (i.e., aged 8 years). Similarly, in a previous study in a subset of less than half the present chronic pain sample (N
= 87), we did not find any sex differences in global AS (43
), possibly due to low power. It should be noted however, that neither of our prior analyses explicitly tested for sex differences in AS physical concerns and this subscale has revealed the strongest sex-based differences in previous research (25
) as well as in the current study.
It is unclear why our findings of heightened fears of anxiety-related somatic sensations in chronic pain vs. non-clinical girls were not evident among boys. Analyses of the clinical characteristics in the pain sample indicated that girls reported shorter
duration of pain than boys, suggesting that in this respect, boys were more severely impacted than girls. On the other hand, there were no differences between boys and girls in the presence of multiple pain diagnoses or any individual pain diagnosis with the exception of fibromyalgia. Girls were more likely to present with fibromyalgia than boys and it is possible that this condition is more strongly linked with heightened AS. Fibromyalgia involves widespread pain and numerous tender points throughout the body as well as fatigue and disruptions in sleep, mood and cognition. Recent population-based estimates indicate that women are 1.64 times more likely than men to have fibromyalgia (95% CI = 1.59-1.69)(44
). It is possible that fibromyalgia, because of its diffuse nature, demonstrates a more robust association with fears of physical sensations related to anxious arousal compared to pain conditions with a more discrete focus (e.g., headaches; abdominal pain). This possibility is speculative and requires further study. Because approximately 30% of our pain sample presented with more than one pain diagnosis, comparisons between individual diagnoses on AS were not conducted.
Reasons for the observed sex differences in AS are not well-understood. One possibility is that girls are more willing to report fears compared to boys (45
). Research in twins indicates that AS is heritable in women but not in men (46
) suggesting that genetic susceptibility to AS in females may be a factor. A recent report (47
) found that for women, the more severe the AS, the more strongly it was influenced by genetic factors. In women, each of the three AS dimensions was influenced by both genetic and environmental factors. Among men, the AS dimensions were influenced by environmental but not genetic factors. Thus, the authors concluded that AS dimensions appear to arise from both dimension-specific and non-specific etiologic factors, the salience of which varied as a function of sex and severity. In accord, we recently found evidence for possible sex differentiation in routes of transgenerational transmission for AS in two studies conducted with a subset of the non-clinical sample included in this report. In the first study, we found that whereas parent AS was significantly positively associated with child AS in girls, no such parent-child AS relationship existed for boys (48
). In the second study, we found that in girls only, parent AS was positively linked with child AS, which in turn positively predicted children's experimental pain intensity (49
). These findings are consistent with the view that parent AS may operate via girls' own fear of anxious arousal to influence their responses to pain. One limitation of these findings is that the majority of parents in the two studies were mothers and an important consideration for future research is the examination of possible differences in father-daughter/son vs. mother-daughter/son AS and pain associations.
Limitations to the present findings should be mentioned. The cross-sectional nature of this work precludes any conclusions regarding causality. The current study relied on a self-report measure of AS; corroboration of the findings with behavioral measures of AS (e.g., laboratory stress tasks of anxious arousal) would increase confidence in the results. It has been reported that children with chronic pain endorse levels of anxious symptomatology comparable to that of children with clinical anxiety (4
). Thus, it is possible that the findings of sex differences in the pain sample could have been due to higher levels of anxious symptoms among girls with chronic pain. Although we did not include a measure of anxiety symptoms, additional analyses of the chronic pain sample indicated that our findings held even after we controlled for the presence of possible anxiety disorder as assessed by a clinical psychologist or child psychiatrist during the initial clinic evaluation. Although formal clinical assessment of anxiety disorder(s) was not conducted, the possible presence of an anxiety disorder was noted on the patients' chart by the evaluating psychologist or psychiatrist. Notably, there were no sex differences in the frequency of possible anxiety disorder in our pain sample. Future studies of AS in chronic pain samples should include established measures of anxious symptomatology and/or formal clinical assessment of anxiety disorders. Nevertheless, research on vulnerability characteristics for chronic pain among children is still nascent (45
) and few modifiable risk factors have been identified for the development of chronic pain and pain-related disability. Given that AS is a potentially modifiable risk factor that appears to be particularly salient among girls, these findings may point the way to sex-specific interventions targeting AS in vulnerable populations.
In sum, the findings point to heightened global fears of anxious arousal as well as elevated specific fears of the negative physical consequences of such arousal in girls with chronic pain and non-clinical girls relative to their male counterparts. Moreover, girls with chronic pain reported increased specific fears of anxiety-related physical sensations compared to non-clinical girls whereas such differences were not apparent among boys. These results indicate that specific aspects of AS focused on physical concerns are associated with the experience of chronic pain in girls but not in boys. Longitudinal studies are warranted to examine the extent to which AS may predict the development of chronic pain problems in a sex-dependent manner across adolescence and adulthood. Additional work may also examine whether interventions aimed at reducing AS prevents the development of chronic pain and/or reduces acute pain sensitivity among girls. Research on sex-specific childhood learning experiences may also shed light on the role of AS and related factors in the development of the adult female predominance in chronic pain.