Fibromyalgia syndrome in adolescents is characterized by chronic widespread musculoskeletal pain and multiple associated symptoms. Consistent with prior reports [8, 9], results of this study showed that joint HM commonly co-occurs with JFM in children and adolescents with nearly half of the adolescents with JFM also having HM. This is similar to findings from adult fibromyalgia studies which have reported that 46.6%  to 62%  of fibromyalgia patients also had HM. In addition to replicating findings regarding the overlap between JFM and HM, results of this study suggest the possibility that a ‘benign’ condition like joint laxity can be associated with enhanced pain sensitivity in JFM patients. Specifically, HM+ patients show significantly greater physiologic sensitivity as measured by TP threshold and TP count than HM- patients, even though their self-report of clinical pain intensity did not differ. However, it is unclear if this difference is clinically relevant as all patients had relatively high pain sensitivity. Interestingly, all tender point locations were lower among the HM+ group and not significantly different among areas that are typically flexible (i.e. knees).
Potential mechanisms underlying the relationship between HM and pain sensitivity in JFM patients might include genetic vulnerability associated with gene polymorphisms responsible for pain perception , immunologic factors , or related to the common features of dysautonomia (syncope, orthostatic hypotension, tachycardia, etc.) often reported by both HM and JFM patients [24, 25]. Interestingly, despite the evidence of increased pain sensitivity in JFM HM+ adolescents, we found that the subjective report of clinical pain (VAS pain ratings) did not correlate with physiologic pain sensitivity. Furthermore, there was no significant difference in clinical pain reports between JFM adolescents with and without HM. These results reinforce the notion that pain is a complex subjective multidimensional experience. Results obtained from different assessment methods (subjective pain ratings versus sensory testing) may therefore represent different facets of pain.
The results of this study have implications for the measurement of pain outcomes in clinical trials of JFM. In recent studies, cognitive behavioral therapy (CBT) has been found to be a promising treatment for JFM [26, 27] and the parent clinical trial associated with this study showed that CBT was effective in reducing pain-related disability and depressive symptoms. Patients also reported reduced pain intensity (VAS) levels, but there was no change in tender point sensitivity after CBT. In order to change physiologic pain sensitivity, other types of interventions, for example, intensive aerobic exercise programs, which have been shown to be effective for pain reduction  need to be further studied. Tailored programs for JFM HM+ children focusing on joint protection and strengthening might also be investigated to see if they can produce reductions in mechanical stress which could ameliorate heightened pain sensitivity.
We recognize several limitations of our study. Our patients were recruited from tertiary pediatric rheumatology clinics; therefore, they may represent the most severe and prolonged cases of JFM. The majority of patients (85%, n = 112) had a total of >14 positive TP and nearly half (47%) had 18/18 positive TP. Another limitation is that the scoring systems for HM (i.e. Beighton, Brighton, Carter and Wilkinson) were not strictly standardized in our study; however, each rheumatologist indicated they documented hypermobility if a patient met criteria. Despite the potential recruitment of patients with more severe JFM and the non-standardized clinician assessment of HM, the prevalence of HM in this sample was found to be similar to that reported by Siegel and colleagues, i.e., almost half of the JFM sample .