Widespread pain, a common feature among many chronic disorders, is thought to be caused by an underlying disease that triggers a state of central sensitization — where patients develop pain hypersensitivity because of repeated pain episodes.
“However, this argument is currently limited by evidence that has not sufficiently captured the temporal nature of the relationship between diagnosis of the underlying disease and onset of widespread pain,” the investigators wrote.
In this study, a group of researchers from Sweden’s Lund University set out to evaluate whether patients with RA, endometriosis, or IBD are more likely to develop fibromyalgia or chronic widespread pain later in their lives.
The population-based cohort study was based on patient records pooled from the Swedish Skåne Healthcare Register of healthcare consultation. Medical records were used to identify patients who had been diagnosed with RA, endometriosis, IBD, fibromyalgia, and chronic widespread pain between 2007 and 2016.
Statistical analyses were used to calculate the incidence rate ratios (IRRs), or the relative risk, for fibromyalgia and chronic widespread pain in all patient groups. IRRs were normalized for patients’ age, sex, education, and likelihood of seeking healthcare support.
Patients with RA were used as positive controls for the association between a chronic disease and higher risk of fibromyalgia and/or chronic widespread pain, based on findings from a previous report showing that RA is a predictor of fibromyalgia.
From the 889,938 adult patients identified, 4,016 developed fibromyalgia and 1,739 chronic widespread pain over the course of a 10-year follow-up period.
Results showed that all three disorders were associated with a significantly higher risk of fibromyalgia later in life (IRR of 3.64, 2.83, and 2.32 for patients with RA, endometriosis and IBD, respectively). However, only RA and endometriosis were linked to a significantly higher risk of chronic widespread pain (IRR of 2.96 and 5.02 for patients with RA and endometriosis, respectively).
In addition, statistical analyses revealed that fibromyalgia was associated with an increased risk of RA, while chronic widespread pain was linked to a higher risk of endometriosis.
“This study shows that RA, endometriosis and IBD are all risk factors for later fibromyalgia and chronic widespread pain, consistent with a hypothesis of central sensitization as an effect of a painful underlying condition,” the scientists concluded.