Up to 40% of people with IBD  — a group of disorders that cause chronic inflammation in the gastrointestinal tract — develop disorders beyond those of the GI tract, including spondyloarthritis, a type of arthritis that affects the spine and, in some people, the joints of the arms and legs.

Fibromyalgia can also occur in association with IBD, and worsen chronic pain in these patients. However, its true prevalence and origin — whether it develops as a complication of IBD, or occurs independently in susceptible individuals — are still controversial.

Some people with IBD also have polyenthesitis — inflammation of several entheses, the connective tissue between tendons or ligaments and bones — as a result of concomitant spondyloarthritis.

“A major challenge in this area is that polyenthesitis that may be associated with SpA [spondyloarthritis] in IBD is clinically very difficult to differentiate from FM [fibromyalgia], leading to potential misclassification and either under-treatment or overtreatment of patients,” the researchers wrote.

To address this issue and estimate the prevalence of pure fibromyalgia and fibromyalgia associated with spondyloarthritis, investigators analyzed clinical data from a group of 301 patients with IBD — 150 with Crohn’s disease and 151 with ulcerative colitis  — enrolled at two Italian centers.

Researchers also investigated if ultrasound imaging (echography) could be used as a diagnostic tool to distinguish spondyloarthritis from fibromyalgia associated with IBD. Two types of ultrasound exams were performed: conventional ultrasound and power Doppler, a technique that is more sensitive and provides detailed information about blood flow.

Among the 301 IBD patients examined, 37 (12.3%) met the diagnostic criteria for fibromyalgia established by the American College of Rheumatology (ACR 2010). Of these, 9% had pure fibromyalgia, and 3.3% had both fibromyalgia and spondyloarthritis.

Fibromyalgia was more prevalent in women (81%), those age 45 or older, and among those who had a slightly longer history of IBD. However, fibromyalgia was not related to smoking, having a sedentary job, body mass index, or psoriasis, an autoimmune disorder that affects the skin.

Patients with IBD and fibromyalgia also had a higher number of inflamed entheses, as well as more active disease and functional limitations, based on clinical examinations (Leeds Enthesitis Index) and patient reports (BASDAI and BASFI scores).

After comparing ultrasound examinations of IBD patients with spondyloarthritis and fibromyalgia, researchers found that acute and chronic alterations in enthesis were more common among those with IBD and spondyloarthritis (1.7 acute changes per patient), than among those with IBD and fibromyalgia (0.7 acute changes per patient).

A positive Doppler signal at ligaments and joints indicative of an abnormal amount of blood vessels (vascularization) was also more frequent among patients with IBD and spondyloarthritis, than among those with IBD and fibromyalgia.

Altogether, these findings suggest that fibromyalgia occurs in a significant proportion of IBD patients, increasing symptom burden and worsening their quality of life. In some cases, fibromyalgia and spondyloarthritis may coexist, “complicating clinical decision making.”

“Subjective measures and patient-reported outcomes may overestimate disease activity, and thus are unreliable in therapeutic decision making in clinical practice, since they may lead to intensification of, or switching, immunotherapy when it is not necessarily warranted,” the researchers wrote.

“Clinical data complemented by more objective measures of inflammation such as entheseal sonography can help clarify the diagnosis,” they added.