Coexistence of fibromyalgia (FM) in patients with spondyloarthritis (SpA) impacts patient-reported outcomes for disease activity and treatment responses, according to the study, “Evaluation of the impact of fibromyalgia in disease activity and treatment effect in spondyloarthritis,” published in the Arthritis Research & Therapy journal.
FM often co-exists with SpA, a term that includes a spectrum of chronic inflammatory diseases involving both the joints and the entheses (the sites where the ligaments and tendons attach to the bones). As a result, this FM-SpA association presents diagnostic and treatment dilemmas, since some SpA symptoms (e.g., pain at entheses, fatigue, stiffness, and tenderness) can also be found in FM patients.
The team of researchers estimated the prevalence of FM in a population of patients with SpA and compared the demographics/disease features, and the effects of TNF inhibitor (TNFi) treatment in patients with and without FM. To this end, the team recruited patients (18 and older) with a diagnosis of SpA according to a rheumatologist; FM diagnosis was defined by a score equal or superior to 5/6 in the Fibromyalgia Rapid Screening Tool (FiRST).
In total, 196 SpA patients participated in the study with 42 patients (21.4 percent) positive for FM. Researchers found no statistical significant differences in the prevalence of FM when comparing the fulfillment of the Assessment of the Spondyloarthritis International Society (ASAS) criteria for peripheral/axial SpA. No differences were found for imaging versus the clinical arm of the ASAS criteria.
Importantly, patients with coexisting FM exhibited worsening symptoms, including a significantly higher burden with enthesitis, higher disease activity (BASDAI, or Bath Ankylosing Spondylitis Disease Activity Index, and global visual analog scale, or VAS) and poorer function scores (according to the Bath Ankylosing Spondylitis Functional Index, or BASFI, test). While no differences were observed with regard to the initiation of TNFi treatment, patients with FM presented a shorter retention rate of the first TNFi after two years.
These findings support the current ASAS classification criteria, and the clinical arm in particular. Moreover, they suggest that ongoing FM in SpA impacts the tools used to assess disease activity and severity, and might influence how clinicians evaluate treatment response, such as the retention rate of TNFi treatment.