Evaluation of the agreement between the ACR 1990 fibromyalgia tender points and an enthesitis score in patients with axial spondyloarthritis.

Objectives: Coexistence of FM represents a challenge in the evaluation of enthesitis in patients with axial spondyloarthritis (axSpA) due to a possible overlap between the tender points (TP) due to enthesitis and those of FM. The objective was to assess the agreement between the MASES enthesitis score and the tender points of the ACR 1990 criteria in patients with axSpA.

Methods: This was a cross-sectional ancillary analysis of the Predict-SpA study (NCT03039088). Patients had a diagnosis of axSpA according to their rheumatologist and an indication to start a TNFα blocker. All patients were screened for FM according to the FiRST questionnaire. A physician was asked to assess 31 anatomically described sites in a random order without knowing to which instrument the site belonged (i.e. the 18 ACR 1990 TP and the 13 MASES sites). Agreement between the MASES and the ACR 1990 TPs by the intraclass correlation coefficient (ICC), also stratified by the presence/absence of concomitant FM according to the FiRST.

Results: Among the 526 patients, 53% were men and 202 (38%) had FM. Radiographic sacroiliitis and MRI sacroiliitis were present in 56% and 68% patients, respectively. Patients were mostly men (53.4%) with radiographic and MRI sacroiliitis in 56% and 68% patients, respectively. Mean number of ACR 1990 TP was 5.4 (s.d. 4.6) and mean MASES was 4.2 (s.d. 3.6). ICC between both scores was 0.7 [95% CI (0.6, 0.8)]. ICC between both scores was 0.6 [95% CI (0.3, 0.8)] and 0.7 [95% CI (0.6, 0.7)] for patients with and without FM, respectively.

Conclusion: These results suggest a significant overlap between both scores in patients with axSpA, including in those without concomitant FM.

Trial Registration: clinicaltrials.gov, https://clinicaltrials.gov, NCT03039088.