Performance of standardized patient reported outcomes developed for spondyloarthritis in primary and concomitant forms of fibromyalgia.

Background: In spondyloarthritides (SpA) and fibromyalgia (FM), patients suffer from generalized pain. The impact of FM on PRO validated in SpA has not been systematically studied.

Objective: Study the performance of PROs developed for SpA in patients with primary (p) FM without chronic inflammatory-rheumatic disease vs. SpA without and with concomitant (c) FM.

Methods: Patients with pFM, axSpA or PsA and indication for treatment adaptation were prospectively included. Standardized PROs were assessed: BASDAI, ASDAS-CRP, DAPSA, patient´s global assessment, BASFI, LEI, MASES, SPARCC Enthesitis Score and FIQ.

Results: 300 patients were included (100/diagnosis). More males were found in axSpA vs. PsA and pFM group (67, 33 and 2/100, respectively), while 12 axSpA (axSpA+) and 16 PsA (PsA+) patients had cFM. pFM patients showed significantly higher scores in all assessments vs. axSpA or PsA, with exception of ASDAS-CRP (3.3 ± 0.6 in FM vs. 3.1 ± 1.0 in axSpA) and duration of low lumbar morning stiffness. Similar results were also found in the subanalysis of female patients only. In addition, patients with axSpA + or PsA + showed no differences to patients with pFM, while significantly higher scores were found for FM, axSpA + and PsA + for almost all FIQ items compared to axSpA- or PsA-.

Conclusions: PROs originally developed for axSpA or PsA need to be interpreted differently in the presence or absence of cFM. ASDAS-CRP and duration of lumbar morning stiffness were not affected by cFM. FM-specific questionnaires also showed high scores in patients with SpA with cFM but not in those without.