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

Abstract 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.