Fibromyalgia in systemic autoimmune rheumatic diseases: a mixed-methods study of patient and clinician perspectives.

Fibromyalgia is frequently diagnosed alongside systemic autoimmune rheumatic diseases (SARDs), yet impacts remain poorly understood. This study aimed to examine patients' and clinicians' perspectives of the psychosocial, clinical, and relational impact of fibromyalgia as a co-diagnosis in SARDs. We employed explanatory mixed-methods study integrating survey data from 1269 adults with SARDs, and interviews with patients (n = 19) and clinicians (n = 21). Outcomes included wellbeing (WEMWBS, 14-70), trust, confidence in receiving medical help, adaptation, satisfaction with care (all 1-5), and self-rated health (0-100). Independent t-tests compared outcomes by fibromyalgia status and by patients' diagnostic acceptance. Qualitative open-text responses and interviews were analysed thematically. Among participants (95.1% female n = 1207; lupus 31.0% n = 393 and rheumatoid arthritis 31.3% n = 397), fibromyalgia was reported by 25.9% (n = 329) of whom 52.8% (n = 174) questioned diagnostic accuracy. Compared with those without fibromyalgia, affected participants reported significantly lower wellbeing (mean difference(SD) = -4.206(0.608)), trust in GPs (mean difference(SD) = -0.239(0.092)) and rheumatologists (mean difference(SD) = -0.515(0.097)), confidence in receiving help (mean difference(SD) = -0.459(0.073)), and satisfaction with care (mean difference(SD) = -0.563(0.073)), alongside poorer adaptation (mean difference(SD) = -0.223(0.066)) and life satisfaction (mean difference(SD) = -0.519(0.071)), but higher self-rated health (mean difference(SD) = 11.107(1.411); all p < 0.05). Diagnostic acceptance showed minimal quantitative differences across outcomes. Thematic analysis highlighted that diagnostic uncertainty was driven by overlapping symptoms and limited biomarkers. Variations in clinician practices affected patients' trust and acceptance. Furthermore, misdiagnosis and dismissal led to stigma, delayed recognition of conditions, and considerable patient distress. In SARDs, fibromyalgia diagnosis is associated with poorer wellbeing and reduced trust in healthcare providers, irrespective of diagnostic acceptance, and often reflects diagnostic uncertainty. Mechanism-based explanations may help improve communication and provide greater clinical utility than categorical diagnostic labelling.