Impact of fibromyalgia on patient acceptable symptom state in Thai patients with spondyloarthritis: A cross-sectional study

Abstract

Background: The interplay between inflammatory disease activity and centralized pain processing represents a significant challenge in the clinical management of spondyloarthritis. In patients with spondyloarthritis, the co-occurrence of fibromyalgia may significantly influence patients' perception of their symptom burden and treatment satisfaction. This study aimed to determine the prevalence and impact of fibromyalgia and examine the association of fibromyalgia severity score (FS) and clinical parameters with Patient Acceptable Symptom State (PASS) in Thai patients with spondyloarthritis. Methods: A cross-sectional study consecutively enrolled Thai patients with spondyloarthritis. Fibromyalgia was diagnosed using the 2016 revision of the 2010/2011 American College of Rheumatology criteria. Collected data included demographics, physical examination, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Pittsburgh Sleep Quality Index (PSQI), EuroQoL 5-dimensions (EQ-5D) Index, and PASS. Regression analysis identified factors associated with PASS. Results: Among 218 participants, 12 (5.5%) had fibromyalgia. These patients had significantly higher median BASDAI (5.1 vs. 1.5, p = 0.001), BASFI (3.8 vs. 0.8, p = 0.004), and PSQI (8.0 vs. 5.0, p = 0.046), a lower mean EQ-5D index (0.63 vs. 0.88, p = 0.001), and fewer PASS-yes responses (8.3% vs. 72.3%, p < 0.0001). The PASS-yes group had lower median FS than the PASS-no group (2.0 vs. 6.5, p = 0.001). In multiple regression models, BASDAI < 4 (odds ratio [OR] range 4.05–4.62), FS < 3 (OR range 3.27–3.83), and PSQI ≤ 5 (OR range 2.01–2.40) were independently associated with PASS, whereas BASFI was not. Conclusions: Fibromyalgia prevalence is elevated in patients with spondyloarthritis, and significantly impairs health-related quality of life and symptom perception. Low disease activity, good sleep quality, and FS < 3 are independently associated with achieving an acceptable symptom state. These findings highlight the importance of assessing fibromyalgia to better understand patient-reported outcomes and guide clinical decision-making.