Structural Equation Modelling of Sleep Quality Determinants in Rheumatoid Arthritis: Pain, Inflammation and Psychological Factors

Background: Sleep disturbances are highly prevalent in rheumatoid arthritis (RA) patients, significantly impacting quality of life and disease outcomes. However, the complex relationships between sleep quality, pain, inflammation and psychological factors remain poorly quantified. Methods: This cross-sectional study included 325 RA patients from multiple rheumatology centres across Saudi Arabia and the Middle East. Sleep quality was assessed using the Pittsburgh Sleep Quality Index and Insomnia Severity Index. Pain was evaluated using multiple measures to distinguish between inflammatory pain (Visual Analogue Scale pain and Brief Pain Inventory) and non-inflammatory pain (pain DETECT and Pain Catastrophizing Scale). Inflammation was assessed through disease activity measures and inflammatory markers. Psychological factors were measured using validated scales for depression, anxiety and stress. Structural equation modelling was used to test direct and indirect relationships between these factors and sleep quality. Results: The final structural equation model explained 72% of the variance in sleep quality. Non-inflammatory pain ( β = 0.31, P < 0.001) and psychological factors ( β = 0.48, P < 0.001) had significant direct effects on sleep quality, whereas inflammation and inflammatory pain influenced sleep quality primarily through indirect pathways. The total effects were largest for psychological factors ( β = 0.48) and non-inflammatory pain ( β = 0.50), followed by inflammation ( β = 0.33) and inflammatory pain ( β = 0.23). Multi-group analyses revealed stronger effects of non-inflammatory pain on sleep quality in females and older patients, while psychological factors had stronger effects in younger patients. Conclusion: Sleep quality in RA is determined by a complex interplay of pain mechanisms, inflammation and psychological factors. Non-inflammatory pain and psychological factors have the strongest direct effects on sleep quality, while inflammation and inflammatory pain exert their influence primarily through indirect pathways. These findings suggest that addressing central pain mechanisms and psychological comorbidities may be particularly important for improving sleep in RA patients.