Articular involvement in antiphospholipid syndrome: Clinical, laboratory, and imaging characterization

Introduction Antiphospholipid syndrome (APS) is characterized by antiphospholipid antibodies (aPL) and thrombotic and/or obstetric events. Musculoskeletal manifestations, particularly arthralgia, are frequently reported, although their clinical and pathophysiological correlates remain incompletely characterized. Objective To characterize the clinical, laboratory, and imaging features of articular involvement in primary and systemic lupus erythematosus (SLE)-associated APS compared with healthy controls. Methods This cross-sectional study included 99 participants aged 18–50 years: 38 with primary APS (PAPS), 26 with APS associated with SLE (APS/SLE), and 35 age- and sex-matched healthy controls. APS patients fulfilled the Sydney classification criteria, and those with SLE were classified according to the 1997 American College of Rheumatology criteria. Arthralgia was clinically assessed. Radiographic and high-resolution ultrasound (US) evaluation of the hands and wrists was performed. Laboratory tests included erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF), and anti-cyclic citrullinated peptide (anti-CCP) antibodies. Results Age was comparable across groups ( p = 0.206). In the comparative analysis of aPL profiles between PAPS and APS/SLE, lupus anticoagulant was the most prevalent antibody in both groups (94.7% vs 96.2%; p = 0.792). IgG anticardiolipin and anti-β 2 -glycoprotein I antibodies were more frequent in PAPS (42.1% vs 15.4%, p = 0.024; 32.4% vs 0%, p = 0.019). Arthralgia was more frequent in APS/SLE than in PAPS (80.8% vs 50%; p = 0.013), as was morning stiffness (46.2% vs 21.1%; p = 0.033). ESR levels were higher in APS/SLE compared with PAPS and controls (median 19.5 vs 14 vs 6 mm/h; p < 0.001). CRP levels did not differ significantly among groups ( p = 0.118). RF positivity was low (2.6% in PAPS) and did not differ among groups (p = 1.000), and anti-CCP IgG antibodies were absent in all groups. Radiographic findings were mild and comparable. On US, joint effusion was more frequent in APS/SLE than in PAPS and controls (26.9% vs 2.6% vs 2.9%, respectively; p = 0.001), whereas synovitis, tenosynovitis, Power Doppler signal, and other findings showed no significant differences. Conclusion Articular manifestations are common in APS, particularly in APS/SLE, but are not consistently supported by objective evidence of inflammation. This dissociation suggests that musculoskeletal involvement may not be primarily mediated by overt inflammatory mechanisms.