ASSOCIATIONS BETWEEN ULTRASOUND CHRONIC LESIONS IN PERIPHERAL ENTHESES AND RADIOGRAPHIC STRUCTURAL SPINAL CHANGES IN MEN AND WOMEN WITH ANKYLOSING SPONDYLITIS

BackgroundAnkylosing spondylitis (AS) is characterised by spinal bone formation and enthesitis. Whether patients with spinal bone formation have a generalised bone formation phenotype also involving the peripheral entheses is not fully known.ObjectivesTo assess in cross-sectional analyses the association between chronic ultrasound (US) lesions in peripheral entheses with spinal bone formation and factors associated with spinal bone formation, overall and by sex.MethodsThe entheses at 14 sites at the extremities were examined in 173 patients (54 % men, mean age (SD) 55 (13) years and symptom duration 29 (13) years) with AS (modified NY criteria) using US. Entheses were assessed for structural components (enthesophytes, calcifications and erosions) according to the OMERACT definition [1]. Each lesion was evaluated 0 or 1 and summarised to a damage score (0-42). Spinal radiographs from the same time point were graded according to the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) and presence of syndesmophytes were determined. The associations between US damage score and mSASSS and factors associated with spinal bone formation were analysed with Spearman´s correlation analysis overall and by sex. Also, Mann Whitney´s test and multivariable logistic regression analysis with presence of ≥ 1 syndesmophyte as dependent variable and age, sex, BMI, smoking status, CRP, and US damage score as independent variables were used.ResultsPresence of any US structural component was found in 158 (91 %) of the patients with no significant difference between men and women (95 % vs 87 % respectively, p = 0.15). The US damage score was median (IQR) 4 (2 to 6) in the total group with a higher score in men compared to women, 4.5 (2 to 7) vs 3 (2 to 5), p = 0.002. In analogy, more men had presence of syndesmophytes in the spine compared to women, 63 % vs 35 %, p <0.001 and men had higher mSASSS compared to women; median (IQR) mSASSS in men 14 (3 to 43) compared to 2 (0 to 11.5), p<0.001. Men had higher body mass index (BMI), but there were no sex differences for age, symptom duration, CRP, and smoking status.The results from correlation analyses for US damage score and mSASSS, age, symptom duration, CRP, smoking status, and BMI are presented in the Table 1. Spinal bone formation (mSASSS) was positively correlated with the US damage score in the total group and in men. In both men and women, higher age was associated with higher US damage score. A comparison between patients with and without syndesmophytes showed that patients with syndesmophytes had higher US damage score than patients without syndesmophytes, median (IQR) 5 (3 to 7) and 3 (1 to 5) respectively, p<0.001. In the multivariable logistic regression analyses the US damage score was not independently associated with presence of syndesmophyte in the total group or in men. If age was excluded from the analyses though, the US damage score was significantly associated with presence of syndesmophyte, odds ratio (95 % CI) for total group 1.20 (1.05 to 1.37) and for men 1.26 (1.05 to 1.51).Table 1.Ultrasound damage scoreTotal group (n=173)Men (n = 94)Women (n = 79)rsp-valuersp-valuersp-valueAge, years0.44<0.0010.43<0.0010.51<0.001Symptom duration, years0.28<0.0010.34<0.0010.270.015BMI, kg/m20.210.0060.110.280.190.10Current or past smoking0.0390.610.180.090-0.100.37CRP, mg/L0.120.130.0280.790.200.073mSASSS, score0.31<0.0010.270.0100.200.084rs: Spearman´s correlations coefficientConclusionStructural lesions were common in the entheses in patients with long-standing AS. Men had more severe bone formation in the spine and the peripheral entheses compared to women. Chronic lesions at the entheses accumulate with increasing age and US damage score could not independently identify patients with syndesmophytes in this cohort with long-standing AS. However, if age was not considered, there was an association between bone formation in the peripheral entheses and the spine in men with AS.References[1]Balint, P et al. Ann Rheum Dis 2018;77:1730-1735Disclosure of InterestsAnna Deminger: None declared, Mats Geijer Speakers bureau: UCB Pharma, Novartis, Abbvie, Nicklas Nilsson: None declared, Martin Hedberg: None declared, Lennart T.H. Jacobsson: None declared, Helena Forsblad-d’Elia: None declared