Prevalence and Radiographic Progression of Hip Involvement in Patients With Ankylosing Spondylitis Treated With Tumor Necrosis Factor Inhibitors

OBJECTIVE: To examine the prevalence of hip involvement between sexes in patients with ankylosing spondylitis (AS) treated with tumor necrosis factor inhibitors (TNFi) and to estimate the effect of TNFi on radiographic progression of hip involvement compared to the spine. METHODS: Two hundred ninety-nine patients with AS treated with TNFi (215 men; median age: 43 yrs [IQR 36-52], median disease duration: 7.6 yrs [IQR 2-15]) were evaluated for hip involvement, defined radiographically as Bath AS Radiological Hip Index (BASRI-hip) score ≥ 2. Those who received TNFi for ≥ 2 years (263/299) were assessed for radiographic progression. Radiographs of the pelvis and spine, obtained at baseline (ie, before TNFi initiation), were compared retrospectively to those obtained after 2.5 (SD 0.7) years and 7.0 (SD 2.3) years of TNFi treatment. Both hips were scored by BASRI-hip score and mean joint space width (MJSW). Spinal radiographs were scored by modified Stoke AS Spinal Score (mSASSS). RESULTS: The prevalence of hip involvement at baseline was 113/299 (38%) patients, of whom 87/215 (41%) were male and 26/84 (31%) were female (P = 0.10). In both sexes with hip involvement at baseline, BASRI-hip score and MJSW did not change significantly during follow-up. In males and females without baseline hip involvement, the BASRI-hip score remained unchanged after 2.5 (SD 0.7) years but increased significantly after 7.0 (SD 2.3) years, without reaching the cut-off of 2. In contrast, the MJSW slightly decreased at the 2 follow-up timepoints (ie, after 2.5 and 7.0 yrs). The mSASSS increased significantly during the follow-up in both sexes, regardless of hip involvement. CONCLUSION: In our study, approximately one-third of patients with AS had hip involvement, which seemed to stabilize with TNFi treatment. No sex differences in the prevalence or progression of this manifestation were found.