Background/Purpose: Axial SpA has been reported in 4-16% of patients with Crohn’s disease (CD). However, some plain radiograph or magnetic resonance imaging (MRI) studies in Crohn’s population suggest presence of sacroiliitis in up to 40% patients. Whether axial SpA is underdiagnosed and hence undertreated is unclear, especially since it does not correlate with CD activity. This study utilizes standardized MRI SI joint (SIJ) imaging to determine prevalence of axial SpA in a cohort of CD patients and investigate its relationship with other clinical and serologic measures. In addition, we compare MRIs from our cohort of CD patients with separate cohorts of patients with known axial SpA with and without inflammatory bowel disease (IBD).

Methods: Adult consecutive patients meeting pathological, radiological and/or endoscopic criteria of CD and not currently on any biologic except vedolizumab, were prospectively enrolled from an IBD Clinic. Data collected included length of CD, history of joint/back pain, HLA-B27 status, BASMI, BASDAI, Harvey-Bradshaw Index (HBI) scores- a measure of CD activity, Ankylosing Spondylitis Disease Activity Score-C reactive protein (ASDAS-CRP). All patients underwent T1 and short tau inversion recovery (STIR) sequence MRI of SIJ. 3 expert readers, blinded to clinical history reviewed MRIs for presence of active and/or structural lesions globally indicative of SpA, for ASAS MRI positivity, detailed lesion scores using the SpA Research Consortium of Canada (SPARCC) SIJ inflammatory and structural scoring methods after calibration using validated modules. These images were compared to MRIs from age and sex-matched AS patients with and without IBD.

Results: 32 CD patients were enrolled: 76% females, 80% white, median age 36.4 years (IQR 27.2 – 49) with moderate CD activity (mean HBI 8.8 ± SD 4.5). 56% had peripheral SpA and only 1 was HLA-B27 positive. 20 reported back pain and 14 (70%) met ASAS inflammatory back pain (IBP) criteria. Mean BASDAI, ASDAS-CRP and BASMI were higher than patients without back pain (p <0.05). Total of 9 SIJ MRIs (35% of all patients with back pain and 16% of those without) showed global evidence of SpA (bone marrow edema BME ≥ 2 and/or structural lesions) and 6 out of those were ASAS positive (presence of active inflammation/BME), including 2 asymptomatic patients. Older age (OR 1.4, 95% CI 1.04 – 1.90) and higher BASMI (OR 3.2 95% CI 1.1-9.6) were associated with MRI SpA findings. But presence of IBP, peripheral SpA, CD duration, BASDAI, ASDAS-CRP or HBI did not show association. Compared to historic cohort of AS patients with (n=23) and without (n=24) IBD, CD patients with IBP had similar BASDAI and ASDAS-CRP scores (p <0.05) but they had lower BME and structural lesions (p 0.02 and <0.001) compared to IBD with and without SpA.

Conclusion: MRI evidence of axial SpA was 35% and 16% in our cohort of CD patients with and without back pain respectively. MRI is a valuable tool to diagnose axial SpA in CD patients with back pain, especially those who are older and has evidence of restricted spinal mobility on exam. Presence of IBP did not show association, as previously suggested, although these patients experience similar morbidity as our comparator cohort with known AS with or without IBD.