The Prevalence and Clinical Associations of Subclinical Sacroiliitis in Inflammatory Bowel Disease.

Background: Sacroiliitis, an inflammatory arthropathy associated with ankylosing spondylitis (AS), is found in patients with inflammatory bowel disease (IBD) but may go undiagnosed. The aims of this study were to assess prevalence of sacroiliitis in IBD and to determine association between clinical characteristics of IBD and sacroiliitis.

Methods: Inflammatory bowel disease patients undergoing abdomino-pelvic computed tomography (CT) for any indication (2006-2015) were identified. Using standardized CT scoring, sacroiliitis was confirmed. Two blinded readers used a standardised model where presence of ankylosis or erosion score >3 indicated sacroiliitis. Inflammatory bowel disease scoring was blinded to the presence of sacroiliitis. Demographics, IBD characteristics, clinical activity (Harvey Bradshaw Index >4, Mayo >2, as denoted by attending physician), endoscopic activity (Simple Endoscopic Score for Crohn's Disease >4/Mayo subscore >1), and arthritis/extraintestinal manifestations (EIMS) were recorded. Comparisons were made between those with/without sacroiliitis.

Results: Three hundred sixteen patients were included (50% male; 74% Crohn's disease [CD]). Computed tomography scoring identified 49 (16%) with sacroiliitis. Radiologists had reported sacroiliitis in 33% of these. Five patients had been to a spondylitis clinic. Thirty-three of 49 had abdominal x-rays; 64% of these fulfilled the imaging component of Modified New York criteria for AS. More than 5 sacroiliac erosions were associated with radiologist-reported sacroiliitis (P < 0.0001). There was no difference in prevalence between CD and ulcerative colitis. Sacroiliitis was associated with male sex (63.3% vs 47.9%; odds ratio [OR], 1.8; P = 0.04), known arthritis (41% vs 12%; OR, 4.7; P < 0.0001), pain as an IBD symptom (77.7% vs 56.9%; P = 0.03), and CD inflammatory phenotype (P = 0.01). Endoscopic activity, location, and extent were not associated.

Conclusions: Sacroiliitis is underdiagnosed in IBD and is associated with male sex, arthritis, and inflammatory CD. Data support targeted screening in at-risk patients.