Relationship between sacroiliac joint involvement and intestinal disease activity in newly diagnosed Crohn’s disease

BACKGROUND: Axial musculoskeletal involvement represents an important component among the extraintestinal manifestations of Crohn's disease (CD). Sacroiliac joint (SIJ) involvement can be detected at an early stage using imaging modalities. The aim of this study was to evaluate the relationship between SIJ involvement and laboratory parameters, intestinal disease activity, and SIJ anatomical variations in patients with newly diagnosed CD. METHODS: In this single-center retrospective imaging-pathology correlation study, 68 adult patients with a multidisciplinary diagnosis of Crohn's disease established through clinical, endoscopic, radiological, and histopathological evaluation who underwent magnetic resonance enterography (MRE) and pelvic computed tomography (CT) examinations at the time of diagnosis were included. SIJ findings were classified as MRE-detected bone marrow edema-like findings, CT-detected structural SIJ abnormalities, or no involvement. SIJ anatomical forms were evaluated according to the morphological variation classification described by Ziegeler et al. Intestinal disease activity was analyzed using endoscopic (Mayo-based categories), histopathological (Geboes grading system), and clinical phenotype classification (Montreal classification) parameters. RESULTS: MRE-detected bone marrow edema-like SIJ findings were detected in 9 patients (13.2%), CT-detected structural SIJ abnormalities in 9 patients (13.2%), and no SIJ involvement in 50 patients (73.5%). Platelet count, ferritin levels, and total iron-binding capacity (TIBC) differed significantly among the groups (p < 0.05). A statistically significant association was observed between endoscopic disease activity categories and SIJ findings (Fisher's exact p < 0.001); however, the distribution pattern did not demonstrate a consistent increase in SIJ abnormalities with increasing endoscopic activity. In histopathological evaluation, a statistically significant association was found between SIJ involvement patterns and histopathological activity (Fisher's exact p < 0.001); however, this association was primarily driven by the complete absence of severe histological activity in the CT-detected structural SIJ abnormalities group. In contrast, no significant relationship was found between disease location or behavior according to the Montreal classification and SIJ involvement patterns (p > 0.05). Similarly, no significant association was identified between SIJ anatomical variations and involvement patterns (p = 0.845). CONCLUSION: In patients with newly diagnosed CD, SIJ involvement appears to be most closely associated with histopathological disease activity. The association with endoscopic categories was statistically significant but showed an inverse, non-monotonic pattern, with SIJ findings clustering predominantly among patients with lower Mayo scores. In contrast, SIJ anatomical variations do not appear to play a determining role in the development of inflammatory or structural changes. These findings are exploratory in nature and indicate that prospective studies with clinical and rheumatologic correlation are required to better elucidate the relationship between intestinal and axial involvement in CD.