Introduction
Ulcerative colitis (UC) is a chronic inflammatory bowel disease where accurate assessment of disease activity is essential for effective patient management. Endoscopy is the gold standard for evaluating mucosal inflammation, but non-invasive alternatives, such as transabdominal ultrasound (TAUS), are garnering interest.
Aims & Methods
This study aimed to evaluate the sensitivity of rectal wall thickness measurements using TAUS in assessing disease activity in ulcerative colitis, and to identify an ideal cut-off threshold by comparing results with endoscopic and histological findings.
In a prospective, observational study, we enrolled consecutive patients with UC who were referred to our tertiary center from May 2024 to April 2025. Eligibility required a scheduled TAUS within 30 days of a staging colonoscopy, without intervening therapy adjustments. Exclusion criteria included technically inadequate TAUS readings (e.g., due to anatomical variations or excessive gas interposition) and minor-aged patients. Each patient underwent TAUS performed by a single, experienced operator. A second experienced operator blind assessments were recorded to evaluate inter-observer variability. Rectal wall thickness was measured and compared with clinical, laboratory (CRP, fecal calprotectin), and endoscopic (MAYO score) indicators of disease activity. Histological status (active/inactive) and additional clinical data, including disease duration, extent, and therapy, were recorded.
Results
A total of 74 patients were analyzed, of whom 51.4% were female, with a median age of 55 years (IQR: 42–68). The majority presented with left-sided colitis (Montreal E2, 62.2%), followed by extensive colitis (E3, 25.7%) and proctitis (E1, 12.1%). The median disease duration was 12 years (IQR 5–23). Patients with an endoscopic MAYO score of 0 or 1 had a median rectal wall thickness of 4.95 mm (IQR 4.5–5.88), while those with a score of 2 or 3 had a median of 6.15 mm (IQR 5.3–6.7; p=0.003). Receiver Operating Characteristic (ROC) analysis for TAUS rectal wall thickness showed good discriminatory ability for endoscopic activity (cut-off: 5.55 mm, AUC 0.725, 95CI 0.597-0.853, Se 0.80, Sp 0.71), comparable to fecal calprotectin (cut-off: 277 µg/g, AUC 0.717, 95CI 0.589-0.845, Se 0.70, Sp 0.66; p=0.256) and superior to CRP (cut-off: 1 mg/L, AUC 0.511, 95CI 0.357-0.664, Se 0.50, Sp 0.50; p<0.0001). For histological activity, TAUS again performed well (cut-off: 5.55 mm, AUC 0.794, 95CI 0.682-0.906, Se 0.76, Sp 0.80), closely matching fecal calprotectin (cut-off 302, AUC 0.744, 95CI 0.627-0.861, Se 0.69, Sp 0.73; p=0.425) and outperforming CRP (cut-off 1.5, AUC: 0.631, 95CI 0.497-0.765, Se 0.62, Sp 0.63; p<0.0001). Inter-observer agreement for TAUS rectal wall thickness was excellent, with an intraclass correlation coefficient of 0.923 (p<0.0001), underscoring the reproducibility of this non-invasive method.
Conclusion
TAUS measurement of rectal wall thickness demonstrates promising sensitivity and reproducibility in detecting mucosal and histological activity in UC, aligning closely with established markers such as fecal calprotectin. A cut-off value of 5.55 mm showed good discriminatory performance in this cohort, suggesting potential utility as a non-invasive marker of disease activity..Given its non-invasive nature, low cost, and strong inter-observer agreement, TAUS is a valuable adjunct for routine UC monitoring. Combined with clinical and biochemical data, it may reduce the need for repeated endoscopy, minimizing patient burden, healthcare costs, and environmental impact.
