Role of Positron Emission Tomography in Assessing Disease Activity in Ulcerative Colitis: Comparison with Biomarkers.

Background: Disease activity in ulcerative colitis (UC) is best assessed clinically by Mayo score. 18-Fluorodeoxyglucose positron emission tomography-computerized tomography (FDG PET-CT) is a noninvasive imaging technique to assess extent, disease activity and response to treatment of UC, especially in high risk population or patients unwilling for endoscopy.

Aims: We conducted a prospective observational study with the aim of assessing and correlating UC disease activity by clinical criteria, endoscopy, histology, serum and fecal biomarkers, and FDG PET-CT.

Methods: Sixty eligible patients of UC were enrolled into three groups (26 remission, 24 moderate and 10 severe activity) as per Mayo score and FDG PET-CT was performed within 72 h of colonoscopy. ESR, CRP, and fecal calprotectin (FC) levels were determined for all patients.

Results: Of 60 enrolled patients, 10% patients had proctitis, 43.3% left-sided colitis, and 46.7% extensive colitis. ESR, CRP, FC levels, and rectal PET activity were significantly higher in groups with moderate and severe disease activity. Rectal PET activity showed a significant correlation with the Mayo score (k = 0.465, p < 0.001), endoscopic subscore (k = 0.526, p < 0.001), histological score (k = 0.496, p < 0.001), and FC (k = 0.279, p = 0.031). Extent evaluation by FDG PET-CT and colonoscopy showed a significant correlation (k = 0.582, p < 0.001). Besides, FDG PET-CT identified sacroiliitis in one patient and adenocarcinoma in one patient.

Conclusion: FDG PET-CT is a reliable noninvasive tool for detection of disease activity, extent in UC with good correlation with Mayo score, histology and fecal biomarkers and accurate predictor of disease remission.