Lower adalimumab trough levels are associated with higher bowel wall thickness in Crohn's disease

Background: In Crohn's disease, higher adalimumab trough levels and negative anti-adalimumab-antibodies associate with better clinical and endoscopic outcomes. Intestinal ultrasound has become a relevant non-invasive method to monitor treatment. However, data on the association between adalimumab levels and bowel wall thickness measured with ultrasound is limited. Objective: The purpose of this study was to examine the possible association between the sonographic transmural-thickness and adalimumab trough levels. Methods: This prospective observational cohort study was conducted at Sheba Medical Center in 2014–2018. Crohn's disease patients on adalimumab maintenance therapy with intestinal ultrasound performed within <30 days of trough level measurement were included. Associations between terminal ileum and colonic thickness, adalimumab levels and therapy retention were assessed. Results: Fifty events of ultrasound with concomitant adalimumab trough level measurements in 44 Crohn's disease patients were included. Patients with trough level <3 μg/ml had significantly higher bowel wall thickness, both for terminal ileum (p = 0.04) and colon (p = 0.02). Thirty-two patients continued adalimumab therapy over one year. The adalimumab retention rate was higher among those with terminal ileum thickness <4 mm (p = 0.03). Conclusion: Lower adalimumab trough levels were associated with higher bowel wall thickness indicating poorer therapy outcome. Transmural thickness measurement with ultrasound may be a useful target for guiding biologic therapy in Crohn's disease.