We thank Lambie and Tolan for their comment on our article.[1, 2] As underscored by the authors, how to assess Crohn's disease (CD) activity or remission is a key point in the era of biologics. To answer this question, the emergence of new therapeutic goals, such as mucosal healing or preventing digestive damage, have to be considered.
Although the CD Activity Index (CDAI) was the gold standard to define clinical response or remission, achieving these new goals warrant other tools for monitoring the therapeutic efficacy. In this context, biomarkers and magnetic resonance imaging (MRI) appear as very promising non-invasive tools. Contrary to Horsthuis’ meta-analysis, the creators of the magnetic resonance index of Activity (MaRIA) reported a very high-diagnostic accuracy in differentiating active from inactive segment (>0.8). This difference could be partly explained by the heterogeneity in defining disease activity or remission.
Although the performances of conventional or diffusion weighted MRI are probably lower for the detection of mild lesions, we considered that it is not prejudicial in monitoring therapeutic response. Is a patient with persistent mild disease after treatment without ulceration eligible for therapeutic optimisation? This is a key point in the real-life setting. Though deep ulcers are correlated with a more aggressive clinical course with an increased rate of penetrating complications and surgery, the natural history of mild lesions remains unknown.
As we focused on terminal ileal involvement, the choice of the most active segment as endpoint seemed to us appropriate. Though the apparent diffusion coefficient (ADC) measurement could be improved by using normalised measurements, polyethylene glycol in small volume is, in our experience, well-tolerated and DWI-MRI seems an objective, reproducible, non time-consuming and accurate tool in the assessment of CD activity.