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Letter to the editor: anti-TNF therapy and radiation exposure in Crohn's disease: chicken or egg?

We read with interest the excellent article by Magro et al ‘Assessing cumulative radiation and predictive factors for higher radiation exposure in Crohn’s disease (CD) patients’.[1] They identified penetrating phenotype, abdominal surgery, and non-colonic disease as predictors for high-radiation exposure. Despite increased awareness of the potential cumulative downstream effects of ionising radiation, few studies, including ours, have quantified radiation exposure in patients with inflammatory bowel disease (IBD) noting penetrating disease, corticosteroid resistance or dependency, and previous surgery as also influencing cumulative radiation dose.[1–4] Additionally, Magro et al. found that anti-TNF therapy was followed by a sustained increase in cumulative radiation.[1] Data on modern therapeutic paradigms influencing radiation exposure in IBD are limited, with only two other studies reporting the effect of anti-TNF therapy on radiation exposure in CD.[5,6] After one year of initiating Anti-TNF therapy as compared to using corticosteroids, Patil et al. noted a significant reduction in the number of radiological examinations (5.5 vs. 3.7, p50.01) and cumulative radiation dose (28.1 vs. 15.0 mSv, p50.01), and this effect was largely attributed to decreased use of computerised tomography (CT) scans.[5] We recently reported our experience in a large series of CD patients treated with anti-TNF or corticosteroids and noted a significant decrease in the number of radiological studies (2.0 vs. 0.2, p1⁄4 0.001) and cumulative radiation dose (3.1 vs. 0.3 mSv, p1⁄4 0.01) in the anti-TNF compared to the corticosteroid group.[6] Even 3 years following therapy, we noted significant increase in radiological studies (2.3 vs. 0.3, p1⁄4 0.003) and cumulative radiation dose (6.8 vs. 1.3 mSv, p1⁄4 0.003) in the corticosteroid group compared to the anti-TNF group. In this respect, the observation by Magro et al. that Anti-TNF therapy is associated with increase in radiation exposure raises as many questions as it seems to answer.[1] Evolving definitions of disease control, placing emphasis on mucosal healing rather than symptoms alone have changed therapeutic paradigms, with often earlier introduction of combined immunomodulatory therapy in well-selected patients, altering clinician perception of what can be achieved through abrogation of intestinal inflammation and its impact on disability.[7,8] It seems plausible that anti-TNF therapy through its ability to induce clinical remission and to its extent mucosal healing, could reduce exposure to ionising radiation, which itself is often a function of disease activity driving investigation. Yet, differences in patient phenotype, inflammatory burden and timing of effective immunomodulatory therapy will influence the threshold and need for cross-sectional imaging for reliable assessment of mucosal healing or indeed disease-related complications as noted by Magro et al. To complicate matters, concerns with regard to opportunistic infection and risk of malignancy over longer periods of immunosuppressant therapy, could instigate further investigation, increasing exposure to ionising radiation, and arguably mitigate any radiation sparing effect of anti-TNF therapy. As definitions of disease remission evolve, reliance on intestinal imaging is set to increase. The choice of investigation should be driven by the clinical question, available expertise, and economic factors.[9] Although CT imaging remains a valuable modality with a high sensitivity and specificity for the detection of luminal and extra luminal disease and its complications, the real risk of cumulative radiation might be reduced by the use of low-dose CT technology or non-ionising radiation, such as magnetic radiation (MR), whenever possible with comparable diagnostic effectiveness.[10] Cohort studies of sufficient duration will be necessary to link meaningfully any effect of immunosuppressive therapy with ionising radiation. Magro et al. are to be congratulated for this study, which emphasises collaboration between clinicians and radiologists in planning imaging, yielding the best possible information with the least potential for harm.