Proposed diagnostic algorithm in EATL. The recurrence of celiac symptoms in a patient with CD under GFD, or the persistence of celiac symptoms in a recently diagnosed CD patient despite a GFD followed for more than 12 months, should raise the suspicion of RCD. In that case, the compliance to GFD should be ascertained, and, if sufficient, patients should undergo upper endoscopy with collection of duodenal biopsies. A rate of more than 20% of aberrant IELs, assessed by flow cytometric analysis of freshly isolated cells, points toward a diagnosis of RCD2. In that case, EATL should be excluded through both imaging (either MR enteroclysis or CT scan together with PET scan) and double-balloon endoscopy with collection of small bowel biopsies. The occurrence of celiac and B symptoms (fever of no evident cause, night sweats, and weight loss of > 10% of body weight) in a patient without a known history of CD and on gluten-containing diet (primary EATL) or the co-occurrence of B symptoms and cachexia in the 2 aforementioned patient subsets suspected to be refractory (secondary EATL) should raise the suspicion of EATL. In that case, patients should undergo both upper endoscopy and double-balloon enteroscopy with collection of small bowel biopsies and imaging procedures (either MR enteroclysis or CT scan together with PET scan). In the case of EATL confirmation, a staging should be performed through bone marrow examination, CT scan of the thorax, and sonography of the neck.