Indolent T cell lymphoproliferative disorder with villous atrophy in small intestine diagnosed by single-balloon enteroscopy.

Chronic diarrhea is one of the major symptoms in gastroenterology. However, this may be caused by pathologic conditions for which the diagnosis is critical. Villous atrophy, as an endoscopic lesion, accompanied by chronic diarrhea can occasionally be observed in the patients with inflammatory diseases of the gastrointestinal (GI) tract. Herein, we present a case with persistent diarrhea accompanied by intestinal wall thickening without any other significant endoscopic features other than villous atrophy in the jejunum and the ileum, where we diagnosed as an indolent T cell lymphoproliferative disorder (T-LPD) of the GI tract, defined in the 2016-2017 revised World Health Organization classification, via single-balloon enteroscopy (SBE). Interestingly, we found the same lymphocyte infiltration from the distal third portion of the duodenum, where gastroscopy could not reach, via SBE, even though no endoscopic findings were observed such as villous atrophy. Since infiltrating cells in the intestinal tissues were CCR4+, mogamulizumab was administered with resulting durable symptomatic remission for more than 2 years. Patients with persistent diarrhea may have serious small intestinal disorder including not only chronic inflammatory diseases but also lymphoid neoplasmic conditions including T-LPD of GI tract.