The diagnosis of<unk>  T<unk><unk><unk>  of the GI tract depends on identifying the presentation, clinical course, and laboratory and histological findings given in the previous four sections. (Future studies may find that the diagnosis is supported by demonstrating the presence of the STAT3-JAK2 fusion gene in the CD4+ T<unk> s of suspicious tissues.) Laboratory studies Inspection of the entire GI tract by endoscopy and colonscopy generally finds mucosal redness, erosions, small superficial ulcerations, occasional small polyps, fissures, diverticula, and, rarely, tumor-like masses and deep ulcers. These lesions may be localized, occur in multiple sites, or extend throughout the GI tract; they are more common in the small intestine and colon but can also occur in the stomach, esophagus, oral cavity (e.g. palate), and rectum. Whole body computed tomography scans (i.e. CT scans) frequently find enlarged mesenteric lymph nodes (i.e. lymph nodes attached to the intestinal mesentery) and may show evidence of liver, spleen, and/or other organ involvement in cases which are advancing or have advanced to a malignant lymphoma. Positron emission tomography scans (i.e. PET scans) and positron emission tomography–computed tomography scans (i.e. PET-CT scans) likewise often show that the mesenteric lymph nodes in ITCLD-GT exhibit modestly increased metabolic or biochemical activity and, in cases of progressing or overt malignant disease, show increased activity in other organs. Inspection of patients' peripheral blood smearss and bone marrow tissues may identify excessive numbers of ITCLD-GT's T<unk> s and thereby likewise indicate progressing or malignant disease. Differential diagnosis Because of the radical differences in their prognoses and treatments, ITCLD-GT should be distinguished from the malignant, inflammatory, autoimmune, and other diseases that it can mimic. Key findings that distinguish ITCLD-GT from the following major diseases which ITCLD-GT may mimic are: * Extranodal NK/T-cell lymphoma, nasal type (ENKTCL-NT: Unlike ITCLD-GT, ENKTCL-NT a) is an Epstein-Barr virus-associated<unk>  disease that commonly involves midline areas of the nasal cavity, oral cavity, and pharynx but may involve the GI tract; b) is a malignant and aggressive disease when involving the GI tract in areas below pharynx; c) usually involves rapidly proliferating malignant NK rather than T<unk> s; d) commonly causes tissue-destructive lesions that are spread through multiple layers of the GI tract; and e) has lesions consisting of rapidly proliferating lymphocytes which express Epstein-Barr virus products, CD56, and one or more of various specific genetic abnormalities (see Genetic abnormalities in ENKTCL-NT). * Monomorphic epithelieotropic intestinal lymphoma (MEITL) (formerly termed Type II enteropathy-associate T-cell lymphoma): Unlike ITCLD-GT, MEITL a) is a highly aggressive lymphoma of the GI tract that usually takes a short, lethal course; b) has lesions in which rapidly proliferating T<unk> s accumulate in the mucosa and epithelium of the GI tract; and c) involves T<unk> s that are CD4-, CD56-, and MAKT+, often express the γδ rather than the αβ T<unk>  receptor, and in rare cases are infected with, and express products made by, the Epstein-Barr virus. * Peripheral T-cell lymphoma subtype peripheral T-cell lymphoma not otherwise specified (PTCL-NOS): Unlike ITCLD-GT, PTCL-NOS a) is a heterogenous disease that typically involves peripheral lymph nodes but only rarely develops in the GI tract and b) is characterized by the rapid proliferation of CD4+ T<unk> s that overexpress either GATA3 or TBX21, have a wide range of characteristic genetic abnormalities (see genetic abnormalities in PTCL, NOS), and in ~30% of cases are infected with, and express products made by, the Epstein-Barr virus. * Celiac disease: A high proportion of patients with CD4+ ITCLD-GT and rare cases of CD8+ ITCLD-GT have been misdiagnosed as having celiac disease. Unlike celiac disease, ITCLD-GT: a) is unresponsive to gluten-free diets: b) is negative for antigens detected in standard celiac disease serology blood tests such as anti-transglutaminase antibodies; c) has infiltrating clonal T<unk> s which do not express HLA-DQ2 or HLA-DQ8 human leukocyte antigens; and d) have lesions populated by mature, slowly proliferating clonal T<unk> s which are CD56- and either CD4+, CD8+, CD4+/CD8+, or CD4-/CD8-. However, rare patients have been inflicted with both celiac disease and ITCLD-GT. * Crohn's disease: Crohn's disease has been diagnosed in cases which were later diagnosed as ITCLD-GT perhaps because some patients with ITCLD-GT have histopathologic features (particularly the presence of granulomas)) that are characteristic of Crohn's disease. Awareness of ITCLD-GT and the histologic, clinical, and endoscopic differences between it and Crohn's disease should point to the proper diagnosis. * Ulcerative colitis: Rare wcases of ITCLD-GT appear to have been diagnosed as ulcerative colitis. Awareness of ITCLD-GT and the histologic, clinical, and endoscopic differences between it and ulcerative colitis should point to the proper diagnosis. * Natural killer<unk>  enteropathy (NKCE): NKCE is an<unk>  disease in which lymphocytes proliferate in the GI tract to cause lesions and symptoms that resemble ITCLD-GT. NKCE differs from ITCLD-GT in that it: a) involves the proliferation of non-clonal NK<unk>  rather than T<unk>  lymphocytes; b) does now show evidence of mesenteric lymph node or other organ involvement; and c) does not progress to a malignant disease.
Indolent T cell lymphoproliferative disorder of the gastrointestinal tract
Foreign body in alimentary tract
Effects of parasitic worms on the immune system
Small intestine neuroendocrine tumor
Autoimmune gastrointestinal dysmotility
Multifocal stenosing ulceration of the small intestine
Gastric antral vascular ectasia
Cystic lesions of the pancreas