Diagnosis
The diagnoses of NKCE and LG depends on clinical and pathological findings indicating that the two diseases: a) are indolent and non-malignant; b) usually manifested by mild, vague, or no symptoms; c) localize to the GI tract without involvement of the head, neck, or organs such as the liver and spleen; d) consist of one or more lesions localized primarily to the lamina propria of the esophagus, stomach, small intestine, and/or large intestine (for NKCE} or to the stomach (for LG); and e) involve lesions which contain medium-to large-sized, atypical, and non-clonal lymphocytes that are activated NK cells (see Pathophysiology section) which proliferate at moderately rapid rates (as gauged by, e.g. analysis of their Ki-67 protein levels), lack evidence of Epstein-Barr virus infection, gene mutations, or chromosome abnormalities, and show little evidence of centering around, and destroying, blood vessels. Differential diagnosis
In early studies, aggressive chemotherapy with or without bone marrow translanton and gastric resections were used to treat NKCE and LG, respectively, based on the assumptions that these diseases were malignant. Since there was no evidence that these treatments influenced the underlying disease and since NKCE and LG are essentially benign disorders, they must be distinguished from the malignant diseases which they mimic. Three malignant or potentially premalignant diseases which can closely resemble NKCE and LG along with some clinical and laboratory findings which differentiate them from NKCE and LT are:

Extranodal NK/T cell lymphoma, nasal type: This disease can closely mimic NKCE and, to a lesser extent, LG.
Natural killer cell enteropathy, also termed  NK cell enteropathy (NKCE), and a closely related disorder, lymphomatoid gastropathy (LG), are non-malignant diseases in which one type of lymphocyte, the natural killer cell (i.e. NK cell), proliferates excessively in  the gastrointestinal tract (GI tract). This proliferation causes red, sore-like spots, raised lesions, erosions, and ulcers in the mucosal layer surrounding the GI tract lumen. Both disorders cause either no or only vague symptoms of GI tract disturbances such as nausea, vomiting, and bleeding.In 2006, a persistent but apparently benign disease that involved the proliferation of NK cells at multiple sites throughout the intestines was described. This disorder appeared similar to and easily mistaken for a highly malignant disease, extranodal NK/T-cell lymphoma, nasal type. In 2010, a similarly non-malignant disorder that involved the proliferation of NK cells in the stomach was described. The disease mimicked gastrointestinal lymphomas. Since these first descriptions, several case series and case reports have been published on these enteropathies.The two NK cell proliferation diseases have been termed NK cell enteropathy and lymphomatoid gastropathy with NKCE being seen mostly in the United States and Korea and LG being seen mostly in Japan. Besides this geographical difference, the only other critical difference between the two diseases is that the lesions in NKCE occur in the small intestine, colon, stomach, and/or esophagus while those of LG are limited to the stomach.