Monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL) is a new clinical entity that was reclassified from enteropathy-associated T-cell lymphoma in the 2016 WHO classification. An 83-year-old man with fever and diarrhea was referred to our hospital because of free air in the abdominal cavity and wall thickening of the large intestine on CT. Colonofiberscopic examination revealed mucosal edema and multiple ulcers at the sigmoid colon, splenic flexure, and transverse colon. Histopathological examination of the mucosal biopsy specimen demonstrated dense infiltration of small lymphocytes with nuclear atypia, some of which exhibited intraepithelial invasion. Immunohistologically, these lymphocytes were positive for CD3, CD56, and perforin. Regarding CD3 expression, the antigen was found to only be expressed in the cytoplasm and not on the surface membrane on flow cytometric analysis. PCR examination of the T-cell receptor (TCR) gene revealed monoclonal gene rearrangements of TCR-γ and TCR-β. Based on these findings, a diagnosis of colonal MEITL with cyCD3 expression at Lugano clinical stage 1 was made. After conservative management of the peritonitis, we treated the patient with CHOP and DeVIC regimens, but he developed progressive disease and died. The cyCD3 expression in MEITL may be novel, suggesting a thymocyte origin of the tumor cells.

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A diagnosis of acute monocytic leukemia (AML-M5) based on α-naphthyl butyrate esterase (α-NB) staining has some problems, because AML-M5 leukemic cells often show weak or faint positivity on α-NB staining. In these situations, some cases of AML-M5 tend to be misdiagnosed as AML-M0. Therefore, we evaluated the significance of weak or faint α-NB staining in AML-M5 diagnosed by flow cytometry (FCM). Nineteen AML cases in which leukemic cells were negative for naphthol AS-D chloroacetate esterase staining were studied. For FCM, we defined leukemic cells as having a monocytic nature when more than 10% of the leukemic cells were positive for at least one of the following antigens: CD4, CD11c, CD14, and CD64. The monocytic nature determined by FCM was consistent with positive or weak positivity on α-NB staining. Five of 6 cases in which leukemic cells exhibited faint positivity for α-NB staining could be diagnosed as AML-M5 by FCM, while negative α-NB staining was consistent with a diagnosis of AML-M0. These results suggest that AML-M5 should be taken into consideration even when leukemic cells are faintly positive for α-NB staining.

Regarding viral infection of intestinal mucosa, there have been only a few studies on limited diseases, targeting a few herpes family viruses. In this study, we analyzed 12 kinds of DNA viruses including 8 species of herpes family viruses in the gastrointestinal mucosa of patients with hematologic malignancies, inflammatory bowel diseases, collagen diseases, or other miscellaneous forms of gastroenteritis using the multiplex virus PCR assay, which we recently developed. The virus PCR assay yielded positive results in 63 of 102 patients; Epstein-Barr virus (EBV) was the most frequently detected, followed by cytomegalovirus (CMV), human herpes virus 6 (HHV-6), HHV-7, parvovirus B19, and herpes simplex virus type 1. The frequencies of viral detection in the 4 diseases were similar involving these 6 viruses. Regarding CMV colitis, the multiplex virus PCR assay was superior to the immunohistopathologic method in detecting CMV. All viruses were more efficiently detected in the mucosa than in the blood in individual patients. These results suggest that CMV, EBV, and HHV-6 were commonly detected in the gastrointestinal mucosa of patients with these 4 diseases, and our multiplex virus PCR assay was useful for the early diagnosis of gastrointestinal virus infection, especially CMV colitis.

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