Number and distribution of eosinophils and lymphocytes in the Japanese pediatric gastrointestinal tract: in search of a definition for “abnormally increased eosinophils”

Background Primary eosinophilic gastrointestinal disorders (EGIDs) constitute chronic allergic inflammation. The number of eosinophils is one of the diagnostic criteria; more than 20 eosinophils per high-power field (HPF) in the gastrointestinal (GI) tract are considered abnormal in Japan. However, the quantity of eosinophils considered normal varies according to anatomical location and geographical region; such values have not been reported in Japanese pediatric patients, nor have the numbers of lymphocytes in the normal pediatric stomach. To establish a reference for defining diagnostic criteria for EGIDs, we evaluated the number of eosinophils in the normal Japanese pediatric GI tract. Methods We examined 131 biopsy cases without significant clinical history, endoscopic abnormality, or histological abnormality. Immunohistochemical analysis of CD3 and CD20 was performed. Results The mean eosinophil density was highest in the cecum (49.5 ± 22.4 per HPF). Counts of more than 20 eosinophils per HPF were observed in the duodenum [bulb (20.0 ± 9.6) and second portion (30.0 ± 15.8)], terminal ileum (38.3 ± 22.7), cecum (49.5 ± 22.4), ascending colon (42.3 ± 25.3), transverse colon (29.4 ± 17.0), and descending colon (32.2 ± 17.9). Counts of fewer than 10 eosinophils per HPF were observed in the stomach and rectum; a count of fewer than one eosinophil per HPF was observed in the esophagus. More than 100 CD3-positive T cells per HPF were observed in the stomach. Conclusions The mean numbers of eosinophils in the bowel were greater than 20 per HPF. For Japanese pediatrics, the current threshold eosinophil count should be revised.