Chronic endometritis (CE) is a local inflammatory disease characterized by unusual plasmacyte infiltration in the endometrial stromal areas. CE has been neglected in gynecologic practice, as it is a less symptomatic benign disease that requires demanding and time-consuming histopathologic examinations for the definite diagnosis. Recent studies, however, suggest the association of CE with infertility and obstetric and neonatal complications. In this review article, we aimed to update the knowledge on epidemiology, etiology, and pathogenesis of CE as well as discuss its clinical management from diagnosis to treatment.

Chronic endometritis is a common gynecological pathological condition and more often asymptomatic than ever expected. There was no menstrual cycle-dependent fluctuation in its occurrence.

Chronic endometritis is often identified in the patients with unexplained infertility, and is histopathologically characterized by infiltration of plasmacytes within the endometrial stroma. In parallel with stromal plasmacyte infiltration, the endometrial functional layer in chronic endometritis is invaded by B cells, which are a rare leukocyte subset residing within the basal layer in the nonpathological endometrium. In this study, we investigated the molecular expression underlying this unusual increase of B cells in chronic endometritis. Twenty-two out of 76 infertile patients were diagnosed with chronic endometritis from the stromal plasmacyte infiltration, and the endometrium contained numerous stromal B-cell aggregates and glandular single B cells. However, the other major leukocyte subsets, including T cells, natural killer cells, macrophages, and neutrophils were comparable in densities in chronic endometritis and nonpathological endometrium. The microvascular endothelium showed immunoreactivity to adhesion molecule selectin E and chemokine CXCL13 along with immunoreactivity to CXCL1 in the glandular epithelium in chronic endometritis, but not in the nonpathological endometrium. Lipopolysaccharide significantly induced surface selectin E expression and CXCL13 secretion in uterine microvascular endothelial cells, and CXCL1 secretion in endometrial epithelial cells in vitro. These findings indicated that the aberrant local microenvironment triggered possibly by bacterial infection has a role in selective extravasation of circulating B cells in chronic endometritis.

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Chronic endometritis (CE) is an unusual endometrial inflammation characterized by stromal plasmacyte infiltration. CE is easily missed due to its subtle symptoms and demanding histopathological examinations. Although the immunohistochemistry for the plasmacyte marker CD138 has facilitated the detection of endometrial stromal plasmacytes, the accuracy and biases of this method for CE diagnosis remain poorly understood. The aim of this study was to investigate the inter- and intra-observer variability in the immunohistochemical detection of stromal plasmacytes in the human endometrium. A total of 80 CE and 20 non-pathological archival hematoxylin-stained endometrial preparations with or without immunostaining for CD138 were evaluated independently by two experienced observers and two inexperienced observers. Endometrial stromal plasmacytes in unit areas were counted in the hematoxylin-stained and CD138-immunostained preparations. Each preparation was subdivided into 11 categories by every five plasmacyte counts. The second evaluation was performed four weeks after the first evaluation. The immunohistochemical detection method was superior to conventional histopathological evaluation in both the inter- and intra-observer agreement, irrespective of the experience level of the observers. The linear weighted κ coefficient for intra-observer agreement was higher in the experienced observers than in the inexperienced observers. The inter-observer agreement among the four observers by the immunohistochemical detection method was similarly good between the first and second evaluation. There was no significant inter- or intra-observer variability in the paired comparison of the individual samples. These findings validate the use of immunohistochemistry for CD138 as an accurate and less biased diagnostic tool for CE.