Chronic Endometritis: Key Causes and Clinical Observations

Chronic endometritis is a persistent inflammation of the endometrial lining that often goes unnoticed due to its subtle or absent symptoms. Despite its links to infertility, recurrent pregnancy loss, and failed embryo implantation, it remains underdiagnosed.

Research indicates that microbial imbalances, immune dysregulation, and hormonal influences contribute to this condition. Understanding these factors is crucial for improving diagnosis and treatment.

Clinical Observations

Patients with chronic endometritis frequently exhibit nonspecific or no symptoms, complicating detection. When symptoms occur, they may include abnormal uterine bleeding, pelvic discomfort, or persistent leukorrhea, though these signs are often mild and overlooked. A study in The Journal of Minimally Invasive Gynecology found that nearly 60% of diagnosed women had no overt symptoms, contributing to delayed diagnosis, particularly in those seeking fertility evaluations after implantation failures or pregnancy loss.

Gynecological exams rarely reveal definitive findings, but some patients display cervical tenderness or endometrial thickening on transvaginal ultrasound. A study in Human Reproduction reported a higher prevalence of endometrial fluid accumulation on ultrasound in women with unexplained infertility and chronic endometritis. However, imaging alone is unreliable, as many cases show no abnormalities.

Menstrual irregularities, especially prolonged or intermenstrual spotting, have been observed. A Fertility and Sterility study found that 30% of women with histologically confirmed chronic endometritis reported atypical bleeding patterns. Some patients also experience mild pelvic discomfort, often misattributed to conditions like endometriosis or pelvic inflammatory disease, further complicating recognition.

Microbial And Inflammatory Factors

The endometrial environment maintains a delicate microbial balance, but disruptions have been increasingly linked to chronic endometritis. Next-generation sequencing has identified an overrepresentation of Enterococcus faecalis, Streptococcus spp., Escherichia coli, and Ureaplasma urealyticum in affected individuals. A study in The American Journal of Obstetrics and Gynecology found that women with chronic endometritis exhibited reduced Lactobacillus dominance, with a concurrent rise in bacteria known for their inflammatory potential. This shift contributes to chronic low-grade inflammation, potentially impairing embryo implantation.

Bacterial colonization alone does not cause chronic endometritis; rather, the sustained inflammatory response perpetuates the condition. Histological examinations reveal stromal edema, plasma cell infiltration, and increased vascularity, indicative of persistent immune activation. Bacterial lipopolysaccharides and other pathogen-associated molecular patterns stimulate toll-like receptors on endometrial epithelial cells, triggering cytokine release. Elevated levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) have been linked to impaired endometrial receptivity. A meta-analysis in Reproductive Sciences found a correlation between elevated TNF-α levels and recurrent implantation failure, suggesting chronic inflammation disrupts pregnancy outcomes.

Alterations in the local microbiome may also weaken the endometrial barrier, allowing deeper bacterial invasion. Research in The Journal of Infectious Diseases found that Escherichia coli and Enterococcus faecalis strains from chronic endometritis patients form biofilms, which contribute to persistent infection and antibiotic resistance. Biofilms shield bacterial communities from immune clearance and antimicrobial agents, potentially explaining frequent recurrence and the need for prolonged or combined antibiotic regimens.

Histological Features

Microscopic examination reveals architectural and cellular changes characteristic of chronic endometritis. The most defining marker is plasma cell presence within the endometrial stroma. Unlike lymphocytes, which are common in normal endometrial tissue, plasma cells indicate prolonged inflammation. These cells can be difficult to identify using routine hematoxylin and eosin (H&E) staining, often requiring immunohistochemical staining for CD138, a plasma cell-specific marker. Research in Modern Pathology showed CD138 staining significantly enhances diagnostic sensitivity.

Beyond plasma cell infiltration, chronic endometritis is associated with stromal alterations. Edematous expansion of the stromal matrix contributes to a loose, disorganized structure, often accompanied by increased fibroblast activity, suggesting ongoing tissue repair. Glandular changes, including irregular spacing and mild architectural distortion, have been observed. Studies in Diagnostic Pathology noted that affected glands may exhibit pseudostratification of epithelial nuclei, resembling hyperplasia but lacking mitotic activity.

Vascular abnormalities are also common. Capillary congestion and focal hemorrhages reflect localized blood flow disruptions. Increased microvascular density, possibly a compensatory response to chronic inflammation, has been reported. A study in The Journal of Pathology found that endometrial biopsies from chronic endometritis patients exhibited increased vascular endothelial growth factor (VEGF) expression, suggesting excessive neovascularization may impair implantation.

Hormonal And Immune Interplay

The endometrial lining undergoes cyclical changes driven by hormonal fluctuations, and disruptions in this balance contribute to chronic endometritis. Estrogen and progesterone regulate endometrial proliferation, differentiation, and immune tolerance, but inflammation can interfere with these hormonal signals.

Progesterone resistance, observed in several endometrial disorders, has been linked to impaired tissue remodeling and receptivity. Studies have identified reduced expression of progesterone receptor isoforms in chronic endometritis patients, suggesting inflammation disrupts the hormone’s role in preparing the endometrium for implantation.

Estrogen, while essential for endometrial regeneration, also modulates immune activity. Inflammatory conditions can alter estrogen metabolism, sustaining proliferative signaling and disrupting homeostasis. Elevated estradiol levels have been shown to enhance pro-inflammatory mediator expression, perpetuating tissue dysfunction. This hormonal-immune feedback loop may contribute to the chronic nature of the condition.

Diagnostic Evaluations

Since chronic endometritis often lacks clear symptoms or imaging findings, definitive diagnosis relies on targeted endometrial tissue assessments. Endometrial biopsy is the most reliable method, allowing histological and microbiological examination. Pipelle aspiration is commonly used, offering an adequate specimen with minimal discomfort. Studies show this minimally invasive technique has a high diagnostic yield, particularly when combined with specialized staining to detect plasma cells. Immunohistochemical staining for CD138 improves the identification of plasma cell infiltration, enhancing diagnostic accuracy.

Advances in molecular diagnostics have refined detection strategies. Polymerase chain reaction (PCR)-based assays and next-generation sequencing enable precise identification of microbial imbalances. These methods offer greater sensitivity than conventional cultures, which often fail to isolate fastidious or biofilm-forming bacteria. Studies show molecular sequencing can uncover a broader spectrum of bacterial species, providing a more comprehensive view of microbial dysbiosis.

Hysteroscopy has also gained recognition as a valuable diagnostic tool, allowing direct visualization of endometrial abnormalities such as focal edema, micropolyps, or hemorrhagic spots. When combined with targeted biopsy, hysteroscopy improves diagnostic accuracy, particularly in cases where histological findings alone are inconclusive.

Underexplored Biological Dimensions

Despite increasing recognition of chronic endometritis as a contributor to reproductive dysfunction, several biological aspects remain understudied. One emerging area of interest is the role of the endometrial extracellular matrix (ECM) in sustaining inflammation. The ECM provides structural support, but persistent inflammation can alter its composition, leading to excessive fibrotic protein deposition. These changes may impair tissue remodeling and contribute to suboptimal implantation conditions. Recent research suggests chronic endometritis may induce a fibrotic response similar to that seen in other chronic inflammatory diseases, potentially explaining its persistence even after antibiotic treatment.

Another underexplored area is the interplay between neuroimmune signaling and endometrial function. The uterus contains sensory and autonomic nerve fibers that regulate vascular tone and tissue repair. Emerging evidence suggests chronic inflammation alters neuropeptide expression, affecting endometrial sensory signaling and contributing to pain symptoms. Additionally, neuroimmune dysregulation may influence local immune cell recruitment, perpetuating inflammation. Understanding these mechanisms could lead to new therapeutic approaches, particularly for antibiotic-resistant or recurrent cases.