Eosinophilic Esophagitis (EoE) is a chronic inflammatory condition affecting the esophagus, the tube connecting the mouth to the stomach. It is characterized by an accumulation of eosinophils, a type of white blood cell, in the esophageal lining. This immune-mediated disease can lead to various symptoms related to esophageal dysfunction, such as difficulty swallowing, vomiting, and chest pain. Biopsies are a fundamental tool in both diagnosing and managing EoE.
Why Biopsies Are Essential for Diagnosis
Biopsies are essential for definitively diagnosing EoE, as symptoms and endoscopic findings alone are insufficient. While an upper endoscopy allows a healthcare professional to visually inspect the esophageal lining for signs like rings, furrows, or swelling, these visual cues can also be present in other conditions or sometimes be absent entirely in EoE patients. Tissue analysis is therefore required to confirm eosinophilic inflammation.
During an upper endoscopy, a thin, flexible tube is inserted down the throat, enabling the physician to view the esophagus. Small tissue samples, known as biopsies, are then collected from the esophageal lining. Current guidelines recommend taking multiple biopsies, typically at least six, from different areas of the esophagus, including the proximal, mid, and distal sections. Multi-site sampling is important because eosinophil infiltration in EoE can be patchy.
Deciphering Eosinophil Counts
The “numbers” in an EoE biopsy refer to the count of eosinophils per high-power field (HPF). After biopsies are taken, a pathologist examines them under a microscope to identify and quantify these white blood cells. A high-power field is a standardized unit of area viewed through the microscope.
The accepted diagnostic threshold for EoE is 15 or more eosinophils per HPF in at least one esophageal biopsy sample, though eosinophils alone do not confirm EoE, as other conditions like gastroesophageal reflux disease (GERD) can also cause eosinophilia in the esophagus. Pathologists also look for other microscopic features that support an EoE diagnosis, such as eosinophil microabscesses (clusters of at least four eosinophils), basal zone hyperplasia (thickening of the basal layer of the esophageal lining), and dilated intercellular spaces. These additional findings, along with the eosinophil count and clinical symptoms, help differentiate EoE from other causes.
Beyond Diagnosis: Biopsies in Treatment Monitoring
Beyond initial diagnosis, biopsies play a significant role in monitoring EoE treatment effectiveness and disease activity. After a patient begins therapy (e.g., dietary changes, PPIs, topical steroids), follow-up endoscopies with biopsies are performed. These subsequent biopsies help determine if eosinophil counts have decreased, indicating a positive response.
The goal of treatment is to achieve “histologic remission,” meaning reducing the eosinophil count to a low level, typically below 15 eosinophils per HPF. While symptoms may improve with treatment, relying solely on symptom resolution is not enough to confirm disease control. Histologic remission is considered a more objective measure of treatment success, as symptoms and endoscopic appearance can remain unchanged even when microscopic inflammation has improved.
Factors Influencing Biopsy Results
Several factors can influence eosinophil counts in a biopsy, potentially affecting interpretation. Prior use of medications (e.g., proton pump inhibitors or swallowed corticosteroids) can lower eosinophil counts, even if underlying EoE inflammation is present. This can lead to a false negative or a misleadingly low count, making diagnosis or assessment of disease activity harder.
The patchy nature of EoE inflammation means eosinophils are not uniformly distributed throughout the esophagus. If biopsies are not taken from affected areas, it can result in a false-negative diagnosis. Additionally, recent dietary changes, particularly elimination diets, before a biopsy can reduce eosinophil counts, masking the true extent of inflammation. Healthcare providers consider these influencing factors and correlate biopsy findings with a patient’s symptoms and clinical history for a comprehensive assessment.