Immunohistochemical differentiation of eosinophilic esophageal myositis from eosinophilic esophagitis

Background and Aim Eosinophilic esophagitis (EoE) is a Th2‐mediated allergic disease of the esophageal epithelium, associated with antigen. We previously reported a case series for eosinophilic esophageal myositis (EoEM)—a novel eosinophilic gastrointestinal disorder defined as eosinophilic infiltration localized in the esophageal muscle layer—and diagnosed it by peroral endoscopic muscle biopsy. Here, we investigated the immunopathology of EoEM to differentiate it from EoE. Methods Histological analysis was performed for three cases of EoEM and EoE, respectively. The results were compared with those of two control samples (non‐eosinophilic gastrointestinal disorder full‐layer esophagus). Using immunofluorescence, we analyzed the expression of the chemokine receptor CCR3 and its ligands eotaxin‐1 and eotaxin‐3 to investigate the eosinophilic reaction. Additionally, we determined the expression patterns of desmoglein‐1 in the esophageal epithelium, which shows dysregulated expression in EoE. Results Eosinophil infiltration was observed in the muscle layer (maximum number, 30, 36, 73/high‐power field) and the epithelium (50, 44, 40/high‐power field) for EoEM and EoE, respectively. In EoE esophageal epithelium, the number of eotaxin‐3‐positive epithelial cells was significantly increased together with CCR3‐positive infiltrating cells. However, in EoEM, a number of eotaxin‐1‐positive and eotaxin‐3‐positive myocytes and vascular endothelial cells were increased in the esophageal muscle layer. A significant loss of desmoglein‐1 expression was only observed in EoE, not in EoEM. Conclusions Eotaxin‐1 and eotaxin‐3 expression on the smooth muscle and vessels plays a role in the pathogenesis of EoEM, while EoE shows an epithelial eotaxin‐3‐dominant immunoreaction. Thus, the EoEM immunological pattern displays clear differences from that of EoE.