**4. Pathology**

The major features (**Figure 2**) include infiltration of numerous eosinophils (usually >15 per high power field) into the squamous epithelium, layering of eosinophils on the surface layer and eosinophilic microabscess formation (clusters of ≥4 eosinophils). Often necrotic squamous cells are also seen on the surface layer [11]. Minor features include chronic inflammatory infiltrate into the lamina propria with fibrosis of the lamina propria [12], hyperplasia of muscular layers and basal epithelial cells with lengthening of lamina propria papillae, and intercellular edema. One study showed plenty of IgG4containing plasma cells in the lamina propria [13]. The pathological changes are patchy in distribution, and generally affect the whole

**Figure 2.** *HE staining showing esophageal eosinophilia.*

length of the esophagus. None of the histologic findings is specific for eosinophilic esophagitis. Esophageal eosinophilia can be found in a variety of disorders including gastroesophageal reflux disease (GERD), eosinophilic gastroenteritis, hypereosinophilic syndrome, Crohn's disease, connective tissue diseases, drug hypersensitivity, parasitic and fungal infections and achalasia. In clinical practice, the real challenge comes to differentiate EoE from GERD [14]. Eosinophilic degranulation is seen more profoundly in EoE than in GERD biopsy specimen [15]. In EoE, the eosinophilic inflammation extends beyond mucosa into the submucosa and muscularis propria.
