**2. Diagnosis**

EoE is a clinico-pathological disease characterized by symptoms related to esophageal dysfunction. Up to now, esophageal biopsies have been essential for making a diagnosis. For optimal pathological evaluation, multiple biopsies from the proximal and distal esophagus should be obtained and evaluated for a variety of pathological features, the most characteristic being an eosinophil-predominant inflammation with a minimum threshold of 15 eosinophils/high power field (hpf). However other accompanying findings reinforce the diagnosis and should also be noted by the pathologist. These include: eosinophilic microabscesses, surface layering of eosinophils, extracellular eosinophilic deposits, basal cell hyperplasia, intercellular edema, and lamina propria fibrosis (Furuta et al., 2007).

The effects of EoE are isolated to the esophagus; therefore, eosinophilic inflammation should be absent from both gastric and duodenal biopsy samples (Lucendo, 2010). Furthermore, other causes of esophageal eosinophilia should be excluded, specifically gastroesophageal reflux disease (GERD). This can effectively be excluded if there is a normal pH-metry or if eosinophils persist after treatment with full doses of proton pump inhibitors (PPI). However, the prevalence of patients suffering from both EoE and GERD make the PPI trial the method of choice for diagnosing EoE in these cases (Molina-Infante et al., 2009).
