There is currently no reliable, noninvasive biomarker for eosinophilic esophagitis (EoE), a chronic allergic diseases characterized by significant infiltration of eosinophils in the esophagus. Because eosinophils release nitric oxide, levels of exhaled nitric oxide (FeNO) are used routinely for guiding treatment in subsets of patients with asthma. FeNO levels are also elevated in immunological diseases that do not involve the airways. The investigators hypothesize that patients with EoE have elevated nitric oxide concentration in their exhaled breath and that changes in FeNO levels could be used to measure disease activity. The objective of this study is to determine the feasibility of using FeNO as a noninvasive surrogate marker for EoE disease activity. The investigators propose to measure serial exhaled nitric oxide (FeNO) levels on a group of patients with confirmed EoE, before, during and after the course of topical corticosteroid therapy to determine whether the level declines from pre-treatment level in individual patients.

Inclusion Criteria:

• Age 7-65.
• Confirmed diagnosis of EoE. The diagnosis of eosinophilic esophagitis is based upon the presence of characteristic clinical features and large numbers of eosinophils in the esophagus on pathologic examination (≥15 eosinophils per high powered [400x] field in at least one specimen) despite acid suppression with a PPI for one to two months. The criteria also include normal gastric and duodenal mucosal biopsies and the exclusion of other causes. Clinical features in adults include dysphagia, pain and/or history of food impaction. Symptoms in children vary depending in part upon their age: feeding disorders (median age 2.0), vomiting (median age 8.1), abdominal pain (median age 12.0), dysphagia (median age 13.4), and food impaction (median age 16.8).

Exclusion Criteria:

• Use of systemic or inhaled corticosteroids in the preceding 3 months.
• History of doctor-diagnosed asthma, acute or chronic rhinosinusitis.
• History of cirrhosis.
• History of kidney, heart or lung disease.
• Pregnancy

Gastroenterology outpatient clinic