Consensus diagnostic recommendations to distinguish gastro-oesophageal reflux disease (GORD) from eosinophilic oesophagitis (EoE) by response to a trial of proton pump inhibitors (PPI) unexpectedly uncovered an entity called “PPI-responsive oesophageal eosinophilia” (PPI-REE). PPI-REE refers to patients with clinical and histologic features of EoE that remit with PPI treatment. Recent and evolving evidence, mostly from adults, shows that PPI-REE and EoE patients at baseline are clinically, endoscopically and histologically indistinguishable, and have significant overlap in terms of features of Th2 immune-mediated inflammation and gene expression. Furthermore, PPI therapy restores oesophageal mucosal integrity, reduces Th2 inflammation and reverses the abnormal gene expression signature in PPI-REE patients, similar to the effects of topical steroids in EoE patients. Additionally, recent series have reported that EoE patients responsive to diet/topical steroids may also achieve remission on PPI therapy. This mounting evidence supports the concept that PPI-REE represents a continuum of the same immunologic mechanisms that underlie EoE. Accordingly, it seems counterintuitive to differentiate PPI-REE from EoE based on a differential response to PPI therapy when their phenotypic, molecular, mechanistic, and therapeutic features cannot be reliably distinguished. For patients with symptoms and histologic features of EoE, it is reasonable to consider PPI therapy not as a diagnostic test, but as a therapeutic agent. Due to its safety profile, ease of administration and high response rates (up to 50%), PPI can be considered a first-line treatment, before diet and topical steroids. The reasons why some EoE patients respond to PPI, while others do not, remain to be elucidated.

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