Primary eosinophilic disorders of the gastrointestinal tract

Eosinophils are important effector cells of the innate immune system. Eosinophilic infiltrative disorders of the gastrointestinal tract, though recognised for decades, have recently witnessed a resurgence of interest, particularly for oesophageal disease. A more comprehensive basis for eosinophilic infiltration and activation has identified interleukin 5 (IL5) as a key cytokine for the differentiation and proliferation of eosinophils, while eotaxins promote the recruitment of mature eosinophils to the gut. When activated, eosinophils release multiple cytotoxic agents and immunomodulatory cytokines, resulting in local inflammation and tissue damage. Although eosinophils normally convey a defence against unwanted interlopers such as parasites, in the absence of such inciting agents, their accumulation and activation can elicit the primary infiltrative disorders of the gut: eosinophilic oesophagitis, gastroenteritis and colitis. Diagnosis of these disorders is dependent on the clinical presentation, endoscopic findings (particularly for eosinophilic oesophagitis), and most importantly, histological confirmation. Dietary modifications and topical corticosteroids are first-line treatments for eosinophilic oesophagitis. Systemic corticosteroids are the mainstay of treatment for eosinophilic gastroenteritis; surgery may be required depending on the layer of mucosa involved. Eosinophilic colitis most often occurs in infants; removal of the causative allergen usually results in a complete response. Steroids may be required for older children/adolescents or adults. This review summarises current knowledge on the trafficking of eosinophils to the gastrointestinal tract and the clinical management of the primary disorders of eosinophilic oesophagitis, eosinophilic gastroenteritis and eosinophilic colitis.