An esophageal prick test, in which allergens are injected directly into the esophageal mucosa, appears to identify individuals with esophageal sensitization, researchers report in the January issue of Gastroenterology.
In patients with eosinophilic esophagitis (EoE), food allergens are believed to induce an inflammatory response that can make swallowing and eating a challenge.
Identifying and eliminating foods that cause this reaction can be effective. However, skin tests and measurement of serum levels of immunoglobulin E do not always identify foods that trigger this reaction, possibly because the eosinophilic inflammation is restricted to the esophagus. Also, symptoms do not always correlate with disease activity.
Marijn J. Warners et al developed an esophageal prick test, in which the esophageal mucosa is challenged by local injection of allergen extracts (see video). They tested to see whether it could identify individuals with esophageal sensitization.
During endoscopy, 0.2 mL of 6 diluted allergen extracts (wheat, milk, soy, and 3 allergens based on the patients’ history), a negative control (0.9% NaCl), or a positive control (3.4 μg/mL histamine diluted in 0.9% NaCl) were injected into the esophagus of 8 patients with EoE and 3 patients without EoE (controls).
Local responses were recorded up to 20 minutes. A second endoscopy was performed after 24 hours to evaluate delayed responses and to sample 4 biopsy specimens, proximal from the injection sites, to evaluate histologic disease activity.
During the first endoscopy, an intense acute response (characterized by complete luminal obstruction and blanching of the mucosa at the injection site) was observed within 2 minutes after injection of soy (n = 2), banana, apple, oats, or hazelnut in 5 of 8 patients.
The 2 other patients had a delayed wheal or flare reaction. No responses were observed in controls.
Of the 48 allergens injected (6 allergens given to 8 patients), 8 allergens induced a local esophageal response, regardless of the patients’ histologic disease activity (≤10 eosinophils/high-powered field).
Six patients experienced symptoms of food impaction within minutes after ingestion of 1 (n = 3), 2 (n = 2), or 4 (n = 1) culprit food(s). Of these 11 suspicious foods, 7 (63%) corresponded with sensitizations identified through the esophageal prick test, 2 (18%) with skin-prick test sensitizations, and 4 (36%) with serum level of IgE.
Warners et al conclude that esophageal mucosal food allergen injections induce acute and/or delayed responses in patients with EoE but not controls. Compared with skin-prick tests and measurements of serum IgE, the sensitization patterns identified by the esophageal prick test had a higher level of correlation with patients’ clinical suspicion of culprit foods.
How do these allergens cause the obstruction and blanching of the mucosa observed? Warners et al state that the endoscopic view appears similar to that of distal esophageal spasms and type 3 achalasia, indicating spastic contraction. Activated mast cells can increase smooth muscle contractions and might initiate this response. These spastic episodes might coincide with acute impaction after ingestion of certain foods. Alternatively, the narrowing and blanching might result from the esophageal edema caused by the release of factors from mast cells that increase vascular permeability.
The authors propose that pathogenesis of EoE involves IgE-mediated reactions, responsible for esophageal dysmotility and acute food impactions, and delayed non-IgE mediated reactions, which induce T-helper 2 cell-mediated, chronic, eosinophil-predominant inflammation.
The esophageal prick test might be developed to guide elimination diets.