Loss of Tolerance in Long-Term Allergen Immunotherapy: A Case of Late-Onset Systemic Anaphylaxis

This case report documents a rare phenomenon of a serious systemic allergic reaction following nearly five years of ongoing allergen immunotherapy (AIT) in a 19-year-old male patient. The patient, stable on maintenance AIT for sensitization to dust mite, cat dander, and birch pollen, developed acute respiratory distress minutes after a routine injection. Emergency treatment with epinephrine, diphenhydramine, and salbutamol was successful. This case highlights several potential causes, including loss of immune tolerance, immune deviation due to infection, and possible immunomodulating properties of concurrent fluoxetine treatment. It is a reminder that patients on long-term AIT need to continue on follow-up and that drug-AIT interactions are an area for ongoing investigation.