Abstract
Food protein-induced enterocolitis syndrome (FPIES) is a non-immunoglobulin E (IgE)-mediated food allergy. IgE sensitization to the causative food is often not observed, and the rate of sensitization to other common foods is not exceptionally high. This report discusses the case of a boy being followed up for FPIES due to egg yolk, who developed a buckwheat allergy during the disease. The boy was seen at the age of nine months because he vomited multiple times three hours after consuming egg yolk. Blood test results were IgE 32 IU/mL, egg white 3.78 UA/mL, and ovomucoid <0.1 UA/mL. The diagnosis was egg yolk FPIES, and a stepwise challenge test was performed; egg yolk FPIES was in remission by the age of three years. However, he developed hives after eating buckwheat when he was two years and two months old; a blood test was performed, which showed IgE 981 IU/mL and buckwheat >100 UA/mL. Initially, his condition was a non-IgE FPIES, showing that even if a patient does not have other IgE-mediated food allergy complications, it is possible to develop a new food allergy during the disease. This case demonstrates that in patients with FPIES, it is important to regularly evaluate blood tests and intake of typical causative foods for allergies.