Adults with FPIES have significantly higher rates of atopic diseases. Allergic rhinitis, asthma, atopic dermatitis are conditions that occur more frequently in patients with FPIES.

Increased rates of classic food allergy (IgE mediated), compared with adults without FPIES have also been reported. Besides eosinophilic esophagitis is also a common condition associated with FPIES. These observations suggest a common predisposition and/or shared disease mechanism.

Urticaria has been observed more commonly than in the general population..

A slight major incidence of gastrointestinal diseases has also been observed in adults with FPIES, in addition to eosinophilic esophagitis, diseases such as inflammatory bowel disease, irritable bowel syndrome or celiac disease have a higher prevalence than in the general population.

Otherwise many conditions can mimic acute episodes of FPIES. In most patients, the first episodes of FPIES are misdiagnosed as viral gastroenteritis or food poisoning, but subsequent recurrent episodes confirm a relationship to specific foods.

In the case of patients that have FPIES symptoms triggered by fish,  anisakiasis must be ruled out. Anisakis simplex is a worm that infects humans after eating the raw or undercooked fish.  Symptoms include acute epigastric or severe abdominal pain, nausea, vomiting and abdominal distension. Diarrhea may also develop. These symptoms usually overlap with the manifestations of acute FPIES, however allergic reactions ranging from mild urticaria to bronchoconstriction, angioedema, and anaphylactic shock usually occur in anisakiasis, but not in FPIES. The recurrence of episodes in subsequent fish ingestion and the absence of specific IgE to anisakis in serum or skin test, rules out the diagnosis of anisakiasis and support the diagnosis of FPIES.

In classic food allergies, digestive symptoms may be present such as abdominal pain, vomiting, diarrhea but they are associated to skin symptoms such as hives or angioedema (rapid swelling of deep layers of the skin) or asthma. These symptoms are absent in FPIES.

Celiac disease is an immunologic disorder caused by the ingestion of gluten, that may debut both in children and in adults. Symptoms include abdominal pain, diarrhea and poor weight gain. Patients with Fpies triggered by cereals may have similar symptoms, but serologic test and biopsy will confirm or rule out celiac disease.

In adults with symptoms of FPIES induced by milk, differential diagnosis with lactose intolerance may be challenging, as they also share common clinical features. A normal hydrogen breath test and frequent presence of vomiting supports the diagnosis of FPIES.

Irritable bowel syndrome (IBS) is a common chronic condition of the digestive system. Its primary symptoms are abdominal pain and changes in bowel habits (constipation and/or diarrhea). In some uncommon cases of multiple-food FPIES, triggered by foods  that are consumed regularly like milk, egg or meat, differential diagnosis with IBS is difficult. A diet diary and oral food challenge are required for diagnosis. However collaboration with gastroenterology service is essential  in these cases to rule out other processes.

Inflammatory bowel disease includes conditions that cause inflammation of the digestive tract, including Crohn’s disease and ulcerative colitis (UC) in which  the immune system is implicated. Symptoms can be mild or severe and consist of diarrhea, abdominal pain, rectal bleeding, weight loss… No relationship with  foods is observed, however some patients complain that certain foods seem to worse symptoms such as milk, or other dairy foods. In patients with multiple-food FPIES suspicion, these conditions must be ruled out previously by gastroenterologists that will perform a colonoscopy and biopsy.