Food ALergies

FPIES: Expanding the Differential for Hypotension in the Pediatric Patient


An 8-month-old male, full term, infant with no significant past medical history presents to the ED for nausea, vomiting, and non-bloody diarrhea for the past several hours. His family has slowly been introducing new foods into his diet. There are no known sick contacts. He is well-appearing, hemodynamically stable, and tolerating PO in the ED. After some observation, the patient was discharged with the diagnosis of viral gastroenteritis.

Six days later, the same patient presented with profuse vomiting, diarrhea, and profound lethargy. He was found to be tachycardic and hypotensive. He was taken to the critical care area for altered mental status, unstable vital signs, and undifferentiated shock. His exam was notable for lethargy, pallor, and a distended abdomen. Initial labs showed a metabolic acidosis, eosinophilia, and thrombocytosis. Stool studies and UA were unrevealing. Abdominal plain films were normal.


FPIES - What is it?

As many ED practitioners are aware, food allergies are common in the first 2 years of life, with a prevalence cited between 1-10% of the population. Most food allergies are IgE-mediated hypersensitivity reactions. Food protein-induced enterocolitis (FPIES) is a syndrome characterized by a severe non-IgE mediated food hypersensitivity reaction. FPIES is important to keep on the differential as the syndrome often goes unrecognized or is misdiagnosed at the initial (or subsequent) presentation. (1)

FPIES is characterized by profound and repetitive vomiting, and occasionally diarrhea, 1-4 hours after exposure to the causal protein. In the acute setting, this can manifest as dehydration and lethargy. More than 15% of FPIES patients will require admission for hemodynamic instability secondary to dehydration. In the chronic setting, pediatric patients can present as failure to thrive and/or unexplained weight loss. The most common food triggers in FPIES are cow milk's and soy. FPIES may be induced by solid food, including grains, meat and poultry, eggs, vegetables and fruit, seafood, and legumes. (1,3)

Though the underlying mechanism of FPIES is not clearly understood, it differs from other allergen mediated reactions as it is not triggered by an (IgE)-mediated hypersensitivity. Preliminary research indicates that there is inflammation within the lamina propria and epithelium in both the small and large intestine secondary to increased tumor necrosis factor-alpha (TNF-α) expression by activated T cells. Downstream, this causes increased intestinal permeability which contributes to pathogenesis of FPIES. (4, 8)

Figure A.

Figure A.


Patients with acute presentations tend to be sicker and may develop pallor, hypotension/shock, and/or hypothermia. Failure to thrive and weight loss are seen in patients with chronic FPIES.

  • Lethargy (70%)

  • Pallor (70%)

  • Dehydration

  • Hypotension (15%)

  • Hypothermia (25%)

  • Abdominal distension


Labs often reveal anemia, hypoalbuminemia, and an elevated white blood cell count with a left shift. Eosinophilia is often seen in chronic FPIES. Thrombocytosis was found in 65 percent of acute FPIES. Metabolic acidosis (mean pH 7.03) and methemoglobinemia have been reported in both acute and chronic FPIES. Transient methemoglobinemia was reported in about one-third of acute FPIES infants with some requiring methylene blue treatment. Methemoglobinemia may be caused by severe intestinal inflammation and reduced catalase activity resulting in increased nitrites. (5)

Diagnostic imaging studies are not part of the standard FPIES workup, but some older studies have analyzed trends. Although findings are nonspecific, it is important to be familiar with them as often these infants get imaging as part of their workup.

Findings include:

  • Air fluid levels

  • Nonspecific narrowing and thumb-printing of rectum and sigmoid colon

  • Thickening of plicae circulares in duodenum and jejunum

  • Excess luminal fluid

  • Rarely intramural gas (which can lead to misdiagnosis of NEC)

Resolution of radiographic abnormalities after dietary restriction has been documented. (1, 3, 5)


Given the clinical picture of FPIES is nonspecific, the ED physician can arrive at the diagnosis more quickly by obtaining a brief dietary history. This especially holds true if the patient has been seen multiple times in the ED prior for similar complaints. In infants, the causes of acute repetitive vomiting and severely altered mental status includes a broad differential diagnosis. Sepsis, infectious gastroenteritis, head injury, toxicologic, gut malrotation, intussusception, NEC, pyloric stenosis, as well as other metabolic and cardiogenic causes can present similarly. In patients with such symptoms, allergy as a cause is sometimes not considered by ED physicians. Diagnosis of FPIES is based on the recognition of clinical manifestations, exclusion of alternative causes, and a physician-supervised oral food challenge (OFC). Diagnosis is often made in the inpatient or primary care setting, and is based on presence of a major criterion as well as three minor criteria as seen below.

Below are some quick and dirty rules to differentiate FPIES from other diagnoses:

Food protein-induced proctocolitis: Infants are well-appearing and thriving, unlike acute FPIES children. Present with blood streaked stools in first months of life.

Anaphylaxis: Time to symptoms is much shorter (usually minutes vs. 2-4 hours). Have constellation of associated symptoms not seen in FPIES: rash, respiratory distress/stridor. Symptoms resolve with IM epinephrine.

Infections/Sepsis: Usually present febrile (or less often hypothermic) and often with a history of sick contacts. Labs showing leukocytosis with a left shift/bandemia (vs eosinophilia in FPIES). There may be a presence of respiratory symptoms if sepsis 2/2 to PNA, viral URI. Septic patients typically do not improve with IVF alone (unlike FPIES patients).

Necrotizing enterocolitis: Systemic and abdominal symptoms seen in NEC that are not typical of FPIES include apnea, respiratory failure, temperature instability, intramural gas on abdominal radiograph. NEC is usually at a much earlier age, and often within the first few days of life.

Intestinal obstruction: There are reports of ex-laps being performed when acute FPIES was mistaken for ileus. Obstruction often presents with more pronounced distention and history of decreased to no stool output (FPIES infants can have normal stool output and/or diarrhea).

Intussusception: While the classic teaching is currant jelly stools, this is rarely present. Vomiting/discomfort waxing and waning over protracted period of time, and pain may be more predominant.

Pyloric Stenosis: Usually between 2 weeks and 2 months of life before the introduction of solid foods. There may be an olive-shaped mass in epigastrium, and ultrasound confirms the diagnosis.

Metabolic disorders: May have other features, such as hypoglycemia, hematologic abnormalities (ex, anemia, neutropenia, thrombocytopenia), liver dysfunction (hepatomegaly, jaundice), renal disease, and developmental delay.

Data shows that of FPIES patients presenting to the ED, 34% of patients undergoing abdominal imaging, 28% undergoing a septic evaluation, and 22% having a surgical consultation. Misdiagnosis and delays in diagnosis for children with food protein-induced enterocolitis syndrome were common, leading many children to undergo unnecessary investigations. (6, 7, 9)


The patient mentioned in the case earlier was subsequently admitted to the PICU for further workup and resuscitation. After many diagnoses were ruled out, and in conjunction with thorough dietary review, it was found that the patient had both of these episodes after exposure to sweet potato. The diagnoses of FPIES was made and patient was discharged to home in good health with rheumatology follow up.

For acute presentations, patients often require admission for fluid resuscitation, symptom management, and parent education. For chronic FPIES patients, it is sometimes reasonable to discharge patient to home, but this should always be done in conjunction with primary care doctor as well as expectant management and education. Often times, labs can be drawn in the emergency setting as a conduit to help the patient’s PCP rule out other causes (such as IgE-mediated allergies). (2, 3)

Faculty Reviewer: Dr. Jane Preotle



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  10. Figure A: Berin, M. Cecilia. Immunopathophysiology of food protein-induced enterocolitis syndrome. Journal of Allergy and Clinical Immunology, Volume 135. Issue5. 1108-1113