Clinical presentation
Peanut and tree nuts are among the most commonly implicated foods in cases of anaphylaxis occurring in both children and adults.11,12 Anaphylaxis has been defined as an acute, life-threatening allergic reaction, involving more than one organ system in the body.13 The pathophysiology of anaphylaxis involves release of mediators from mast cells and basophils upon allergen exposure, such as after ingestion of peanut or tree nuts.9 The release of mediators such as histamine, leukotrienes, and prostaglandins result in pathophysiologic events including smooth muscle contraction, increased vascular permeability, vasodilation, and stimulation of the nervous system with reflex vagal activation.14 These physiologic effects result in the classic symptoms of anaphylaxis, which include cutaneous and mucosal involvement in the form of urticaria and angioedema; respiratory symptoms such as cough, wheezing, or dyspnea; abdominal symptoms including vomiting, diarrhea, and uterine contractions; as well as hypotension; and in severe cases, hypovolemic shock. Gastrointestinal symptoms are more commonly observed in cases of food-induced anaphylaxis compared with anaphylaxis from other causes.15 Features of anaphylaxis differ based upon age of the patient.16 Cardiovascular collapse is reported more often in adults, compared with hives, vomiting, wheezing, and stridor in children.17,18 Anaphylaxis in infants is more likely to be underdiagnosed due to atypical clinical presentations with nonspecific symptoms such as lethargy and irritability, as well as inability to subjectively report symptoms.19
In the case of nut-induced anaphylaxis, as with other foods, symptoms typically present within 5–30 minutes of ingestion.20 Biphasic reactions, in which return of anaphylactic symptoms occurs following an asymptomatic period of an hour or more after the initial reaction, without further exposure to antigen, can occur in 3%–20% of severe food reactions.9,21,22 However, the mechanism of biphasic anaphylaxis is largely unknown, and these late phase reactions have been observed in only 2% of anaphylaxis induced by foods during inpatient oral food challenges (OFCs).23 Biphasic reactions typically develop within 8 hours of resolution of the initial reaction, but may occur up to 72 hours later.24 Risk factors for late phase reactions may include delayed onset of initial symptoms (>30 minutes), β-blockade, administration delay or inadequate dose of epinephrine, as well as reaction to an ingested allergen (food), as opposed to an injected allergen.22
Foods are the most common cause of anaphylaxis in the outpatient setting, representing up to half of all cases of anaphylaxis treated in emergency departments in the USA.25 Additionally, food triggers account for up to 50%–80% of anaphylactic reactions in children.9,11 Perhaps even more importantly, food allergens account for 30% of fatal cases of anaphylaxis with an estimated 100 deaths per year due to food-induced anaphylactic reactions.26,27 Risk factors for fatal food anaphylaxis include an allergy to peanuts or tree nuts, a history of asthma, and failure to administer epinephrine promptly.28 Adults are up to nine times more likely to develop severe peanut or tree-nut-allergic reactions than children.28 Adolescents and young adults are also at risk for life-threatening anaphylaxis, given risk-taking behavior and frequent underreporting of symptoms in these age groups.