A number of specific clinical syndromes may occur as a result of FA and their definitions are as follows:
1. Food-induced anaphylaxis is an IgE-mediated, rapid-onset, potentially life-threatening systemic reaction, in which an affected individual may experience cardiovascular shock and/or serious respiratory compromise due to airway obstruction or bronchoconstriction.
2. Gastrointestinal food allergies include a spectrum of disorders that results from the adverse immunologic responses to dietary antigens. Although there may be significant overlap between these conditions, several specific syndromes have been described.
These are defined as follows:
- Immediate gastrointestinal hypersensitivity refers to an IgE-mediated FA in which upper gastrointestinal (GI) symptoms may occur within minutes and lower GI symptoms may occur either immediately or with a delay of up to several hours. This is commonly seen as a manifestation of anaphylaxis.
Among the GI conditions, acute immediate vomiting is the most common reaction and perhaps the one best documented as immunologic and IgE Mediated.
- Eosinophilic esophagitis (EoE) involves the localized eosinophilic inflammation of the esophagus. While EoE is commonly associated with the presence of food-specific IgE, the precise causal role of FA in its etiology is not well defined. Both IgE- and non-IgE-mediated mechanisms seem to be involved based on the facts that food avoidance frequently leads to resolution, and that the responsible foods cannot always be identified by IgE testing. In children, EoE is responsible for feeding disorders, vomiting, hypersensitivity reflux symptoms, and abdominal pain. In adolescents and adults, it is most often present with dysphagia and esophageal food impactions.
- Eosinophilic gastroenteritis (EG) also is both IgE- and non-IgE-mediated, and commonly linked to food allergies. EG describes a constellation of symptoms that vary depending on the portion of the GI tract involved and a pathologic infiltration of the GI tract by eosinophils that may be quite localized or very widespread.
- Dietary protein-induced proctitis/proctocolitis is typically present in infants who seem generally healthy but have visible specks or streaks of blood mixed with mucus in the stool. IgE to specific foods is generally absent. The lack of systemic symptoms, vomiting, diarrhea, and growth failure help to differentiate this disorder from other gastrointestinal food allergies that present with similar stool patterns. Because, there are no specific diagnostic laboratory tests, the causal role of food allergens such as those found in cow’s milk or soy are inferred from a characteristic history on exposure. Many infants present while being breastfed, presumably as a result of maternally- ingested proteins excreted in breast milk.
- Food protein-induced enterocolitis syndrome (FPIES) is another non-IgE-mediated disorder presenting in infancy with vomiting and diarrhea severe enough to cause dehydration and shock. Cow’s milk and soy protein are the most common causes, although some studies also report reactions to other foods, including rice, oat, or other cereal grains. A similar condition has also been reported in adults, most often related to crustacean shellfish ingestion.
- Oral allergy syndrome (OAS), also referred to as pollen-associated FA syndrome, is a form of localized IgE-mediated allergy, usually to fresh fruits or vegetables, confined to the lips, mouth, and throat. OAS most commonly affects the patients who are allergic to pollens. Symptoms include itching of the lips, tongue, roof of the mouth, and throat, with or without swelling, and/or tingling of the lips, tongue, roof of the mouth, and throat.
3. Cutaneous reactions to foods are some of the most common presentations of FA and include IgE-mediated (urticaria, angioedema, flushing, pruritus), cell- mediated (contact dermatitis, dermatitis herpetiformis), and mixed IgE- and cell- mediated (atopic dermatitis) reactions. These are defined as follows: Acute urticaria is a common manifestation of IgE-mediated FA, although FA is not the most common cause of acute urticaria and is rarely a cause of chronic urticaria. Lesions develop rapidly after ingesting the problem food and appear as polymorphic, round or irregularly shaped pruritic wheals, ranging in size from a few millimeters to several centimeters.
- Angioedema most often occurs in combination with urticaria and, if food induced, is typically IgE mediated. It is characterized by nonpitting, nonpruritic, well-defined edematous swelling that involves subcutaneous tissues (e.g., face, hands, buttocks, and genitals), abdominal organs, or the upper airway (i.e., larynx). Laryngeal angioedema is a medical emergency requiring prompt assessment. Both acute angioedema and urticaria are common features of anaphylaxis.
- Atopic dermatitis/atopic eczema (AD) is linked to a complex interaction between skin barrier dysfunction and environmental factors such as irritants, microbes, and allergens. Null mutations of the skin barrier protein filaggrin may increase the risk for transcutaneous allergen sensitization and to the development of FA in subjects with AD. The role of food allergy in the pathogenesis of these conditions remains controversial. In some sensitized patients, particularly infants and young children, food allergens can induce urticarial lesions, itching, and eczematous flares, all of which may aggravate AD.
- Allergic contact dermatitis is a form of eczema caused by cell-mediated allergic reactions to chemical haptens present in some foods, either naturally (e.g., mango) or as additives. Clinical features include marked pruritus, erythema, papules, vesicles, and edema.
- Contact urticaria can be either immunologic (IgE-mediated reactions to proteins) or non-immunologic (caused by direct histamine release).
4. Respiratory manifestations of IgE-mediated FA are important components of anaphylaxis but are uncommon in isolation. This is true for both upper (rhinitis) and lower (asthma) respiratory symptoms.
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