IV. Food Allergy

A.Definition. Food allergy is an IgE-mediated response to food antigens.

B.Etiology. Most allergic reactions to food (85–90%) are caused by egg, milk, peanut, tree nuts, soy, wheat, and fish.

C.Clinical features

1.Skin involvement such as acute urticaria and angioedema (approximately 90% of reactions)

2.Oral symptoms such as itching and swelling of the lips, tongue, or throat

3.Gastrointestinal (GI) symptoms such as nausea, vomiting, diarrhea, and abdominal pain

4.Respiratory symptoms such as nasal congestion, rhinorrhea, sneezing, and wheezing

5.Key point: When these symptoms involve two or more organ systems (i.e., skin and GI tract), the reaction is called anaphylaxis.

D.Diagnosis

1.History should elicit the types of symptoms, the timing of symptoms in relation to food ingestion, and the reproducibility and severity of symptoms. Histories are often not specific, and there may be confusion between a true immediate allergic reaction (IgEmediated) and a late reaction to a food (non-IgE mediated).

2.Laboratory evaluation

a.Skin tests may be helpful in identifying foods responsible for IgE-mediated hypersensitivity reactions.

b.RAST tests identify serum IgE antibodies to specific food antigens.

3.Provocative oral food challenge is necessary to determine whether a patient has true food hypersensitivity. Double-blind placebo-controlled food challenge is the gold standard.

E.Management

1.Strict avoidance of the responsible food allergen is the best therapy.

2.Injectable epinephrine should be carried by food-allergic patients who have a history of severe reactions to foods.

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V.Insect Venom Allergy

A.Definition. Insect venom allergy is an IgE-mediated response to the venom of stinging or biting insects.

B.Etiology. The venom of many insects, including yellow jackets, hornets, wasps, bees, and fire ants, may cause allergic reactions.

C.Clinical features range from localized erythema and swelling to urticaria and to anaphylaxis.

D.Management

1.Local skin reactions can be treated with cold compresses, analgesics, and antihistamines.

2.Diffuse urticaria can be treated with antihistamines, but may require treatment with systemic cortico steroids.

3.Anaphylaxis can be treated as described in section I.E.

4.Immunotherapy is effective.

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VI. Urticaria (Hives)

A.Definition. Urticaria is circumscribed, raised, evanescent (vanishing) areas of edema and erythema that are almost always pruritic. Hives are usually symmetric and migratory.

B.Etiology. The causes of urticaria are extensive, and some are listed in Table 15-2.

C.Classification. There are two types of urticaria.

1.Acute urticaria is often precipitated by exercise, heat, cold, pressure, occupational exposure, medications, insect bites, foods, or recent infections. Health care workers and patients with myelomeningocele (who are commonly exposed to latex because of the need for repeated urinary catheterization) are at risk for latex allergy, which can present as urticaria.

2.Chronic urticaria (urticaria that lasts >6 weeks) may be associated with underlying conditions such as malignancy and rheumatologic diseases. A substantial proportion of patients with chronic urticaria have an IgG antibody to the IgE receptor.

D.Management. The precipitating factor should be avoided, if it can be identified.

1.Antihistamines are the mainstays of therapy.

2.Further evaluation for underlying systemic disease is indicated in patients with chronic urticaria, especially if the urticaria is associated with other symptoms such as fever, arthralgias, weight loss, or abdominal pain.

Table 15-2

Causes of Urticaria

1. Nuts

Contactants

1. Animal dander

1. Latex

Idiopathic

Infection

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1. Group A β-hemolytic streptococcal pharyngitis

1. Infectious mononucleosis

1. Mycoplasma pneumoniae

1. Hepatitis

1. Coxsackievirus

Insect venoms

Transfusion reaction

Heat and cold

Skin pressure

Exercise

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