• Mouth breathing (Fig. 15.2a). Children who habitually breathe with their mouth open may have an obstructed nasal airway from rhinitis, and there may also be a history of snoring or obstructive sleep apnoea

Figure 15.2 Allergic facies. **(a)** There is a habitually open mouth due to mouth breathing. **(b)** An allergic salute, from rubbing an itchy nose. (Courtesy Dr George Du Toit.)

• An allergic salute (Fig. 15.2b), from rubbing an itchy nose

• Pale and swollen inferior nasal turbinates

• Hyperinflated chest or Harrison sulci from chronic undertreated asthma

• Atopic eczema affecting the limb flexures

• Allergic conjunctivitis; may also be prominent creases (Dennie-Morgan folds) and blue-grey discoloration below the lower eyelids.

Growth needs to be checked, especially in those with food allergy, where dietary restrictions or malabsorption can lead to nutritional compromise, and in those treated with high-dose inhaled/nasal/topical corticosteroids.

Management

The individual diseases are managed by general practitioners, general paediatricians or organ-specific specialists, e.g. eczema by dermatologists, asthma by respiratory paediatricians. However, allergic diseases coexist and it is therefore helpful to consider allergy as a systemic disease. The role of paediatric allergists is to identify triggers to avoid, and to manage children with multisystem or severe disease.

Management of specific conditions is described below. In addition, specific allergen immunotherapy can be used for treating allergic rhinitis and conjunctivitis, insect stings, anaphylaxis and asthma. During immunotherapy, solutions of an allergen to which the patient is allergic are injected subcutaneously or administered sublingually on a regular basis for 3–5 years, with the aim of developing immune tolerance. It is highly effective in providing protection for many years. However, it must be carried out under specialist supervision due to the risk of inducing severe allergic reactions (anaphylaxis). Allergen immunotherapy is widely used in the USA and some countries in Europe. Sublingual immunotherapy appears to be safer than subcutaneous injections and is used increasingly. Immunotherapy for food allergy is under investigation but has not yet been shown to be safe for use in clinical practice.

Summary

Paediatric allergy

• Includes food allergy, eczema, allergic rhinitis and conjunctivitis, asthma, urticaria, insect sting hypersensitivity and anaphylaxis

• Occurs when a genetically susceptible person reacts abnormally to an environmental antigen

• There is an ‘allergic march’ of disorders

• Different allergic diseases often coexist – if a child has one, look for others.

Food allergy and food intolerance

A food allergy occurs when a pathological immune response is mounted against a specific food protein. It is usually IgE mediated, but may be non-IgE mediated. A non-immunological hypersensitivity reaction to a specific food is called food intolerance. An example of each in relation to cow’s milk is shown in Figure 15.3.

Figure 15.3 Examples of food allergy and hypersensitivity to milk. **(a)** Clinical features of an acute allergic reaction. **(b,c)** Widespread urticaria and lip swelling after milk ingestion. (Courtesy Dr Pete Smith.)

Food allergy is usually primary, where children have failed to ever develop immune tolerance to the relevant food. Presentation varies with the agent and the child’s age:

• In infants, the most common causes are milk, egg and peanut

• In older children, peanut, tree nut and fish and shellfish.

Food allergy can also be secondary, where children initially tolerate a food and then later become allergic to it. Secondary food allergy is usually due to cross-reactivity between proteins present in fresh fruits/vegetables/nuts and those present in pollens, e.g. a child who can eat apples may develop allergy to apples in the future if they develop allergy to birch tree pollen, because the apple and birch pollen share a very similar protein. This is termed the ‘oral allergy syndrome’ or ‘pollen fruit syndrome’. It is very common but generally leads to milder allergic reactions than primary food allergy, often causing an itchy mouth but no systemic symptoms.

Non-IgE food allergy typically occurs hours after ingestion and usually involves the gastrointestinal tract.

Food allergy and intolerance are different from food aversion, where the person refuses the food for psychological or behavioural reasons.

Clinical features

In IgE-mediated food allergy there is a history of allergic symptoms varying from urticaria to facial swelling to anaphylaxis (Fig. 15.3), usually occurring 10–15 min after ingestion of a food. It is often the first occasion the food is knowingly ingested.

Non-IgE-mediated food allergy usually presents with diarrhoea, vomiting, abdominal pain and sometimes failure to thrive. Colic or eczema may also be present. It sometimes presents with blood in the stools in the first few weeks of life from proctitis.

Diagnosis

The most helpful screening tests for IgE-mediated food allergy are skin-prick tests (Fig. 15.4) and measurement of specific IgE antibodies in blood (RAST test). Both tests may yield false-positive results, but the greater the response, the more likely the child is to be allergic. Negative skin test results make IgE-mediated allergy unlikely.