After reading this chapter you should be able to:
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to assess, diagnose and manage allergies
Allergic conditions can present in a wide variety of ways from mild episodic rashes through to dramatic, rapid-onset, life-threatening illness. Many symptoms are common to those seen in other conditions and consequently the true aetiology can be missed and inappropriate diagnoses and management plans provided. Similarly, an incorrect allocation of an allergic cause to some of the problems presented in children can impact on their lifestyle. Although many atopic conditions can be managed by the general paediatric team, those with multisystem atopy, IgE food allergy or drug allergy require the advice and input of colleagues in a specialist allergy service.
Allergic reactions and anaphylaxis
Every year many children attend for unscheduled care at their primary care centre or local emergency department due to acute symptoms suggestive of allergy. The responses will vary from mild rhinitis or conjunctivitis or cardiorespiratory collapse due to an anaphylactic reaction.
Clinical presentation
Features of an allergic reaction include:
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urticaria
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peri-orbital oedema
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oral mucosal irritation
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vomiting
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diarrhoea
The child with acute anaphylaxis will have stridor due to laryngeal oedema, respiratory distress with wheeze or acute circulatory collapse. Children or young people presenting in this way require urgent action.
Treatment and management
The immediate response to a child with acute anaphylaxis is the administration of intramuscular adrenaline. This administration must not be delayed whilst attempting to secure intravenous access or other hierarchical manoeuvres on the ABC pathway. A second dose of IM adrenaline can be given after 5 minutes if the patient has shown little or no evidence of clinical improvement. The airway should be maintained, supplemental oxygen given and intravenous crystalloid fluids provided in the knowledge that the adrenaline is administered. Any potential colloids which might be causative to anaphylaxis should be stopped. Chlorpheniramine and hydrocortisone should also be administered either IM or as a very slow IV dose. The anaphylaxis algorithm 2021 produced by the Resuscitation Council (UK) summarises the management plan ( Figure 14.1 ).
Investigations
There are no investigations required during an episode of acute anaphylaxis although a blood sample taken after the child is stable may reveal an elevated tryptase (produced by mast cells) level. This would indicate that the presenting problem was due to an allergic reaction rather than any other cause of the acute collapse. If the history implicates a potential allergen, then a specific IgE can be requested.
Relevant pharmacological agents used
Nonsedative antihistamines should be used in the acute situation to ensure that sedation does not confuse the acute management. Similarly, when prescribed as part of a take home allergy plan, nonsedating antihistamines, such as cetirizine, are most commonly used due to their duration of action.
Adrenaline will relieve bronchospasm and support central blood pressure by vasoconstriction and therefore requires prompt administration. Adrenaline autoinjectors allow patients and carers to administer doses quickly and easily if necessary and are produced in two dose strengths—150 mcg and 300 mcg. It is important to explain the correct administration technique to the patient and family ( Table 14.1 ).
| Dose | Age |
|---|---|
| Under 6 years | 150 micrograms |
| 6 to 12 years | 300 micrograms |
| Over 12 years | 500 micrograms |
Important sequelae
After the episode of the allergic reaction has been managed, it is important that a plan is put in place to ensure the child or young person remains safe in the future. A period of observation may be necessary, particularly if anaphylaxis was the presenting problem, and the current NICE guidelines advises a 12-hour period for those under 16 years. Clearly an attempt must be made at identifying the trigger so that appropriate avoidance advice can be given and an ‘allergy plan’ put in place. Templates for such plans are available online. The details of the reaction must be recorded in GP and hospital notes and a medical alert added to electronic records. A referral to a clinician with expertise in allergy management should be made if there is a concern regarding IgE-mediated food allergy, drug allergy or acute bronchospasm secondary to aeroallergen exposure.
Food allergy
Food allergy is common and affects up to 8% of infants in the UK. Many of the symptoms are nonspecific, leading to the diagnosis being overlooked or dismissed. There is, however, an increasing number of children being wrongly diagnosed with food allergy, probably due to a greater public awareness of allergies. The most important diagnostic tool for food allergy is a focused clinical history which enquires about:
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family and personal history of atopy
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relevant signs and symptoms
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how signs and symptoms related to the food ingested in terms of onset
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details of previous management of the condition
It will also consider the need for, and interpretation of, any investigations.
In general, non-IgE mediated food allergies carry a more favourable prognosis with resolution common and likely to occur before 3–5 years of age in most children. In those with IgE-mediated food allergy, the prognosis differs depending on the allergenic food ( Table 14.2 ). The majority of children with milk and egg allergy will experience full resolution over time whilst those with nut, fish and seafood allergies usually have lifelong problems.
| IgE-mediated food allergies | Nonallergic (non-IgE) food hypersensitivity | |
|---|---|---|
| Typical signs and symptoms | urticarial rash; itchy red skin; swollen lips and eyes; itchy mouth and throat; vomiting; anaphylaxis | gastroesophageal reflux; vomiting; diarrhoea or constipation; blood or mucous in stools; eczema; poor weight gain |
| Onset of symptoms in relation to food ingestion | within minutes (up to 1 hour) | several hours or days (usually 4–72 hours) |
| Duration of symptoms following onset | few hours | several days |
| Frequency of symptoms | Episodic but each time the food ingested | chronic (since usually caused by a food consumed very frequently) |
| Common foods leading to allergy | egg milk peanuts other common foods: soya, tree nuts, sesame, fish, shellfish, wheat | milk soya wheat |
| Age of onset | 1–4 years but can develop later | within the first year |
There is a distinction in management between allergic reactions and nonallergic hypersensitivity reactions to food as demonstrated by the difference between cow’s milk protein allergy and lactose intolerance. There is also a difference between IgE and non-IgE mediated food allergy in diagnosis, management and prognosis.
Contrary to earlier beliefs, it is now known that a prior episode of ingestion is not required in order to develop allergic sensitisation. Defective skin and gut barriers combined with altered microbiome (caused by caesarean birth, inappropriate use of antibiotics, antacids) are thought to play a big role in food allergy pathogenesis, alongside genetic factors such as a family history of atopy.
Clinical presentation
Children with adverse reactions to food can present with a wide and varied range of symptoms including:
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cutaneous rashes
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eczema
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vomiting
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diarrhoea
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poor weight gain
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mucosal sensitivity
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acute anaphylaxis
Investigations
Supportive allergy investigations are available for the confirmation or exclusion of IgE-mediated food allergy, including skin prick tests, specific IgE tests and oral food challenge tests. These tests are not appropriate for the investigation of non-IgE mediated food allergy, where the only investigative tool is exclusion diet followed by reintroduction to prove causality between suspect food and clinical symptoms.
Skin prick testing or specific IgE testing should be directed at suspected trigger foods and not for foods which the patient is consuming on regular basis without consistent symptoms after each and every ingestion.
Interpretation of a positive skin prick test ( Figure 14.2 ) or specific IgE test must be undertaken with caution in children with coexisting atopic disease such as eczema, asthma, allergic rhinoconjunctivitis and eosinophilic gut
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explain procedure to child and carers
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ensure no antihistamines in last 72 hours (ideally 5 days)
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ensure medications and equipment to treat allergic reaction available
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use volar aspect of the forearm and ensure skin appears normal
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mark skin with the initial letter of the allergen being tested
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mark skin for controls—POS + (histamine) and NEG—(normal saline)
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apply drop of extract and push lancet gently through drop
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use separate lancet for each drop
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read at 15 minutes after positive completed
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measure the longest extent of the wheal (excluding the flare) in millimetres
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wheal diameter of 3 mm or larger is considered positive
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IgE-mediated allergy to the test allergen is more likely with large wheal
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size of wheal cannot not predict severity of future allergic reactions
A 7-month-old infant with severe early-onset eczema was being fed by her mother. During the meal the infant developed perioral urticaria which quickly progressed to generalised urticaria, lip swelling, coughing and breathing difficulties. The infant then went limp and floppy and her mother called an ambulance. The meal consisted of a homemade puree of chicken and vegetables made with a stock cube. The infant previously tolerated this same meal the week before. On arrival at hospital, the infant was resuscitated with adrenaline, had intravenous fluids and antihistamines and was observed overnight. Her parents were told not to give her the meal again or any of the constituents and to carry their adrenaline auto-injectors and antihistamines at all times. Appropriate training and management plans were given prior to discharge and bloods taken for specific IgEs to chicken, carrot, onion and celery.
The infant was seen in clinic 2 weeks later and her eczema remained florid. Her specific IgEs to chicken, carrot, onion and celery were all negative and prick-to-prick testing to the puree was also negative. Further history taking revealed that her mother had been eating scrambled egg whilst feeding the infant and had cross-contaminated the puree when checking to ensure the puree was of the correct temperature. The infant had a 12 mm wheal to egg.
Common allergens in infancy are egg, dairy, wheat, nuts, sesame, fish and soya, and it is important to take a detailed allergen-focused history in any child with a history of anaphylaxis asking about potential exposure to these major allergens in particular. Anaphylaxis to trace exposure is uncommon but it is essential that the allergen responsible is identified as soon as possible and appropriate avoidance advice given.
