A GP guide to urticaria in children
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Need to know:
- Acute urticaria is common in children and more often associated with acute infection than immunoglobulin E (IgE)-mediated allergy.
- Chronic urticaria is less common in children than adults; among children, adolescents are more commonly affected.
- The majority of cases of chronic urticaria in children are ‘spontaneous’, that is, there is no clear underlying cause, although an autoimmune basis is likely in many cases.
- Treatment of urticaria is with regular non-sedating oral antihistamine, often in higher doses than usually prescribed; oral steroids should be reserved for children with acute urticaria not responding to high-dose antihistamine.
- Referral to an allergy specialist is warranted in children with urticaria suspected to be a result of an IgE-mediated allergy, chronic urticaria (greater than six weeks), an inducible urticaria or if atypical red flags are present.
Urticaria is a condition characterised by the presence of wheals, angioedema, or both.
Urticarial lesions, also commonly known as wheals, hives or welts, are lesions with a sharply circumscribed superficial central swelling of variable size and shape, with or without surrounding erythema.
Lesions are usually intensely itchy, and are transient in nature, lasting for 30 minutes up to 24 hours.
Angioedema is deeper swelling within the lower dermis or mucous membranes, and can produce a tingling, burning, itching or sometimes painful sensation, and generally lasts longer than a typical urticarial lesion (up to 72 hours before resolution).1
Urticaria results from release of histamine and other vasoactive mediators from mast cells and basophils in the superficial dermis, resulting in extravasation of fluid into the dermis and the typical urticarial lesion. The same process occurring deeper in the dermis and subcutaneous tissues gives rise to angioedema.2
Urticaria can be classified into types based on its chronicity (acute or chronic) and/or whether there is an identifiable cause (spontaneous or inducible).
Acute urticaria is defined as urticaria present for less than six weeks, whereas chronic urticaria is defined as persistent hives present on most days of the week and lasting six weeks or more. Chronic urticaria is most commonly spontaneous (idiopathic) in nature.
Prevalence
Urticaria is common, with a lifetime prevalence of 20%.3 Acute urticaria is more common in children, and most infants and children presenting with urticaria will have the acute form.
Less than 10% of children will go on to develop chronic urticaria, which is usually seen in adolescents and older children. Recurrent acute urticaria is seen in 10-30% of young children.3
Subtypes and causes
Acute urticaria
Infections are a common causes of acute urticaria in children. Infections are associated with over 80% of acute urticaria presentations in children in some paediatric case series.4
The implicated organisms are varied and include common viral illnesses (such as respiratory syncytial virus, Herpesviradae infections, picornavirus, coronavirus), bacterial infections (eg, UTIs, Mycoplasma pneumoniae) and gastrointestinal parasites.5,6
Urticaria can appear during the course of the illness, or soon after the illness has resolved. The child otherwise appears well, and urticaria usually lasts for a few days.
Immunoglobulin E (IgE)-mediated allergic reactions are another common cause of acute urticaria in childhood. These include reactions to foods, medications or stinging insects. Usually, a trigger is identified as having been ingested (or in the case of venom allergy, a sting) just prior to the onset of urticaria (within minutes to two hours of exposure).
Other associated symptoms to suggest an IgE-mediated allergic reaction include vomiting, abdominal pain, throat tingling, cough, wheeze or other breathing difficulties, and cardiovascular compromise.
Prompt resolution of symptoms (within hours of onset) and the reproducible nature of this condition (that is, symptoms occur after every exposure), are other key pointers to the diagnosis.
Idiopathic acute urticaria, when a specific cause is not identified, is another common diagnosis in cases of acute urticaria in children.
Less common causes of acute urticaria in children include NSAIDs. The mechanism in these cases is either via a pseudoallergic/pharmacological mechanism (due to inhibition of the COX-1 enzyme) or true IgE-mediated drug allergy (more commonly the former).
Direct mast cell activation is another uncommon cause of acute urticaria in children. In this condition, certain medications cause mast cell degranulation resulting in urticaria through a non-IgE-mediated process. Examples include opioids (codeine, morphine) and dextromethorphan (a cough suppressant found in many over-the-counter cold and flu medications).
Chronic urticaria
This presentation in children is far less common than acute urticaria, with reported prevalence rates of 0.1% to 3%. Among children, chronic urticaria is more commonly seen in adolescents and older children, and the vast majority of these cases are spontaneous in nature (termed, ‘chronic spontaneous urticaria’).7
Chronic spontaneous urticaria
The exact pathogenesis of chronic spontaneous urticaria is not yet fully understood, but an autoimmune basis for this condition is likely in many cases, with both type I (IgE autoantibodies to self-antigens) and type II (mast cell-directed activating autoantibodies) autoimmunity being implicated, as well as other as yet unknown mechanisms.8
While other autoimmune conditions, particularly thyroid autoimmune disease, is strongly associated with chronic spontaneous urticaria in adults, this is less commonly seen in children. Aggravating factors such as the use of NSAIDs, stress and excessive heat have been identified as important in influencing disease severity and activity in patients with chronic spontaneous urticaria.
The prognosis is good in that it is a self-limiting condition; however, resolution in children can be slow (~10% resolution rate per year, although reported resolution rates vary significantly which likely reflects the small numbers studied).
Inducible urticaria
Inducible urticaria is considered a subtype of chronic urticaria. In some patients, a physical stimulus is the only trigger for urticaria, but in others there can be both an identifiable physical stimulus as well as urticaria occurring spontaneously.
The exact pathogenesis is not known but it is likely a result of heightened sensitivity of mast cells to environmental conditions.9 Subtypes of inducible urticarias in children are outlined in box 1.10
| Box 1. Subtypes of inducible urticaria in children |
| • Dermatographism — urticaria resulting from firm stroking or scratching of the skin • Cold urticaria — resulting from exposure of skin to cold air/liquids/objects • Cholinergic urticaria — resulting from elevation of core body temperature (eg, during exercise, consuming hot beverages, hot/spicy food) • Aquagenic — resulting from skin contact with water • Delayed pressure urticaria — urticaria appears in areas where pressure was applied up to 12 hours prior (such as waistbands, crop tops, tight clothing) • Heat urticaria — resulting from skin contact with a warm object • Exercise induced urticaria/anaphylaxis — in association with physical exertion • Solar urticaria — resulting from direct exposure to the sun |
Treatment
Non-pharmacological measures include avoidance of triggers (if known) and aggravating factors such as heat, NSAIDs and stress. Cool compresses or a cool bath/shower can help alleviate associated itch.
Pharmacological
Second-generation H1-antihistamines (such as cetirizine, loratadine, desloratadine and fexofenadine) are the mainstay of treatment in both acute and chronic urticaria in children and adults. They are safe and usually very effective at controlling urticaria.
For acute urticaria, treatment is with once or twice daily dosing of antihistamine (such as cetirizine 0.5mg/kg daily or 0.25mg/kg twice a day), until resolution of urticaria (usually only required for a few days to weeks).11 A single dose of oral prednisolone (0.5-1mg/kg, max 60mg) can be considered in severe cases of acute urticaria not responding to antihistamines.
For chronic urticaria, treatment is initially the same as acute urticaria, but the dose of antihistamine can be increased to up to four times the recommended daily dose (eg, cetirizine 1mg/kg/day up to a maximum of 40mg/day).
Omalizumab is a recombinant humanised monoclonal anti-IgE antibody, which is safe and effective for treatment of chronic spontaneous urticaria in patients aged seven and older. This is generally the next line treatment for patients with persistent symptoms despite regular high-dose antihistamine.12
Omalizumab is available on the PBS via an authority prescription from an allergist, immunologist or dermatologist. Common side effects include headache, fatigue and injection site reactions.
The risk of anaphylaxis is low but not negligible (0.2% reported rate, with most episodes occurring within the first three doses).12 For this reason patients usually receive the first three doses in a hospital or specialist clinic familiar with management of anaphylaxis. Patients are also co-prescribed an adrenaline autoinjector and should carry this for the 24 hours following omalizumab administration.
Red flags
Urticarial lesions that are long lasting (greater than 24-48 hours), painful, or leave residual bruising suggest urticarial vasculitis. These warrant a different approach to workup and management.
Angioedema without urticaria suggests other angioedema disorders, such as idiopathic angioedema, and hereditary and acquired C1 inhibitor deficiency.
Systemic features such as fever, arthralgias and conjunctivitis along with recurrent urticaria suggest a cryopyrin-associated periodic syndrome.
Flushing, tachycardia and gastrointestinal symptoms (nausea, vomiting, diarrhoea) along with a rash that is similar in appearance to urticaria suggest a mast cell disorder (such as urticaria pigmentosa or systemic mastocytosis).4
When to refer
Allergist referral is warranted for any suspected IgE-mediated food, medication or stinging insect allergy. Additionally, cases with a suspected infectious cause, but with contemporaneous use of an antibiotic or other medication during the infectious illness, warrant referral to assess and rule in/out medication allergy.
Urticaria lasting more than six weeks and suspected inducible urticaria require allergist involvement. Allergist and/or other relevant specialist involvement (such as a dermatologist) is recommended if any red flag signs or symptoms are present.
Conclusion
Acute urticaria is a common condition of childhood, and in the majority of cases an acute infectious agent is the culprit.
This can typically be managed symptomatically, with appropriate home-based non-pharmacological and pharmacological measures. However, allergist input is warranted when there is a suspected IgE-mediated food, medication or insect allergy, urticaria lasting for more than six weeks, or presence of any red flag features.
Earn CPD hours: How to Treat — Urticaria in adults
Dr Gabrielle Mahoney is a paediatric allergist and immunologist at the Royal Children’s Hospital, Melbourne Allergy Centre and Children’s Specialists, and Epworth Allergy Specialists, Melbourne, Victoria.
