Dr Suzanne Dowling Paediatric ST6, RLH General Paediatrics & Allergy

Reviewed by Dr A Aston Paediatric Allergy Consultant, RLH and Dr L Noimark Paediatric Allergy Consultant, RLH

Continuing from part one where we discussed how 6 year old Esther’s urticarial rash 10 hours after eating seeded bread does not fit with a food allergy, we will now explore other causes and what should happen next. 

What has caused this reaction?”

Esther’s mother is still very worried, she wants to know what has caused this reaction and if they can do anything to prevent it reoccurring. 

Common causes of acute urticaria +/- angioedema

Infections

  • Cause more than 80% of cases of urticarial rash in children (can be viral or bacterial). 
  • Childhood infective rashes are often misdiagnosed as urticaria.
  • Often the viral infection is mild or subclinical. 
  • Common pathogens include respiratory viruses and streptococcus.
  • Food allergies do not cause temperatures; think infection in a febrile child.

Autoimmune urticaria

  • Vasculitic urticaria can be painful, purplish and leave marks behind. 

(Other urticarias are itchy and don’t leave marks).

  • These need referral to specialist (e.g. rheumatology or dermatology).
  • It can be associated with other autoimmune conditions (e.g. SLE) so check for other indicative history/signs/symptoms (e.g. arthralgia, joint swelling, eye symptoms, etc.)

Medications (take a thorough drug history)

For example, NSAIDs can cause urticaria. 

While antibiotics (like penicillins) are often implicated in urticaria, 80% are misdiagnosed [6] and are likely due to the infection they are given to treat.

ACE Inhibitors are known to cause angioedema. [4] 

Physical or inducible urticarias

  • Triggers include – pressure/dermatographia (including a delayed pressure effect), heat / cold, exercise, stress, water (this is not a water allergy). 
  • Symptoms tends to be short lasting (around 30 minutes to 1 hour). 
  • Management involves avoiding triggers.

Idiopathic

  • In many cases there is no identifiable cause.

ALSO: 

Chronic Urticaria

  • Defined as urticaria that occurs on most days for 6 weeks or more. [3]
  • Management is symptom control with daily/as needed antihistamine.
  • These patients may need more than the regular doses of antihistamine (there are national guidelines [7] around management in Primary and Secondary care).
  • These patients can be referred to/discussed with an allergist if there is a diagnostic uncertainty or failure of treatment.

Anything else to consider? 

Hereditary angioedema is a rare form of angioedema which runs in families. These patients do not have associated wheals. Patients get swelling of face, mouth, throat and sometimes gut. These patients have a problem with the complement pathway, which requires specific investigation.


Differentiating Urticaria from Urticarial Rashes:

There are a large number of medical conditions (including food allergies) and infections that can cause urticaria or an urticaria-like (urticarial) rash. Differentiating what is happening in your patient (using the table below) will help you narrow down the list of potential causes.

Back to Esther

Esther was feeling well in herself with no clear symptoms of an infection (although these can take time to appear).  She has not taken any medications and there didn’t appear to be a trigger such as heat, cold or pressure.  This is most likely a case of idiopathic urticaria, however, there is no diagnostic test for this.

You can reassure the parents that this is not an allergic reaction to a food and provide some treatment with antihistamines.  

Urticaria +/- angioedema symptoms can wax and wane over several days, even with treatment and you should warn the parents about this. 

You should also safety net, as additional symptoms may appear over time (e.g. pyrexia in infection or autoimmune conditions). They should feel comfortable seeking a further medical review, if she is deteriorating. 

Can we do any tests Doctor?’

Investigations are usually unhelpful in acute urticaria.  If the history is not in keeping with allergy, only around 1% of children will have any positive findings with blood tests.  Unless there are concerning features there is no need to investigate/refer an isolated episode of urticaria/angioedema.  Food allergy testing would only be indicated if the history is in keeping with a food allergy, as per the EATERS history above. 

Top Tips: Allergy Tests

Positive skin prick tests and specific IgE blood tests indicate the presence of specific IgE antibodies. This confirms the patient is sensitised to the allergen but not necessarily allergic.

To diagnose an allergy, the patient must have a consistent history of reaction to that allergen (e.g. peanut) AND a positive test.

If a person is consuming a food on a regular basis with no acute reaction, the result of the test is meaningless, as the patient is tolerant. Remember it is possible to get false positive allergy tests. This is why we don’t advise a ‘fishing expedition’, for potential allergenic triggers, as these can lead to unnecessary food restriction.

Treatment

The aim of urticaria treatment is to achieve symptom control.  First line treatments are oral antihistamines such as chlorphenamine maleate or Cetirizine (we recommend using the non-sedating ones as they also have a longer duration of action).

Steroids are part of the national guidelines for acute recurrent cases [7] but are not standard treatment for all patients and are not for regular use. 

If the urticaria appears chronic (lasting for more than 6 weeks) discuss with the family/patient about starting a daily antihistamine.  Doses can be increased for any breakthrough symptoms and may exceed the standard treatment in the BNFc, hence use the national guidelines. [7] 

Who needs referring to specialist?

If you think it may be an allergic reaction, refer to an allergist.  

In chronic urticaria, if there is diagnostic uncertainty or failure of treatment then consider discussion with/referral to an allergist.

In suspected vasculitic /autoimmune urticaria refer to an allergist, dermatologist, immunologist or rheumatologist.

If you suspect Hereditary angioedema – refer to an immunologist.

Key Points

  • Urticaria is very common.
  • It is uncommon for it to be due to an allergy, without a clear history.
  • Remember the ABC assessment in acute presentations. 
  • Take an EATERS history as part of your assessment of an allergic cause.
  • Infections are a common cause in children.
  • Investigations are usually unhelpful.
  • Always get family to take a photograph of rash/swelling (if face-to-face do it yourself using the family phone, for the best image).
  • Single isolated episodes of urticaria and angioedema do not need specialist referral.

References

  1. Methods report on the development of the 2013 revision and update of the EAACI /GA2LEN /EDF /WAO guideline for the definition, classification, diagnosis, and management of urticaria
  2. Allergy UK: Urticaria, hives and other skin allergy
  3. BSACI guideline for the management of chronic urticaria and angioedema
  4. BMJ Best Practise Urticaria and angio-oedema [Updated 2018]
  5. Fifteen-minute consultation: The EATERS method for the diagnosis of food allergies Archives of Disease in Childhood – Education and Practice 
  6. Perioperative AnaphylaxisAnaesthesia, Surgery and Life-Threatening Allergic Reactions 
  7. BSACI guideline for the management of chronic urticaria and angioedema

 

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