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Urticaria

John Kelso, MD, Ilene Claudius, MD, and Solomon Behar, MD
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Ilene, Sol and John discuss the presentation of urticaria, differential diagnosis and indications for allergy referral.

 

Pearls:

  • One of the most distinguishing features of an urticarial rash is that it is pruritic and fleeting, coming in going in different parts of the body.

  • First line treatment for urticaria is a non-sedating H1 blocker at the normal daily dose; if this is not sufficient in suppressing the urticaria, this same medication should be uptitrated to BID, TID or QID dosing.  

  • bPrescribe  an autoinjectable epinephrine device when a suspected  immediate (IgE mediated) allergic  food, medication or insect sting/bite urticaria trigger has been identified

 
  • What do urticarial lesions look like? These lesions are red, raised, pruritic and fleeting, often not lasting for more than a few hours or a day and coming and going on different parts of the body.

  • What causes an urticarial reaction? An urticarial lesion involves mast cell degranulation.  Mast cells release histamine. Many families believe that if their child has hives (urticaria), it must be an allergy; however, most hives are not caused by a true allergy.

    • If there is an allergic trigger to the urticaria, the temporal association between exposure to the allergen and the onset of the rash is closely correlated within minutes. These IgE mediated allergic reactions are immediate type hypersensitivity reactions in which the allergen has to gain access to the blood stream, as is the case with food or medicine.

      • Rare examples of “contact urticaria” exist in which touching an allergen to the skin causes hives; however, for this, the skin needs to be wet or broken.  Contact dermatitis can certainly occur with a chemical substance touching the skin. While the rash is raised and pruritic, it is not fleeting. The exposure may have happened days before.

        • Having a chemical substance, for example from a perfume or lotion, come in contact with dry, intact skin cannot make you break out in hives because there aren’t mast cells on the skin.

          • In a patient who has a latex allergy and puts on latex gloves, the urticaria this patient gets would be due to the sweating under the gloves and the allergen getting a chance to soak through the skin to affect the mast cells.

      • If the hives are related to food and/or medicine, the child would need to have some prior exposure to develop the IgE antibodies in the first place and perhaps more importantly to elicit  on history, is the timing of eating and/or medication administration and the appearance of hives.

  • Are there typical infections that are associated with the development of hives?  Literature suggests that viral infections, like EBV, are more likely to cause hives than bacterial infections.  Note that many viral infections can cause hives.

  • What is the mechanism for chronic urticaria and/or urticaria without an allergic trigger?  The majority of these reactions are actually autoimmune.  This means that a patient has generated IgG antibodies directed against his/her own mast cells causing degranulation unrelated to any allergic trigger. This is a byproduct of a generalized immune response. If this child has an infection, his/her immune response is directed at making IgG antibodies against that particular pathogen. Once the immune system is revved up, antibodies are made to all kinds of things and this includes the auto antibodies against mast cells.

    • Interestingly, these autoantibody reactions can persist for weeks to months, in some cases, for years. The recommendation is to treat the child for as long as the hives have been going on. So, as outlined below, this means that if the hives have been persistent for a week, than a week of high dose antihistamine is reasonable.  If the antihistamine is stopped and the hives reappear, than the antihistamine is started again.

      • There is nothing to suggest that children with autoantibodies are at risk for other autoimmune diseases.  

  • What about a patient who gets an urticarial rash while taking an antibiotic? Again, timing is everything.  If frank urticarial lesions developed several days into a course of amoxicillin, it is most likely the underlying infection causing the rash and not the antibiotic. However, this child would be a candidate to be evaluated in an allergy clinic for penicillin skin testing.

    • The described “amoxicillin rash” is a morbilliform rash consistent of little red, flat, non-pruritic spots.

    • If there is concern for amoxicillin causing urticaria by virtue of a preexposure and the timing of the hives with this course of amoxicillin administration, then the next time this medication is needed, it could be given under observation in which a dose is given in the office and the child is observed for an hour.

  • How do you treat an urticarial reaction? Antihistamines are the drugs of choice.  While not actually keeping the mast cells from releasing histamines, these medications block the effect of the histamine on the histamine receptors. Interestingly, the difference in treatment failures is related to the dose of the antihistamine and not the particular class of antihistamine medication chosen.  

    • First line is often a non-sedating H1 antihistamine, such as cetirizine, and can be given as a typical dose one time per day. If this dose is not sufficient, instead of changing antihistamines and/or adding an H2 blocker, it is better to increase the dose of the initial antihistamine.

      • For cetirizine, for example, the typical adult or older child dose is 10 mg one time per day. If this is not working, it can be given  up to four times per day and it is safe to do so.

  • Are steroids indicated? If higher dose antihistamines are not sufficient in suppressing a child’s hives, that adding a corticosteroid such as prednisolone or prednisone is indicated at a dose of  1 mg/kg divided twice a day over 3-5 days.

  • Is there an association between hives and anaphylaxis? You can have hives are part of anaphylaxis, but there are other symptoms that are also present such as respiratory compromise and GI upset. For any child with anaphylaxis, an autoinjectable epinephrine device is imperative.  

    • Food, medication and insect triggered urticaria actually does require an autoinjectable epinephrine device to be prescribed when a trigger has been identified. The rationale is that there may be a subsequent accidental exposure and even though the first reaction was only urticarial in nature, a subsequent exposure may trigger a true anaphylactic reaction more than just hives. This is the exception and certainly not the rule.  

  • What are the top causes of urticaria in children? Again, the majority of hives are not allergy related. Very often, there is an underlying infection that has triggered the urticarial reaction. If you are suspecting food or medication, look for the temporal relationship between exposure and onset. The most common food triggers being milk, eggs, tree nuts, fish and legumes, such as peanuts. The most common medication triggers include the penicillin class.

    • Interestingly, as NSAIDs block the production of prostaglandins, and prostaglandins help to stabilize mast cells, given NSAIDs to a child who already has hives may make the hives worse. This, of course, does not mean the child is allergic to NSAIDs, but rather, the reaction is due to the pharmacologic property of the NSAID.

What is delayed pressure urticaria? This condition presents with a burning sensation and swelling at the site of heavy pressure. The onset is usually hours after the heavy pressure on the skin.

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