Urticaria (hives) And Angioedema

Abstract

Urticaria and angioedema affect about 20% of the population at some point in their lives. The conditions frequently coexist and commonly reflect the same process occurring at different cutaneous levels.

The differential diagnoses of acute and chronic urticaria differ, with the majority of chronic cases being idiopathic. This article will describe an approach to identifying triggers of urticaria and angioedema and discuss principles of treatment.

Abbreviations Used

CIU: Chronic idiopathic urticaria, chronic spontaneous urticaria

CU: Chronic urticaria/angioedema

LTRA: Leukotriene receptor antagonist

NPV: Negative predictive value

NSAID: Nonsteroidal anti-inflammatory drug

PPV: Positive predictive value

RAST: Radioallergosorbent test

TCA: Tricyclic antidepressant

Introduction

Urticaria/angioedema are common problems in the pediatric population with a cumulative prevalence of about 20%. Their acuity is frightening to parents, they can be disfiguring, and the itch is distressing but when they occur without other systemic signs or symptoms they are rarely serious.

Pediatricians who understand the differential diagnoses of acute and chronic urticaria/angioedema, take a detailed history, use judicious testing, and apply evidence-based guidelines for treatment are able to reassure parents and families about the usually benign nature of the conditions. The aim of this paper is to provide a framework for the diagnosis and treatment of urticaria/angioedema.

Identifying Hives

Parents frequently consult the pediatrician because their child has hives but the rash is frequently gone before the patient’s office visit. Without the parent showing a picture of the rash on her smartphone, a description of the rash is often adequate for making the diagnosis. Urticaria are raised and well-circumscribed as the result of edema in the superficial dermis. True hives are transient with each individual lesion resolving within 24 hours without ecchymosis. The highly pruritic lesions with blanching erythema may be few or multiple. It is important to distinguish hives from non-urticarial conditions and from conditions causing pruritus without rash (Table 1).

Urticaria and angioedema may be IgE-mediated or non-IgE mediated. Sometimes the mechanism is unknown but in all cases, urticaria and angioedema occur as the result of mast cell activation with the release of preformed mediators of inflammation including histamine and tryptase, and the synthesis and release of newly-formed mediators.

Urticaria and angioedema coexist in about 15% of affected children and up to 10% of children have angioedema without urticaria. Because angioedema involves deeper dermal and subcutaneous tissues, it is not as well-demarcated or as pruritic as urticaria. IgE-mediated angioedema is also transient and usually asymmetric. The differential diagnoses of urticaria and angioedema are usually the same (see below). Therefore, for most patients, the two conditions reflect the same process occurring at different cutaneous depths. However, there are some conditions in which only urticaria or angioedema, but not both, occur (Table 2).

Acute Versus Chronic Urticaria and Angioedema

Chronic urticaria/angioedema (CU) are those lasting for more than 6 weeks. Although the frequency of urticaria/angioedema in those 6 weeks is not defined, the distinction from acute urticaria is important as the differential diagnoses vary. Hives of any duration can occur in any age or gender, but chronic urticaria is most common in young women. Up to 50% of CU resolve within 1 year of onset and 75% or more with 2-3 years. It is not uncommon for a patient with a history of CU to have recurrent episodes after months or years of quiescence.

Acute Urticaria and Angioedema - Differential Diagnosis

Acute urticaria and angioedema are by definition short-lived and resolve spontaneously within six weeks. Acute urticaria frequently results from immediate-type (Gell and Coombs Type 1) hypersensitivity reactions. At least 90% of reactions triggered by food in very young children are from cow’s milk, hen’s egg, soy, or wheat allergy. In older children and adults, peanut, tree nuts, shellfish, and finned fish account for more than 90% of new-onset food reactions. Any food can cause allergy, however, so careful history taking is necessary.

Medications are also common triggers to urticaria and angioedema. Antibiotics, NSAIDS, quaternary ammonium muscle relaxants, and latex are common IgE-mediated triggers. The penicillins are frequently implicated because they are commonly prescribed and are good haptens making them more allergenic than other classes of medication. The quaternary ammonium compounds are large molecules that easily cross-link mast-cell bound IgE molecules triggering mast cell activation. Opioids and radiocontrast media are non-specific mast cell activators that can trigger urticaria and angioedema in the absence of specific IgE. Angiotensin-converting enzyme inhibitors are also non-IgE mediated triggers of angioedema thorough mechanisms involving activation of the kinin system.

Bug bite and flying insect stings cause urticaria. Systemic reactions from Hymenoptera stings are IgE-mediated. Local reactions and papular urticaria from bug bites are not classic hives in that individual lesions last for greater than 24 hours. Pediatricians frequently see patients with post-viral urticaria, the mechanism of which is not known.

Finally and importantly, some acute urticaria and angioedema are idiopathic, without an identifiable preceding exposure.

Trigger identification in acute urticaria

The most specific and sensitive tool for identifying the trigger of acute urticaria/angioedema is a thorough history. Mast cell activation begins rapidly after cross-linking of surface-bound specific IgE. For instance, the onset of IgE-mediated food allergy reactions usually starts within 20-30 minutes, and almost always within 1-2 hours after ingestion. Therefore, history should focus on exposures and ingestions within a short time before the onset of symptoms. In addition, history should identify the presence or absence of cofactors that can increase the risk of hives including concurrent viral infections, NSAID use, and exercise.

Laboratory testing is sometimes indicated after a thorough history. In vitro and in vivo tests for specific IgE are useful to confirm or refute diagnostic suspicion after a detailed history. The true value of the tests comes with understanding their interpretation. A positive test does not indicate an allergy. It merely reflects sensitization, the presence of specific antibodies. IgE-mediated allergy is sensitization and mast cell activation with exposure; that is, there must be symptoms. Therefore, the physician should only request tests for specific IgE to allergens suggested by the history (rather than a “panel”). By so doing, the statistical value (sensitivity, specificity, positive [PPV] and negative predictive values [NPV]) of the tests improves.

In vitro tests (colloquially called RASTs [radioallergosorbent tests]) are easily accessible to any practitioner. RASTs are rarely used these days. Instead, in vitro tests that use the same immunologic principles but a different solid medium are preferred. The newer tests are more sensitive and specific than RASTs and in some cases, the sensitivity approaches that of skin tests. The degree of elevation in an in vitro test does not indicate the severity of allergy; it indicates a greater likelihood of allergy. Only the clinical reaction itself is predictive of severity. In vitro tests are more expensive than skin tests and take longer to get results. Because of the range of levels reported, they can also be harder to interpret. However, they are not influenced by antihistamine use, skin disease, or behavior of patents resistant to testing.

Skin testing is more specific and often easier to interpret than in vitro tests, but some of the same caveats apply. As within vitro tests, a positive test indicates sensitization, not an allergy. Food skin tests have a high NPV for IgE mediated reactions, but without a supportive history, positive tests to food have <50% PPV. As within Vitro tests, extensive testing without a supportive history is inappropriate. A larger positive skin test indicates a greater likelihood of allergy, but not the severity of the allergy. In contrast to in vitro tests, antihistamines and tricyclic antidepressants must be withheld before testing. Patients with atopic dermatitis and dermographism are more likely to have irrelevant or false positive tests.

Chronic Urticaria (Cu) and Angioedema - Differential Diagnosis

CU is present for six weeks or longer. Up to 90% of CU in children are idiopathic. They are virtually never allergic without a clear supportive history. Chronic idiopathic urticaria (CIU) is also called chronic spontaneous urticaria. About 1/3 of CIU are caused by an IgG autoantibody to the a-subunit of FceR1, the high-affinity IgE receptor in the surface of mast cells and basophils. Those cases are grouped under CIU, although in reality, they are not idiopathic because there is an identifiable cause. It is estimated that about half of CIU resolve spontaneously within a year and 75% within 2-3 years. Some patients have recurrent episodes of CIU and angioedema.

The next most common form of CU is those with physical triggers (Table 3). These inducible episodes might even be considered recurrent acute episodes as each individual occurrence is short-lived. However, many patients with CIU have an overlay of a physical trigger that leads to worsening.

The history is usually adequate for identifying physical urticaria, many of which are very rare. The most common physical hive is dermatographism (skin writing), easily demonstrable by lightly stroking or scratching the skin and observing for the appearance of a linear wheal. Cold-induced urticaria/angioedema frequently appears upon the rewarming of the skin. Patients commonly report hives while swimming or after coming out of the water or on exposed areas after being outdoors in the winter. Application of an ice cube to the forearm for 5-10 minutes and observing for wheal/flare with rewarming is a specific, but less sensitive test for diagnosis. Because urticaria, angioedema, and anaphylaxis are sometimes part of a spectrum, patients with cold-induced urticaria/angioedema, should be cautious when submerged in cold water. Familial cold-induced urticaria is very rare.

Cholinergic and exercise-induced urticaria are sometimes confused but are differentiated by history and physical appearances. Cholinergic urticaria occurs after exercise or after passive heating such as in saunas, sunbathing, etc. Individual punctate wheals are intensely pruritic with wide surrounding erythema that may coalesce. The onset of exercise-induced urticaria is independent of body temperature. The lesions appear more like classic urticaria. As with cold-induced urticaria, these patients are at risk of anaphylaxis. Therefore, they should not exercise vigorously alone and should have auto-injectable epinephrine available during exercise. Solar urticaria is very rare but may present as classic urticaria in sun-exposed areas. Type VI erythropoietic protoporphyria is a risk factor for solar urticaria.

On rare occasions in adults (<2%, of which most are vasculitis and not classic hives) and even more rarely in children, CU reflects the early presentation of an underlying systemic disease. Over the decades, numerous conditions have been associated with CU, but none so frequently that routine laboratory testing is necessary. However, the one test that everyone with urticaria/angioedema should have is a thorough and detailed history. If the review of systems is negative, the likelihood of a systemic disease presenting as urticaria becomes even more remote.

Table 1

Table 2

Table 3

Testing in Chronic Urticaria and Angioedema

Because most CU are idiopathic, most patients require no laboratory investigation. If the history or review of systems suggest any of the conditions in Table 1, an underlying systemic disease, or the hives and angioedema have atypical features testing should be directed towards the suspected condition. Of great importance, without a suggestive history of IgE-mediated trigger, testing for specific IgE is not indicated. Despite the lack of sensitivity of routine testing in CU without atypical features, many patients are not satisfied unless some testing is done. In those instances, many experts recommend screening with a CBC, ESR, LFTs, and TSH with any abnormal results being followed up as clinically indicated.

As noted above, about 1/3 of CIU patients have IgG autoantibodies to the a-subunit of FceR1. The utility of detecting the antibody has not been established because it does not affect treatment or outcome. Therefore, the use of autologous serum skin tests or in vitro tests for basophil histamine release, basophil activation markers, or for the antibody itself is not currently recommended.

Treatment of Urticaria and Angioedema

The mainstay of therapy of urticaria/angioedema is the H1 receptor blockade. Second-generation antihistamines are preferred because they are longer-acting and far less frequently sedating than the first-generation antihistamines. There is no antihistamine that is consistently better than another, so patients should the one that is most effective. A trial of several products might be necessary. A brief course of oral corticosteroids may shorten the duration and lessen the severity of severe cases and sometimes will abort an acute case. However, frequent or prolonged courses of oral steroids carry risk greater than the condition itself. Whenever possible (however impractical), cofactors to onset and triggers of physical urticaria should be avoided.

Treatment of CU is analogous to that of allergic airway disease in that a step-wise approach is taken with gradual steps down after consistent control is achieved. If monotherapy with a second-generation antihistamine (step 1) is only partially effective, higher/more frequent doses may provide further benefit. If higher doses are more effective, current studies indicate that second-generation antihistamines doses can be increased to as much as four times the usual recommended dose. Of course, if higher doses do not provide additional relief, they need not be continued. The addition of another second-generation antihistamine and/or a first-generation antihistamine at bedtime should also be considered. This “mix and match” approach often identifies a combination of antihistamines that provides the best relief.

Some patients with CU benefit from the addition of H2 blockers or leukotriene receptor antagonists (LTRAs). Only a small proportion of cutaneous histamine receptors are H2 receptors. It is possible their utility stems from competition for metabolic pathways, increasing serum H1-blocker levels. There are conflicting data regarding the effectiveness of LTRAs in CU. In poorly controlled CU, a trial of an LTRA might be considered. If there is no response in a short time, the LTRA can be discontinued.

Step 3 treatment recommends daytime use of hydroxyzine or doxepin. On a molar basis, the tricyclic antidepressants (TCAs) have a more potent antihistaminic effect than the antihistamines themselves. However, their high risk of sedation can limit their use. Gradually increasing daytime doses of first-generation antihistamines and TCAs allows some patients to accommodate to their soporific effects.

Step 4 therapy with alternative agents is reserved for patients with CU refractory to maximally tolerated antihistamine therapy. Omalizumab 150-300 mg SC q4weeks has been approved for patients 12 or older with CIU unresponsive to antihistamines and TCAs. Other alternative therapies including cyclosporine, dapsone, sulfasalazine, mycophenolate, and methotrexate have limited data supporting their utility. They appear to have moderate effects in some patients but there are not enough data to recommend their use until other treatments have failed.

Urticaria (Hives) and Angioedema - Conclusion

Urticaria and angioedema are common in pediatrics. A thorough history will usually identify if there is a potential preceding and avoidable trigger, especially in acute cases. The majority of CU are idiopathic or have a physical trigger. Without a supportive history of an IgE-mediated trigger or underlying systemic disease, testing is rarely indicated in acute or chronic cases.

Antihistamines are usually adequate to treat urticaria and angioedema, but finding the best antihistamine combination and dose can take some time.

Parents and patients should be instructed on trigger avoidance in acute urticaria and reassured about the benign nature and treatability of almost all CU.