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Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Urticaria & angioedema

Learning objectives
Clinical features
Investigations
Management
Activity

Learning objectives

Note: the diagnosis and management of anaphylaxis is not included in this topic.

Clinical features

Urticaria is composed of wheals: recurrent transient oedematous dermal papules and plaques, individual lesions persisting less than 24 hours. Wheals may be asymptomatic but are often intensely itchy or sting and burn. Angioedema results from oedema of dermis and subcutaneous tissue and accompanies urticaria in 40% of cases or occurs on its own in 10%.

Urticaria may be acute (<6 weeks duration) or chronic (>3 months). Several factors (cytokines and chemokines) are implicated in activation of mast cells receptors. Immunologic or non immunologic mechanisms elicit mediator releases and inflammatory activities inducing urticaria lesions.

Acute urticaria

The cause is unknown in most cases but some are due to IgE-mediated Type 1 hypersensitivity reactions i.e. allergy, and may progress to anaphylaxis – the rest are non-allergic in origin.

Allergens
  • Drugs in 5% (especially antibiotics)
  • Foods in 3% (eggs, milk, peanuts, shellfish)
  • Contact factors (latex, plants)
  • Bee and wasp stings
Non-allergic causes
  • Infections in 50% (UTI, respiratory tract virus, hepatitis)
  • Miscellaneous medical problems, especially connective tissue disease, thyroiditis, cancer
  • Drugs (especially opiates, aspirin, NSAID)
  • Foods (salicylates in fruit, additives such as tartrazine, benzoates, decomposing scombroid fish)

Angioedema

If intermittent angioedema occurs without urticaria, an ACE inhibitor may be responsible. Rarely, it is caused by inherited or acquired defects in C1 esterase inhibitor.

Urticaria
Acute urticaria
Urticaria
Chronic urticaria
Urticaria
Giant urticaria
Ordinary urticaria

Chronic urticaria

Anti-FceRI autoantibodies have been detected in about 60% of chronic urticaria cases, confirming chronic or ordinary urticaria to be an autoimmune disease in the majority of cases. It may be associated with chronic infection in others (helicobacter, candida, sinusitis, dental infection).

Angioedema may rarely be due to decreased C1-esterase inhibitor; in such cases there may be a family history. The presence of urticaria rules this out.

In many cases, no cause is found after careful history and investigation.

Physical urticaria

Physical urticaria accounts for 50% of cases of urticaria, and may coexist with idiopathic chronic urticaria. Physical urticaria results in localised short-lasting wheals (less than one hour). Physical urticaria may be due to:

Dermographism
Dermographism
Aquagenic urticaria
Aquagenic urticaria
Contact urticaria
Contact urticaria
Physical urticaria

Investigations

In most cases no investigations are warranted as the diagnosis is made by history and examination. In some cases a blood count is warranted (eosinophilia may point towards a drug allergy or parasitic infestation). Prick tests are rarely helpful but may be warranted for some food-related reactions. Interpretation can be difficult.

If the patient appears to have a severe allergy, for example food-related or food and exercise-related anaphylaxis, consider RAST Tests for potential causes particularly peanuts.

The autologous serum skin test can be used to identify autoimmune origin.

If angioedema in the absence of urticaria is recurrent, complement levels should be measured. C1 esterase inhibitor defects are associated with low levels of C4.

Management

Management should include avoidance of known precipitants. Antihistamines reduce itching, and to a lesser degree whealing, in most cases. However, it may take several days for antihistamines to take effect in acute urticaria. Newer generation antihistamines available in New Zealand include:

The dose may need to be increased. Conventional antihistamines such as promethazine, chlorpheniramine, azatidine and trimeprazine are less expensive and are sometimes prescribed for night sedation. They may cause anti-adrenergic and anticholinergic side effects, which may be particularly troublesome and prolonged in the elderly.

Oral steroids are often prescribed for 4 or 5 days for acute urticaria that is resistant to antihistamines (40mg daily), but they should not be prescribed in most cases of chronic urticaria.

Many other medications are used in chronic urticaria and are occasionally helpful, including:

Phototherapy or photochemotherapy (PUVA) may also be of benefit in selected patients.

Activity

What is the evidence that specific diets are useful in the management of chronic urticaria (e.g. avoiding salicylates and food additives, or low fat)?

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Author: Clin Assoc Prof Amanda Oakley

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