The basics - Urticaria

Identifying sub-types is clinically helpful, says Dr Laurence Knott.

Urticaria is a superficial swelling of the skin that results in a red raised itchy lesion. The underlying pathology is local dilation of capillaries and activation of mast cells, causing release of histamine and leakage of plasma from small blood vessels into the skin.

There is no universal classification system, but division into acute and chronic is clinically helpful. Acute urticaria occurs more frequently than chronic urticaria - 1 in 6 people at some point in their lives, compared with 1 in 1,000 people for chronic urticaria.1

Urticarial hives are most often caused by a non-allergic reaction

Diagnosis
The typical lesion is a wheal or hive. This presents as a white papule or plaque with surrounding erythema. Lesions vary in size, shape and number. If associated with swelling of the lips and tongue, a diagnosis of angio-neurotic oedema is made. Urticarial lesions are usually transient, disappearing after a few hours.

The British Association of Dermatologists has produced guidelines that help identify a number of different urticarial sub-types, based on clinical features and causes.2

  • Ordinary urticaria: separated into acute, chronic (six weeks or more) or episodic.
  • Physical urticarias (reproducibly induced by the same physical stimulus).
  • Mechanical: delayed pressure urticaria; symptomatic dermographism; or vibratory angio-oedema.
  • Thermal: cholinergic urticaria; cold contact urticaria; or localised heat urticaria.
  • Other: aquagenic urticaria; solar urticaria; exercise-induced anaphylaxis.
  • Angio-oedema without wheals may be idiopathic, drug-induced, or C1 esterase inhibitor deficiency.
  • Contact urticaria (allergens or chemicals).
  • Urticarial vasculitis (vasculitis on skin biopsy).
  • Autoinflammatory syndromes: hereditary; cryopyrin-associated periodic syndromes (CIAS1 mutations).
  • Schnitzler syndrome (chronic, non-pruritic urticaria in association with recurrent fever, bone pain, arthralgia or arthritis, and a monoclonal IgM gammopathy).

The diagnosis is usually made from the clinical appearance of the lesions, in addition to a short history of the lesions lasting a few hours.

Differential diagnoses to consider include eczema, erythema multiforme, dermatitis herpetiformis, urticarial vasculitis, pemphigoid and erysipelas.

Investigations are rarely necessary in mild cases, but may be required in patients who do not respond to treatment. IgE may be helpful in identifying allergic causes.

FBC, ESR and thyroid antibodies may be helpful in excluding inflammatory and autoimmune conditions. Factor C4 level may be needed to investigate the possibility of angioedema and to rule out rarer conditions such as urticarial vasculitis.

Management
Advice should be given about avoiding generalised aggravating factors such as heat and stress. Common specific allergens include food (nuts, strawberries, eggs), drugs (aspirin, NSAIDs, penicillins) and insect bites and stings.

A cause may only be found in about 50 per cent of cases.

Most patients respond to non-sedating H1 antihistamines. There are no meta-analyses comparing effectiveness, so choice is a matter of personal preference. If one fails, at least one other should be tried due to variability in response.

Sedating antihistamines may be considered if sleep disturbance is a problem, but should otherwise be avoided in view of their antimuscarinic effects.

Some patients may be helped by the addition of an H2 blocker (eg cimetidine) with or without a leukotriene antagonist (eg montelukast).

Calamine lotion might offer temporary relief, but some patients are irritated by the residue.

Rapid control of acute urticaria may be achieved by oral steroids, such as prednisolone 40mg for 3-5 days. Long-term steroids are not recommended for chronic urticaria.

Referral should be considered when urticaria fails to respond to treatment. Acute urticaria may require IV hydrocortisone, and chronic urticaria may require investigation to rule out an autoimmune cause.

Cases of persistent painful lesions and patients with angio-neurotic oedema should also be referred.

Prognosis
Acute urticaria is usually a one-off condition lasting 24-48 hours.

Most patients with chronic urticaria resolve after about six months.

A minority of patients continue to suffer from problems for years. Those presenting with angio-oedema and wheals seem to fare worse than those with wheals alone.

  • Dr Knott is a GP in Enfield, London

References

1. Humphreys F, Hunter J A. The characteristics of urticaria in 390 patients. Br J Dermatol 1998; 138: 635-8.

2. British Association of Dermatologists. Evaluation and management of urticaria in adults and children, 2007.

Further Reading

  • Urticaria: Clinical Knowledge Summary. 2007.
  • Grattan C, Powell S, Humphreys F. Management and diagnostic guidelines for urticaria and angiooedema. Br J Dermatol 2001; 144: 708-14.
  • BSACI. BSACI guidelines: Management of chronic urticaria and angio-oedema. British Society for Allergy and Clinical Immunology, 2007.

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