Urticaria (hives) is a non-specific vascular response to a wide variety of stimuli. Commonly, acute urticaria has an allergic basis as a type I hypersensitivity state mediated by IgE. It can also be triggered by chemical and physical stimuli including cholinergic activity, sunlight, localized pressure, heat and cold. However, in more than 95% of patients, the exogenous cause can not be found. As many as 20% of persons probably experience the condition at some time in their lives. It is characterized by cutaneous wheals (erythematous, oedematous, pruritic papules) that blanch on pressure. Angio-oedema is a variant of urticaria that predominantly affects the mucous membranes. Most episodes of urticaria are transient and individual lesions may last for a few minutes to a few days, depending on the cause. The reaction can, however, become chronic and persist for many months.

Hereditary angio-oedema is a disease with an autosomal dominant trait. Large swellings may be triggered by trauma, including surgery. Since the lesions may involve the upper airways, there may be narrowing of the respiratory tract, a condition that requires emergency treatment. A hereditary angio-oedema-like syndrome sometimes occurs in patients with lymphoproliferative diseases, lymphosarcoma and chronic lymphocytic leukaemia.

Cholinergic urticaria is common in young adults after vigorous exercise or hot showers or under conditions of emotional stress. It can be accompanied by other signs of cholinergic activation including abdominal cramps, dizziness and wheezing. The lesions are usually confined to the trunk. Most regress within 30-60 minutes, but occasionally they are more persistent and coalesce.

Dermatographism is a very common form of urticaria. Wheals can be induced by scratching or rubbing of the skin and even by stimuli such as the beating of a hard shower stream.

Cold urticaria is characterized by localized pruritus, erythema and swelling which develop rapidly in response to a cold stimulus. Predisposed individuals risk shock, loss of consciousness and even death from drowning if they plunge into cold water.

Urticarial vasculitis, which is sometimes associated with systemic lupus erythematosus, has similar clinical features to urticaria but is a totally different condition resulting from a necrotizing vasculitis probably caused by the deposition of immune complexes. Because the wheals result from an inflammatory reaction, they tend to persist for a few days. Patients should be investigated for the presence of systemic lupus erythematosus.

Management

If there is obstruction of the airways, as in angio-oedema, this is considered a medical emergency and epinephrine, 1:1000 solution (0.5-1.0 ml), should be given intramuscularly. Occasionally dietary restriction is of value when the history is suggestive of food-induced urticaria. Acetylsalicylic acid and opioids should be avoided in patients with urticaria if they are suspected of being causative. While it is sometimes possible to relieve the underlying cause, in most cases reliance has to be placed on symptomatic treatment with antihistamines such as chlorphenamine and hydroxyzine. The new non-sedating antihistamines have the advantage of not interfering with daytime activities, but they are often not as effective for urticaria.

Selective desensitization, which may be directed to physical as well as chemical stimuli, is sometimes effective. For instance, frequent hot baths for patients with cholinergic urticaria and controlled graduated exposure to ultraviolet light for those with solar urticaria sometimes induce a useful measure of tolerance.