What is urticaria?
Urticaria is characterised by weals (hives) or angioedema (swellings, in 10%) or both (in 40%). There are several types of urticaria.
A weal (or wheal) is a superficial skin-coloured or pale skin swelling, usually surrounded by erythema (redness) that lasts anything from a few minutes to 24 hours. Usually very itchy, it may have a burning sensation.
Angioedema is deeper swelling within the skin or mucous membranes and can be skin-coloured or red. It resolves within 72 hours. Angioedema may be itchy or painful but is often asymptomatic.
Classification of urticaria
Urticaria is classified according to its duration.
Acute urticaria (< 6 weeks duration, and often gone within hours to days)
Chronic urticaria (> 6 weeks duration, with daily or episodic weals)
Chronic urticaria may be spontaneous or inducible. Both types may co-exist.
Who gets urticaria?
One in five children or adults has an episode of acute urticaria during their lifetime. It is more common in atopics. It affects all races and both sexes.
Chronic spontaneous urticaria affects 0.5–2% of the population; in some series, two-thirds are women. Inducible urticaria is more common. There are genetic and autoimmune associations.
What are the clinical features of urticaria?
Urticarial weals can be a few millimetres or several centimetres in diameter, coloured white or red, with or without a red flare. Each weal may last a few minutes or several hours and may change shape. Weals may be round, or form rings, a map-like pattern or giant patches.
Urticaria can affect any site of the body and tends to be distributed widely.
Angioedema is more often localised. It commonly affects the face (especially eyelids and perioral sites), hands, feet and genitalia. It may involve tongue, uvula, soft palate, or larynx.
In chronic inducible urticaria, weals appear about 5 minutes after the stimulus and last a few minutes or up to one hour. Characteristically, weals are:
Linear in symptomatic dermographism
Tiny in cholinergic urticaria
Confined to contact areas in contact urticaria
Diffuse in cold urticaria—if large areas of skin are affected, they can lead to fainting (potentially dangerous if swimming in cold water)
The weals are more persistent in chronic spontaneous urticaria, but each has gone or has altered in shape within 24 hours. They may occur at certain times of the day.
What causes urticaria?
Weals are due to release of chemical mediators from tissue mast cells and circulating basophils. These chemical mediators include histamine, platelet-activating factor and cytokines. The mediators activate sensory nerves and cause dilation of blood vessels and leakage of fluid into surrounding tissues. Bradykinin release causes angioedema.
Acute urticaria can be induced by the following factors, but the cause is not always identified.
Acute viral infection—upper respiratory infection, viral hepatitis, infectious mononucleosis, mycoplasma
Acute bacterial infection—dental abscess, sinusitis
Food allergy (IgE mediated)—usually milk, egg, peanut, shellfish
Drug allergy (IgE mediated)—often an antibiotic
Drug pseudoallergy—aspirin, nonselective nonsteroidal anti-inflammatory drugs, opiates, radiocontrast media; these cause urticaria without immune activation
Bee or wasp stings
Widespread reaction following localised contact urticaria — for example, rubber latex
Severe allergic urticaria may lead to anaphylactic shock (bronchospasm, collapse).Immune complexes due to blood transfusion cause serum sickness and certain drugs cause serum sickness-like reactions (urticaria leaving bruises, fever, swollen lymph glands, joint pain and swelling).
A single episode or recurrent episodes of angioedema without urticaria can be due to an angiotensin-converting enzyme (ACE) inhibitor drug.
Chronic spontaneous urticaria is mainly idiopathic (cause unknown). An autoimmune cause is likely. About half of investigated patients carry functional IgG autoantibodies to immunoglobulin IgE or high-affinity receptor FcεRIα.
Chronic spontaneous urticaria has also been associated with:
Chronic underlying infection, such as Helicobacter pylori, bowel parasites
Chronic autoimmune diseases, such as systemic lupus erythematosus, thyroid disease, coeliac disease, vitiligo and others
Weals in chronic spontaneous urticaria may be aggravated by:
Drug pseudoallergy—aspirin, nonsteroidal anti-inflammatory drugs, opiates
Food pseudoallergy—salicylates, azo dye food colouring agents such as tartrazine (102), benzoate preservatives (210-220) and other food additives
Inducible urticaria is a response to a physical stimulus.
What is the treatment for urticaria?
The main treatment of all forms of urticaria in adults and children is with an oral second-generation antihistamine chosen from the list below. If the standard dose (eg 10 mg for cetirizine) is not effective, the dose can be increased up to fourfold (eg, 40 mg cetirizine daily). They are stopped when the acute urticaria has settled down. There is not thought to be any benefit from adding a second antihistamine.
Although systemic treatment is best avoided during pregnancy and breastfeeding, there have been no reports that second-generation antihistamines cause birth defects. If treatment is required, loratadine and cetirizine are currently preferred.
Conventional first-generation antihistamines such as promethazine or chlorpheniramine are no longer recommended for urticaria:
Avoidance of trigger factors
In addition to antihistamines, the cause of urticaria should be eliminated if known (eg, drug or food allergy). Avoidance of relevant type 1 (IgE-mediated) allergens clears urticaria within 48 hours.
Treat identified chronic infections such as H pylori.
Avoid aspirin, opiates and nonsteroidal anti-inflammatory drugs (paracetamol is generally safe).
Minimise dietary pseudoallergens for a trial period of at least three weeks.
Avoid known allergens that have been confirmed by positive specific IgE/skin prick tests if these have clinical relevance for urticaria.
Cool the affected area with a fan, cold flannel, ice pack or soothing moisturising lotion.
The physical triggers for inducible urticaria should be minimised.
Symptomatic dermographism: reduce friction, eg avoid tight clothing.
Cold urticaria: dress up carefully in cold or windy conditions and avoid swimming in cold water.
Delayed pressure urticaria: broaden the contact area eg of a heavy bag.
Solar urticaria: dress up and apply broad-spectrum sunscreens.
Some patients with inducible urticaria benefit from daily induction of symptoms to induce tolerance. Phototherapy may be helpful for symptomatic dermographism.
Treatment of acute refractory urticaria
If non-sedating antihistamines are not effective, a 4 to 5-day course of oral prednisone (prednisolone) may be warranted in severe acute urticaria.
Intramuscular injection of adrenaline (epinephrine) is reserved for life-threatening anaphylaxis or swelling of the throat.
Treatment of chronic refractory urticaria
Patients with chronic urticaria that has failed to respond to maximum-dose second-generation oral antihistamines taken for four weeks should be referred to a dermatologist, immunologist or medical allergy specialist.
Taking the Next Step
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