Urticaria is a condition characterized by an itchy red skin rash (weals) and in some individuals can be associated with large swellings (angioedema).
Chronic urticaria (CU) is defined as weals that have been present persistently (with changing pattern of urticarial rash) or sporadically for at least 6 weeks. The weals of chronic spontaneous urticaria (CSU) develop with no external stimuli, distinguishing this condition from chronic inducible urticaria, where symptoms have an identifiable trigger such as physical pressure.
If the skin lesions last for more than 24 hours, leave bruising (staining) unrelated to scratching or where there are systemic symptoms (flu-like feelings, fever), urticarial vasculitis should be considered. A vasculitic condition may need confirmation by a skin biopsy.
Cutaneous mastocytosis (previously known as urticaria pigmentosa) is an uncommon condition and if the rash does not settle with antihistamines, then a serum tryptase may be informative in investigating this possibility.
The diagnosis of CSU is made clinically from the patient history (including drug history) and physical appearance of the skin lesions. Urticarial rashes persisting for days/weeks are unlikely to be allergy related although patients try to identify a food trigger that they can avoid. Bloods tests are not routinely required, but up to 30% of individuals are reported to have co-existing hypothyroidism.
The mainstay of treatment of CSU is second generation (non-sedating) antihistamines. The modern second-generation agents (e.g. cetirizine, desloratadine, fexofenadine, levocetirizine, loratadine) have fewer sedative effects. Fexofenadine is reported to cross the blood-brain barrier to a significantly lesser extent. The dosage may be increased by up to fourfold the licensed dose in order to maximise/optimise symptom control. The older sedating H1 antihistamines (e.g. hydroxyzine, diphenhydramine) are not generally recommended due to their anticholinergic and CNS effects. Anti H2 blockers probably do not offer additional therapeutic benefit once higher doses of ant1 H1 blockers (ranitidine) have been introduced.
Avoiding factors that can exacerbate CSU, including stress, alcohol, heat, and certain drugs (such as nonsteroidal anti-inflammatory drugs (NSAIDS) if the drug history suggests this) may be useful.
A short course of systemic corticosteroids can be helpful for acute exacerbations but are not recommended for long-term use.
In patients unresponsive to higher dose antihistamines, add-on therapies are available through specialist clinics, namely Omalizumab (a humanized IgG monoclonal antibody) and Ciclosporin.
Written by Professor Richard Powell, Professor of Clinical Immunology and Allergy