Urticaria

Urticaria is a common condition characterised by the sudden appearance of itchy, raised, erythematous skin lesions (wheals), with or without angioedema. It results from mast cell degranulation and histamine release in the dermis. It is classified by duration into acute (resolving within six weeks) and chronic (persisting beyond six weeks) forms, a distinction that shapes the diagnostic approach and management strategy.

Classification

Acute urticaria is common, frequently triggered by infection, food, medication or an identifiable allergen, and is generally self limiting.

Chronic spontaneous urticaria occurs without an identifiable external trigger, arising spontaneously and recurring daily or almost daily for more than six weeks, with an autoimmune mechanism (autoantibodies against IgE or the high affinity IgE receptor) identified in a substantial proportion of cases.

Chronic inducible urticaria is triggered by a specific identifiable physical stimulus, including dermographism (pressure), cold, heat, exercise, sunlight, vibration or delayed pressure, with the specific inducible subtype guiding both diagnostic testing and avoidance advice.

Individual wheals are typically intensely itchy, well demarcated, erythematous or pale centred with a surrounding flare, and characteristically transient, with any single lesion resolving within twenty four hours, though new lesions continue to appear elsewhere.

This is an important distinguishing feature from cutaneous vasculitis, where individual lesions persist beyond twenty four hours and typically resolve with residual pigmentation.

Angioedema, deeper swelling involving the subcutaneous and submucosal tissue, frequently accompanies urticaria and characteristically affects the lips, eyelids, tongue and, less commonly, the airway, and is typically not itchy but may be painful or produce a burning sensation.

Chronic spontaneous urticaria follows an unpredictable relapsing course, with symptoms present on most days for weeks to months or, in some patients, years, significantly impacting sleep and quality of life.

Chronic inducible urticaria produces wheals specifically in response to the relevant physical trigger, appearing within minutes of exposure and typically resolving within an hour, distinguishing it clinically from the spontaneous form.

Features suggesting an alternative diagnosis rather than ordinary urticaria include individual lesions persisting beyond twenty four hours, residual bruising or pigmentation, associated systemic symptoms (fever, arthralgia), or a burning rather than itching quality.

Any of these should prompt consideration of urticarial vasculitis or an autoinflammatory condition.

Diagnosis is clinical, based on the characteristic history and appearance of the lesions, with extensive investigation generally unnecessary for acute urticaria with an identifiable and resolving trigger.

Chronic spontaneous urticaria requires a more structured assessment, though routine extensive laboratory testing has limited yield in most cases.

Investigation should be guided by clinical features suggesting an underlying cause:

• full blood count and inflammatory markers as a reasonable baseline
• thyroid function and thyroid autoantibodies given a recognised association with autoimmune thyroid disease
• further targeted testing only where specific features suggest a particular underlying condition

Chronic inducible urticaria is diagnosed through specific provocation testing tailored to the suspected trigger, such as applying an ice cube to the skin for cold urticaria or performing a standardised exercise challenge for exercise induced urticaria.

Skin biopsy is reserved for atypical presentations, particularly where individual lesions persist beyond twenty four hours or there are associated systemic features, to exclude urticarial vasculitis.

A validated urticaria activity score, tracking the number of wheals and itch severity over consecutive days, is useful for objectively assessing disease severity and monitoring treatment response in chronic disease.

Second generation, non sedating antihistamines are first line treatment across both acute and chronic urticaria.

Chronic disease often requires dose escalation to two to four times the standard licensed dose before considering the response inadequate, a step frequently underutilised in practice before moving to second line therapy.

Avoidance of any identified trigger (specific food, medication, or physical stimulus in inducible urticaria) is straightforward and effective where a clear precipitant has been established.

Short courses of oral corticosteroids may be used for severe acute flares or significant angioedema, though are not recommended for long term management of chronic urticaria given cumulative toxicity without evidence of sustained benefit.

Omalizumab, an anti IgE monoclonal antibody, is highly effective second line therapy for chronic spontaneous urticaria not adequately controlled by high dose antihistamines, administered as a subcutaneous injection typically every four weeks.

Ciclosporin is used as a further option for antihistamine and omalizumab refractory chronic spontaneous urticaria, requiring monitoring of blood pressure and renal function given its adverse effect profile.

Leukotriene receptor antagonists are sometimes used as an adjunct, particularly where a component of the presentation suggests aspirin or nonsteroidal anti inflammatory drug sensitivity, though evidence for benefit as monotherapy is limited.

Angioedema affecting the airway, or any accompanying features of anaphylaxis, requires emergency management, distinct from the management of uncomplicated urticaria and angioedema without systemic compromise.

Patient education regarding the generally benign but often prolonged natural history of chronic spontaneous urticaria, together with reassurance and realistic expectation setting regarding the stepwise treatment approach, supports engagement with what is frequently a protracted management course.