Initial assessment
The diagnosis of urticaria should begin with identification of suggestive signs and symptoms. Urticaria is characterised by erythematous pruritic wheals, usually with central pallor, of variable size and shape, which may coalesce and are migratory; each individual lesion resolves within 30 minutes to 24 hours, without bruising or residual pigmentation. Angioedema presents as sudden and pronounced swelling of the deep dermis/subcutaneous tissue, erythematous or skin-coloured, with paraesthesia, burning, tightness or pain rather than pruritus, and slow resolution, up to 72 hours.
Temporal classification
After clinical confirmation, the duration of symptoms should be determined: up to 6 weeks defines acute urticaria; duration longer than 6 weeks defines chronic urticaria. The pattern may be daily or intermittent and recurrent.
Angioedema without wheals
In recurrent angioedema without wheals, consider exposure to angiotensin-converting enzyme inhibitors. Other less frequent but possible drug classes include angiotensin receptor blockers, gliptins and neprilysin inhibitors. If symptoms remit after discontinuation of the angiotensin-converting enzyme inhibitor, this usually occurs within days, rarely up to 6 months. Persistence of symptoms after drug withdrawal should raise suspicion of hereditary or acquired angioedema due to C1 inhibitor deficiency; complement C4, C1 esterase inhibitor testing and possible genetic analysis are indicated, with referral to Allergy and Clinical Immunology.
Systemic signs
In the presence of unexplained recurrent fever, arthralgia or malaise, consider autoinflammatory urticarial syndromes. In these cases, request a full blood count, erythrocyte sedimentation rate and C-reactive protein to screen for systemic inflammation.
Urticarial vasculitis
If individual lesions persist on average for more than 24 hours, suspect urticarial vasculitis. Supporting features include persistent, non-evanescent episodes, tender or painful lesions rather than predominantly pruritic lesions, residual purpura or bruise-like discolouration, and associated symptoms such as fever, marked malaise, arthralgia, hypertension, proteinuria or haematuria. If suspected, skin biopsy of the lesions is indicated.
Inducible forms
Assess whether lesions are triggered by physical stimuli: cold urticaria, heat urticaria, pressure urticaria, solar urticaria, aquagenic urticaria, cholinergic urticaria (heat, exercise or sweating), contact urticaria and vibratory angioedema. Confirmation is performed with standardised provocation tests. If inducible, classify as chronic inducible urticaria; otherwise, as chronic spontaneous urticaria.
Differential diagnosis
In acute urticaria: atopic dermatitis, contact dermatitis, drug eruptions, insect bites, bullous pemphigoid, erythema multiforme minor, plant reactions, viral exanthems, auriculotemporal syndrome and Sweet syndrome. In chronic urticaria: urticarial vasculitis, papular urticaria, mastocytosis, autoinflammatory syndromes, C1 esterase inhibitor deficiency, systemic lupus erythematosus, polymorphic eruption of pregnancy, hypereosinophilic syndrome and anaphylaxis.
Investigation
In acute urticaria, because it is generally self-limiting, no additional investigation is required beyond a targeted history to identify triggers. Exceptions include suspected food allergy in sensitised patients or drug hypersensitivity, particularly to non-steroidal anti-inflammatory drugs, where skin prick testing, specific immunoglobulin E measurement to allergens and supervised oral challenge may be considered.
Treatment — first line
First-line treatment consists of second-generation H1 antihistamines taken regularly every day. First-generation antihistamines should not be used routinely because of central nervous system effects. If control is insufficient, the dose of the second-generation antihistamine may be increased progressively up to four times the usual dose, with reassessment every 2 to 4 weeks. After control is achieved, reduce gradually. In severe exacerbations, consider short and occasional courses of oral prednisolone as rescue therapy, approximately 0.5 mg/kg. Montelukast may be added in resistant cases, acknowledging the limited evidence.
Special populations
In children, consider screening for and treating parasitic infections when appropriate. Second-generation H1 antihistamines indicated between 2 and 11 years include cetirizine, levocetirizine, loratadine and rupatadine, with dose adjustment according to age and weight. During pregnancy and breastfeeding, when needed and after risk–benefit assessment, cetirizine or loratadine are preferred.
Second line
If symptomatic control remains insufficient despite optimisation of first-line treatment, consider second-line therapies such as omalizumab or ciclosporin in refractory patients and under specialist supervision.
