Urticaria (hives)
Definition and clinical importance
Urticaria is a mast-cell driven cutaneous syndrome characterised by transient pruritic wheals and/or angio-oedema.
Mast-cell degranulation (IgE-dependent or non-IgE mechanisms) releases histamine and other mediators such as leukotrienes and prostaglandins, producing vasodilatation, increased microvascular permeability and sensory nerve stimulation. These mechanisms cause itchy, raised, erythematous or blanching wheals.
In emergency care the key task is to distinguish isolated cutaneous disease from systemic allergic reaction or anaphylaxis, because management differs markedly.
Pathophysiology
- Histamine causes vasodilatation and increased microvascular permeability, leading to transient dermal oedema (wheals).
- Pruritus results from sensory nerve stimulation.
- Angio-oedema is deeper dermal or submucosal oedema and may occur with or without wheals.
- Lesions typically migrate and resolve within hours; persistence for hours-days or painful lesions should prompt reconsideration of vasculitis or other diagnoses.
Classification
- Acute urticaria: duration less than 6 weeks (common triggers include infections, drugs, foods, insect stings; often idiopathic).
- Chronic spontaneous urticaria (CSU): daily or almost daily urticaria for 6 weeks or more without an external physical trigger.
- Chronic inducible urticaria: reproducible physical triggers such as cold, pressure, cholinergic, solar or vibratory stimuli.