Urticaria (hives)

Definition

Urticaria (hives) is characterised by transient, migratory, well-circumscribed, itchy wheals. They are caused by edema of the upper dermis and appear red, or less visibly red on deeply pigmented skin. Angiedema, swelling of the deeper dermis and subcutis, often occurs in addition.

Classification

• Acute urticaria: duration less than 6 weeks.
• Chronic urticaria: duration more than 6 weeks, divided into chronic spontaneous urticaria (without an identifiable external trigger) and chronic inducible urticaria with defined triggers.
• Inducible forms: cold, heat, delayed pressure, friction (urticarial dermographism), vibration, sunlight, water (aquagenic urticaria) and cholinergic urticaria triggered by sweating, e.g. through exercise, a warm bath or fever.

Occurrence & epidemiology

Acute urticaria is more common than chronic urticaria (about 70% versus 30%); its lifetime prevalence worldwide is about 20%. Fewer than 8% of acute cases progress to chronic urticaria. Chronic spontaneous urticaria is more common than the inducible form, affects about 1% of the world population and most often women aged 30 to 50.

Aetiopathogenesis

Mast cells and basophils in the upper dermis release histamine, bradykinin, kallikrein and other vasoactive substances, followed by vasodilation and intradermal edema.

• Immune-mediated: IgE-mediated type I reaction or autoimmunity. In chronic spontaneous urticaria, an autoallergic type (IgE against self-antigens such as thyroid peroxidase or IL-24) and an autoimmune type IIb (IgG against IgE or the high-affinity IgE receptor FcεRI) are distinguished.
• Non-immune: direct mast cell activation (e.g. by opioids, muscle relaxants or radiocontrast agents, partly via the receptor MRGPRX2), interference with cyclooxygenase by NSAIDs, complement activation and physical and emotional stimuli.
• Triggers of acute urticaria: drugs, foods (e.g. peanuts, tree nuts, fish, shellfish, wheat, eggs, milk, soy), insect stings, contact or inhaled allergens and infections (viruses, streptococci, Helicobacter pylori, parasites).
• Chronic urticaria: mostly idiopathic, followed in frequency by autoimmune causes; associations include autoimmune thyroiditis, systemic lupus erythematosus, Sjögren syndrome and cryoglobulinemia.

Clinical features

Wheals are usually red, dark pink or skin-colored and range from pinpoint size to large, confluent areas. They itch and disappear without residue while new ones appear elsewhere. In angiedema, mainly the face, lips, tongue, extremities or genitals swell; bowel involvement presents as colicky abdominal pain, and laryngeal or tongue edema can obstruct the airway. In inducible forms, wheals usually appear seconds to minutes after the stimulus.

Warning signs are breathlessness, stridor or wheezing, swelling of the face and tongue, fever, lymphadenopathy and wheals that last longer than 48 hours, are painful rather than itchy, are accompanied by purpura or vesicles or leave hyperpigmentation – the latter suggests urticarial vasculitis.

Diagnosis

• History: onset, duration and distribution of wheals, duration of individual lesions, angiedema, itching, exposures in the preceding 24 hours (drugs, foods, insects, animals, detergents, infections, stress) and atopic and autoimmune conditions.
• Acute, single episode: usually no laboratory tests unless a specific trigger is suspected.
• Chronic or recurrent urticaria: full blood count, blood chemistry, liver tests and TSH; targeted further tests if abnormal (e.g. thyroid autoantibodies, hepatitis serology, stool for parasites in eosinophilia).
• Challenge tests for suspected inducible urticaria: ice cube test (cold), stroking the skin with a blunt object (dermographism), pressure, heat, vibration or water.
• Allergy skin tests: when an allergic trigger is suspected and in unusual, recurrent or persistent cases.
• Skin biopsy: if the diagnosis is uncertain or wheals persist longer than 48 hours; urticarial vasculitis shows leukocytoclastic vasculitis.

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Further reading (open access)

1. MSD Manual Professional: Urticaria
2. StatPearls: Chronic Urticaria

Cross-references