Urticaria

Urticaria (commonly called hives) is a frequent skin condition, affecting up to 20% of people at some point. It is characterised by transient, itchy wheals caused by mast cell and basophil activation with release of histamine and other mediators. Episodes may be acute (<6 weeks, often allergic or infectious trigger) or chronic (>6 weeks, usually idiopathic or autoimmune).

🔑 Key point: Although usually benign and self-limiting, urticaria can overlap with angioedema and in severe cases precede anaphylaxis.

🧬 Aetiology & Pathophysiology

• 💥 Urticaria = transient mast cell & basophil activation → release of histamine, bradykinin, prostaglandins, and leukotrienes.
• 👉 These mediators cause vasodilation + ↑ capillary permeability 💧 → the classic wheal and flare reaction with itch and swelling.
• Immune-mediated:
  • Type I hypersensitivity (IgE-mediated: food, insect stings, drugs).
  • Type II/III (autoantibodies or immune complexes: autoimmune thyroid disease, SLE).
• Non-immune-mediated:
  • Direct mast cell degranulation: opioids, NSAIDs, radiocontrast, vancomycin (“red man”).
  • Physical urticarias: cold ❄️, heat 🔥, sunlight ☀️, vibration, pressure, exercise 🏃.

🩺 Clinical Features

• 🌸 Wheals: raised, erythematous, smooth lesions, intensely itchy 🤲, resolving within 24 h.
• ⏱️ Often appear in crops with pale centres and surrounding erythema.
• ✍️ Dermographism: wheals elicited by stroking or pressure.
• 💋 May be accompanied by angioedema (lips, eyelids, tongue, airway).
• 🚨 Severe cases can precede anaphylaxis → monitor for hypotension, stridor, wheeze.

🔎 Common Causes & Triggers

• Drugs 💊: penicillin, NSAIDs, ACE inhibitors, opioids, contrast media.
• Infections 🦠: viral (EBV, hepatitis), bacterial (streptococcus, H. pylori), parasites.
• Immune/Autoimmune 🧩: SLE, RA, autoimmune thyroid disease, cryoglobulinaemia.
• Physical 🌡️: cold, heat, sunlight, pressure, vibration, water 💦.
• Cholinergic urticaria: triggered by sweating, exertion, or emotional stress 😰.
• Idiopathic: the majority of chronic (>6 weeks) cases.

🧪 Investigations

• Usually a clinical diagnosis ✅.
• Chronic/recurrent: FBC, ESR/CRP, thyroid function + antibodies, autoimmune screen.
• Targeted: infection screen; C4/C1 inhibitor for suspected hereditary angioedema.

💊 Management

• 🚫 Avoid triggers: stop offending drug, treat infection, lifestyle modifications for physical urticaria.
• ✅ First-line: Non-sedating antihistamines (e.g. Cetirizine 10 mg OD, Loratadine 10 mg OD, Fexofenadine 180 mg OD). 👉 In chronic urticaria, doses can be escalated up to 4× daily if inadequate response (per BSACI/NICE guidance).
• 💊 Second-line / adjuncts: – Short oral prednisolone (30–40 mg OD × 3–5 days) for acute flares (avoid long-term). – Montelukast or H2 blockers may help in selected cases.
• 💉 Refractory chronic urticaria: Omalizumab (anti-IgE mAb) or ciclosporin under specialist supervision.
• 🚨 Anaphylaxis: IM adrenaline 0.5 mg (1:1000) into the anterolateral thigh → repeat every 5 min if needed. Oxygen, IV fluids, airway management, and hospital admission.

📚 Teaching Pearls

🧠 Differentiate: – Urticaria: superficial, itchy wheals resolving within 24 h. – Angioedema: deeper, often painful swelling (lips, tongue, eyelids), persisting longer.

💡 Exam favourite: ACE inhibitor → bradykinin-mediated angioedema (not histamine) → unresponsive to antihistamines or steroids.

🔎 Chronic urticaria (>6 weeks) is usually idiopathic, but always test for thyroid antibodies.

🧾 Clinical Cases

Case 1 – Acute allergic urticaria
A 22-year-old woman develops widespread itchy wheals within 30 minutes of eating prawns at a restaurant. She is otherwise well, with no swelling of lips or tongue. 👉 Diagnosis: IgE-mediated acute urticaria. 👉 Management: Non-sedating antihistamine, avoidance of shellfish. Monitor for progression.

Case 2 – Drug-induced urticaria
A 45-year-old man reports itchy red wheals after starting ibuprofen for back pain. Lesions resolve within 12 hours but recur after each dose. 👉 Diagnosis: NSAID-induced urticaria. 👉 Management: Stop NSAID, treat with antihistamine. Consider alternative analgesic (e.g. paracetamol).

Case 3 – Chronic urticaria
A 50-year-old woman presents with daily itchy wheals for 3 months. No obvious trigger. Bloods show raised thyroid peroxidase antibodies. 👉 Diagnosis: Chronic autoimmune urticaria. 👉 Management: Daily antihistamine (up-titrated if needed). Screen and manage thyroid disease. Refer if refractory (omalizumab/ciclosporin).

Case 4 – Urticaria with angioedema
A 30-year-old man has recurrent urticarial wheals with intermittent lip swelling lasting >24 h. Family history of similar symptoms. 👉 Consider: Hereditary angioedema (C1 esterase inhibitor deficiency). 👉 Management: Specialist referral. Antihistamines are ineffective; treat acute attacks with C1 inhibitor concentrate/icatibant.

Case 5 – Anaphylaxis
A 17-year-old student develops urticaria, lip swelling, stridor, wheeze, and hypotension minutes after a bee sting. 👉 Diagnosis: Anaphylaxis. 👉 Management: IM adrenaline 0.5 mg (1:1000) into the thigh, oxygen, IV fluids, airway support, hospital admission.