Urticaria and Angioedema — Written Clinical Reasoning

Part A — Chronic spontaneous urticaria with angioedema

Diagnosis and classification

The patient has chronic spontaneous urticaria (CSU) — daily transient wheals for more than 6 weeks, each lesion resolving within 24 hours (8 to 12 hours here), intensely pruritic, with associated angioedema (lip swelling). The individual lesion duration of less than 24 hours with complete resolution confirms ordinary urticaria rather than urticarial vasculitis (in which lesions last more than 24 hours, leave bruising, and are painful rather than pruritic). The history of Hashimoto thyroiditis places her in the subgroup with thyroid autoimmunity, present in 15 to 25 per cent of CSU patients. The worsening with ibuprofen reflects the pharmacologic NSAID-exacerbation mechanism (COX-1 inhibition shunting arachidonic acid toward leukotriene production), present in 20 to 30 per cent of CSU patients. ^[1]

Pathophysiology

CSU is a mast-cell-driven disease. Approximately 30 to 50 per cent of patients have functional IgG autoantibodies directed against the alpha subunit of the high-affinity IgE receptor (FceRI) or against IgE itself, which cross-link the receptor on mast cells and basophils and trigger degranulation. This autoimmune mechanism is the basis for the autologous serum skin test and for the response to immunomodulatory therapy. The wheals reflect histamine-mediated vasodilation and increased vascular permeability of the superficial dermal postcapillary venules. Because the swelling is histamine-mediated and accompanied by urticaria, the angioedema in this patient is histamine-mediated (NOT bradykinin-mediated) — the pivotal branch point that distinguishes it from hereditary or ACE inhibitor angioedema. ^[1]

Investigations — limited and targeted

The international EAACI guideline (Zuberbier 2022) recommends a limited panel: full blood count with differential (to exclude eosinophilia suggesting parasitic infestation or atopy), CRP or ESR (a raised value suggests urticarial vasculitis or systemic disease), and thyroid function with anti-TPO antibodies (because of the thyroid association). Extensive food and inhalant allergy testing is NOT indicated because CSU is not an IgE-mediated food allergy; broad panels produce false positives and drive unnecessary elimination diets. The autologous serum skin test or basophil activation test can confirm the autoimmune subgroup but rarely changes management because the treatment ladder is the same. ^[1]

Management — the four-step EAACI treatment ladder

Step 1. She is already on standard-dose cetirizine 10 mg daily with partial relief. Confirm regular daily (not PRN) dosing. ^[1]

Step 2. Up-titrate the cetirizine to up to four times the standard dose (up to 40 mg daily), stepwise over 2 to 4 weeks, assessing response at each dose. This up-titration is evidence-supported and the standard second step in the international guideline; it is the step most often missed. If cetirizine causes drowsiness at the higher dose, switch to fexofenadine (up to 720 mg daily), which is the least sedating. ^[1]

Step 3. If she remains symptomatic on up to 4-fold H1, add omalizumab 300 mg subcutaneously every 4 weeks — the licensed, guideline-preferred add-on. The ASTERIA II trial showed that 150 mg and 300 mg every 4 weeks significantly reduced itch and wheal activity; about 65 to 70 per cent of patients respond. ^[1]

Step 4. If she is refractory to omalizumab, add ciclosporin 2.5 to 4 mg per kg per day for 3 to 6 months, specialist-supervised, with blood pressure and renal monitoring. ^[1]

Adjuncts that are no longer routine steps: an H2 blocker (famotidine 20 to 40 mg twice daily — ranitidine is withdrawn for NDMA contamination) and montelukast 10 mg daily provide modest benefit in selected patients. Systemic corticosteroids are reserved for short rescue courses (prednisolone 0.5 mg per kg for 3 to 7 days) and are never maintenance. First-generation sedating antihistamines are explicitly NOT recommended for chronic use. ^[1]

Trigger avoidance and counselling

Advise the patient to avoid non-selective NSAIDs (ibuprofen here) permanently — a COX-2 selective inhibitor (celecoxib) is an alternative if an anti-inflammatory is needed, and paracetamol is safe. Treat the thyroid dysfunction on its merits (levothyroxine for hypothyroidism). Set the expectation that CSU is chronic but usually self-limiting — about half of patients remit within 1 to 5 years. Acknowledge the quality-of-life impact (sleep, work, mood) and screen for anxiety and depression. Explain plainly that CSU is an autoimmune mast cell activation, not a food allergy, to prevent the patient pursuing unnecessary elimination diets. ^[1]