What is the cause of delayed local urticaria after allergen-specific immunotherapy (ASIT)?

From the Guidelines

Delayed local urticaria after allergen-specific immunotherapy is a common side effect that typically resolves on its own within 24-48 hours, and management should focus on alleviating symptoms while considering the potential for future systemic reactions, as indicated by studies such as 1. For management, applying a cold compress to the affected area and taking an oral antihistamine such as cetirizine 10mg or loratadine 10mg once daily until symptoms resolve can be beneficial.

• Local reactions are common, occurring in 26% to 82% of patients and 0.7% to 4% of injections, as reported in 1.
• These reactions are usually not bothersome, with 81.9% of patients deeming them not to be bothersome at all or only slightly bothersome, according to 1.
• For more significant reactions, a topical corticosteroid like hydrocortisone 1% cream applied twice daily for 2-3 days may help reduce inflammation.
• If the reaction is severe or persists beyond 72 hours, contacting the allergist is recommended as the immunotherapy dose may need adjustment, considering the findings of 1 that large local reactions might be associated with an increased risk for future systemic reactions.
• Before the next immunotherapy session, taking an antihistamine 1-2 hours beforehand may help prevent or minimize future reactions, based on general principles of allergy management.
• It is crucial to educate patients about the possible signs and symptoms of systemic reactions and to seek emergency medical attention if they occur, as emphasized in 1.
• The occurrence of delayed local urticaria does not typically indicate treatment failure, and these reactions often decrease in frequency and severity as treatment continues, as suggested by the general understanding of immunotherapy outcomes.
• Systemic symptoms like widespread hives, difficulty breathing, or dizziness require immediate medical attention, as they could indicate a more serious reaction, highlighting the importance of patient education and vigilance, as noted in 1.

From the Research

Delayed Local Urticaria after Allergen Specific Immunotherapy

• Delayed local urticaria can occur after allergen specific immunotherapy (SIT), with cases reported to occur 2-3 weeks after the last allergen injection 2.
• A study found that a 28-year-old man developed erythema, swelling, and pruritus at the SIT site after a treadmill exercise test, which lasted for one hour 2.
• The exact mechanism of delayed local urticaria after SIT is not fully understood, but it is thought to be related to an increased releasability of mast cells, even after more than 10 years 2.

Clinical Manifestations and Treatment

• Delayed systemic-allergic reactions to inhalant allergen immunotherapy can occur, with urticaria being the most common clinical manifestation 3.
• Treatment for chronic urticaria typically involves avoidance of triggers, second-generation H1 antihistamines, and adjunctive treatments such as first-generation H1 antihistamines, H2 antihistamines, and leukotriene receptor antagonists 4.
• In refractory chronic urticaria, patients may be referred to subspecialists for additional treatments, such as omalizumab or cyclosporine 4.

Long-term Efficacy of Allergen Immunotherapy

• Allergen immunotherapy has been shown to have long-term clinical benefits after treatment cessation, with both subcutaneous and sublingual immunotherapies modifying the underlying cause of the disease 5.
• A review of 10 randomized, double-blind, placebo-controlled clinical trials found that at least 3 years of allergen immunotherapy is recommended to achieve disease modification and sustained clinical and immunologic tolerance 5.