Safety and effectiveness of immunotherapy in patients with indolent systemic mastocytosis presenting with Hymenoptera venom anaphylaxis

Background: Anaphylaxis after Hymenoptera sting has been described in patients with mastocytosis. Venom immunotherapy (VIT) is a safe and effective way to treat patients with Hymenoptera anaphylaxis, but few studies have addressed its usefulness in patients with systemic mastocytosis. Objective: To study the effectiveness and safety of VIT in patients with systemic mastocytosis having anaphylaxis after Hymenoptera sting. Methods: A total of 21 mastocytosis patients-4 women (19%) and 17 men (81%) with a median age of 50 years (range, 29-74 years)-with Hymenoptera sting anaphylaxis who were treated with VIT and followed for a median of 52 months (range, 2-250 months) were studied. Results: In 18 of 21 patients-16 of them lacking skin involvement-anaphylaxis was the presenting symptom. Six patients (29%) experienced adverse reactions during VIT, 3 during initiation and 3 during maintenance. Twelve patients (57%) were restung while undergoing VIT; 9 (75%) presented local reactions and 3 (25%) systemic reactions, 1 of which required intubation. The Hymenoptera specific IgE decreased from 4.15 kU/L (range, 0.44-100 kU/L) before immunotherapy to 1.2 kU/L (range, 0.34-69.4 kU/L) after 4 years (P<.003). Conclusion: Venom immunotherapy is effective to treat IgE-mediated Hymenoptera anaphylaxis in patients with mastocytosis. Its use is recommended despite a relatively high risk of adverse reactions during the build-up phase because it provides protection from anaphylaxis in around 3/4 of the patients.