D1.188 - Adverse Reactions During Honey Bee Venom Immunotherapy as an Indicator of Underlying Clonal Mast Cell Disease Independent of Baseline Serum Tryptase: A Case Report

Background

Hymenoptera venom allergy represents the leading cause of anaphylaxis in adults in Europe. The association between severe insect sting reactions and mast cell disorders (MCD) have been demonstrated in numerous studies. Current recommendations suggest that patients with elevated baseline serum tryptase levels and/or severe systemic reactions to Hymenoptera stings should be evaluated for underlying mast cell disorders. Previous studies indicate that the adverse reactions are more frequent in patients with MCD compared to controls.

We report the case of a patient with normal baseline serum tryptase and a history of systemic reactions to honey bee stings that did not require medical intervention, who was subsequently diagnosed with systemic mastocytosis.

Case Presentation

A 31-year-old, female beekeeper with a history of systemic reactions to honey bee sting was referred to the allergy clinic for further evaluation. She had experienced two self-limiting systemic reactions following honey bee stings. The first reaction was characterized by tight feeling in the chest, gastrointestinal symptoms including vomiting and diarrhea, and flushing. Symptoms resolved rapidly after self-administration of oral antihistamine, and no medical care was sought. Following a subsequent sting, she again developed flushing and dyspnoea and immediately administered an oral antihistamine, with prompt resolution of symptoms. Diagnostic evaluation revealed in vitro sensitization to honey bee venom. In addition, uncontrolled asthma was identified and subsequently optimized. Baseline serum tryptase was within the normal range (10 µg/L). Venom immunotherapy (VIT) with honey bee venom was initiated. During VIT up-dosing, the patient developed recurrent flushing and dyspnea upon reaching a dose of 20,000 SQ units. At the time of the reactions, vital signs—including blood pressure, oxygen saturation, peak expiratory flow, and chest auscultation—were within normal limits. Nevertheless, intramuscular epinephrine and short acting beta agonist were administered due to clinical suspicion of a systemic reaction. A significant elevation in serum tryptase was documented on both occasions. The patient was referred to a hematologist, and a clonal mast cell disorder was diagnosed based on fulfillment of three minor diagnostic criteria. Further diagnostic evaluation due to suspicion of cutaneous and gastrointestinal involvement was initiated. Treatment with omalizumab was commenced, enabling continuation of VIT, and a maintenance dose of 60,000 SQ units was achieved without further systemic reactions.

Conclusion

Adverse reactions during venom immunotherapy may be indicative of an underlying MCD and warrant further diagnostic evaluation. This applies also to patients with normal baseline serum tryptase levels and in the absence of severe life-threatening reactions.