D2.269 - Diagnostic challenges in evaluating diagnosis of mast cell disorder in a patient with severe allergy to hymenoptera venom

Mastocytosis is rare group of heterogeneous disorders characterized by the abnormal expansion and accumulation of mast cells (MCs) in one or more organs. Indolent systemic mastocytosis (ISM) is the most frequent form seen in adults, sometimes preceded by cutaneous involvement, called urticaria pigmentosa. Patients with ISM are at an increased risk to experience severe and frequent episodes of anaphylactic reactions, with hymenoptera venom allergy being the trigger of severe anaphylaxis in these patients.

We report the case of a 36-year-old female patient, working as a beekeeper, who was referred to our clinic in 2019 for confirmation of ISM diagnosis due to history of severe anaphylaxis reaction after honeybee sting. Initial allergy evaluation revealed high levels of specific IgE to Apis mellifera and increased basal serum tryptase levels. Bone marrow biopsy was inconclusive for being considered the major criterion for systemic mastocytosis confirmation and the c-KitD816V mutation was negative. The immunotherapy to hymenoptera venom was started and continued until present. During the up-dosing phase of immunotherapy, she presented three episodes of anaphylactic reaction, successfully resolved with systemic corticosteroids and omalizumab, well tolerated afterwards. She was intermittently stung few times resulting mild local reactions. Since about two years she noticed progressive onset of symptoms such mild cognitive impairment, generalised physical weakness, diffuse bone pain and progressively increased serum tryptase levels were recorded. We repeated the bone marrow biopsy which showed infiltrates of >15 mast cells expressing CD117 and CD25 positive spindle shaped mast cells, which allowed completion of diagnosis criteria and ISM confirmation.  

The reported case illustrates the challenges in diagnosis and managing systemic mastocytosis in clinical practice based on actual criteria and the need for evaluation by experienced pathologist in this field. Immunotherapy is a safe and effective treatment for patients with mastocytosis and venom allergy and has to be continued indefinite time.

Informed consent for publication was obtained from the patient.