Diagnostic measures in patients with severe insect sting reactions and elevated baseline serum tryptase levels.

Mastocytosis or an elevated basal serum tryptase (bST) level are known risk factors for patients with insect venom allergy. We report on 3 patients with a history of severe anaphylactic insect sting reactions who underwent a detailed workup for insect venom allergy before starting venom immunotherapy. In addition to insect venom sensitization, an elevated concentration of bST (15.5, 20.8, and 23.2 µg/L) was found in all cases. There was no evidence of mastocytosis in the skin (MIS). Further testing revealed hereditary α-hypertryptasemia (HαT) in 2 patients and a D816V mutation by liquid biopsy in 1 patient, which is a minor diagnostic criterion for indolent systemic mastocytosis. Even without iliac crest puncture, causes of elevated bST can be narrowed down with minimally invasive diagnostic measures. As this has practical implications, patients with elevated bST should always undergo further work-up to determine the cause of this abnormal finding.

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© Dustri-Verlag Dr. K. Feistle.

Déclaration de conflit d'intérêts

FR has participated in advisory boards for ALK-Abelló Arzneimittel GmbH, Blueprint medicines (Germany), and received payments for lectures from ALK-Abelló Arzneimittel GmbH Novartis, and ThermoFisher. MW received payments for lectures from ALK-Abelló Arzneimittel GmbH. The other authors declare that there are no conflicts of interest in connection with this case report. Table 1.Characterization of the patients. Patient123Age at time of first presentation and biological sex47 yrs, male46 yrs, female34 yrs, femaleSting history: Type of insect, severity of sting reaction (Ring and Messmer)Wasp, repeated SAR (grade III) Wasp, SAR grade III Bee, SAR grade IIIInsect venom-specific IgE concentration at first presentation kUA/L (CAP class)Bee0.91 (2)0.15 (0)6.22 (3)Vespula0.55 (1)9.81 (3)0.05 (0)Lowest venom concentration resulting in a positive skin prick testBeeNegative up to 100 µg/mLNegative up to 300 µg/mLn.d.VespulaNegative up to 100 µg/mLNegative up to 300 µg/mLn.d.Intradermal test 1 μg/mLBeeNegativen.d.n.d.VespulaPositiven.d.n.d.bST (µg/L)20.8 23.215.5 Venom dose for initial treatment200 µg bee venom and 100 µg Vespula venom100 µg Vespula venom200 µg bee venomSymptoms during VITNo SARNo SARRepeated SAR (grade II) good tolerance of dosing-up while receiving omalizumab (for 5 months) Reactions after sting provocation/field sting n.d.SAR grade II following a field sting No SAR following VIT dose increase No SARbST (µg/L) during VIT20.2 17.216.3 TPSAB1 gene mutationGermline duplication Germline triplicationAbsentKIT mutation (D816V)AbsentAbsentPresentBone densitometry findingsNormalMild osteopenian.d.SAR = systemic allergic reaction; n.d. = not done; bST = basal serum tryptase; VIT = venom immunotherapy. Table 2.Criteria for the diagnosis of systemic mastocytosis [6]. Major criterionMultifocal dense infiltrates of mast cells in bone marrow biopsies and/or in sections of other extracutaneous organsMinor criteria≥ 25% of all mast cells in sections of bone marrow or other extracutaneous organs are atypical, e.g., spindle-shapedKIT-activating KIT point mutation at codon 816 in the bone marrow or another extracutaneous organCD2 and/or CD25 and/or CD30 expression on mast cellsBasal tryptase in serum > 20 µg/LIf at least 1 major and 1 minor criterion or 3 minor criteria are met, the diagnosis of a systemic mastocytosis is confirmed.