Fatal Anaphylaxis to Yellow Jacket Stings in Mastocytosis: Options for Identification and Treatment of At-Risk Patients.

BACKGROUND: Patients with indolent systemic mastocytosis (ISM) are at risk for severe anaphylactic reactions to yellow jacket (YJ) stings while demonstration of sensitization can be challenging because specific IgE (sIgE) levels are regularly below 0.35 kUA/L. The implication of missing YJ allergy is illustrated by a case of fatal anaphylaxis. OBJECTIVE: To explore the natural course of YJ venom allergy and the diagnostic accuracy and therapeutic consequence of YJ venom sIgE in patients with ISM. METHODS: All patients with ISM seen from 1981 to 2015 (n = 243) were evaluated on the number of YJ stings, reaction severity, and sensitivity and specificity of YJ venom sIgE. YJ venom allergic patients without mastocytosis served as control (n = 313). RESULTS: A total of 153 patients with ISM were stung during adult life. The first systemic reaction was more often severe in patients with ISM than in patients without mastocytosis (69.9% vs 22.0%) and reactions recurred in 40 of 41 re-stung patients with ISM. ISM reactors showed lower YJ venom sIgE levels than nonmastocytosis reactors (0.61 vs 4.83 kUA/L; P < .001) and asymptomatic sensitization was exceedingly rare. In ISM the current clinical threshold of 0.35 kUA/L yields a sensitivity and specificity of 77.6% and 87.5%, respectively. The optimal diagnostic accuracy is achieved at 0.17 kUA/L (sensitivity, 83.6%; specificity, 85.0%). CONCLUSIONS: The high rate of severe reactions and the fatal case underscore the importance of adequate diagnostic sensitivity of sIgE in patients with ISM. The sensitivity of sIgE can be ameliorated by lowering the threshold to 0.17 kUA/L, retaining good specificity. We recommend sIgE screening in all patients with ISM and discussing immunotherapy when YJ venom sIgE exceeds 0.17 kUA/L.

Diminished reliability of tryptase as risk indicator of mastocytosis in older overweight subjects.

BACKGROUND: Currently, measurement of serum tryptase level is the most commonly used test to estimate the need for bone marrow biopsy in patients suspected to have indolent systemic mastocytosis (ISM). Yet tryptase levels do not solely reflect the mast cell load and can be elevated by overweight, older age, and impaired renal function. The influence of these factors on urinary methylhistamine (MH) and methylimidazole acetic acid (MIMA) is still unknown. OBJECTIVE: We investigated the impact of age, body mass index (BMI), and kidney function on the diagnostic accuracy of tryptase, MH, and MIMA to select the most optimal test indicating the necessity of a bone marrow biopsy in ISM-suspected patients. METHODS: Retrospective data analysis of all adults in whom bone marrow investigations were performed because of high clinical suspicion and/or elevated tryptase, MH, or MIMA. RESULTS: 194 subjects were included. ISM was present in 112 and absent in 82 subjects (non-ISM). Tryptase was elevated by age and body weight in non-ISM subjects and by BMI in ISM subjects; however, these factors did not influence MH or MIMA. In the total study population, the diagnostic accuracy of tryptase, MH, and MIMA were comparable (area under the curve 0.80, 0.80, and 0.83). In subjects >50 years with a BMI >25 kg/m(2), the diagnostic accuracy of MIMA was higher compared with that of tryptase (area under the curve 0.93 vs 0.74; P = .011). CONCLUSION: In ISM-suspected patients >50 years with a BMI of >25 kg/m(2), MIMA has a greater value compared with tryptase in estimating the need for bone marrow biopsy.