Empty mast cell syndrome: fallacy or fact?

Post-anaphylaxis mast cell anergy (PAMA), commonly referred to as 'empty mast cell (MC) syndrome', is a state of temporary loss of cutaneous MC reactivity in the immediate aftermath of anaphylaxis. Data relating to this condition are sparse and the incidence rate is currently unknown. PAMA has been described only in a few published case reports in the context of hymenoptera venom allergy and perioperative anaphylaxis. Best practice guidelines regarding optimal timing for performing skin tests postanaphylaxis are largely based on expert opinion, and allergy work-up has been recommended after 4-6 weeks postanaphylaxis to avoid false-negative results.This article provides a review of clinical literature surrounding PAMA, critically evaluates intracellular events in MCs from in vitro data and hypothesises regarding plausible immune mechanisms. There are no published data to directly explain molecular mechanisms underlying this phenomenon. Although not evidence based, PAMA has been attributed to depletion of MC granules following anaphylaxis. It is also plausible that exposure to high allergen concentrations in anaphylaxis can induce a temporary shift in MCs towards dominance of inhibitory signalling pathways, thus contributing to a state of transient hyporesponsiveness observed in some patients. Other potential contributory factors for reduced MC reactivity include downregulation of FcεRI expression, cross-linking of FcεRI to the inhibitory, low-affinity IgG receptors and administration of pharmacotherapeutic agents for anaphylaxis treatment. It is likely that this interesting phenomenon can be explained by a combination of these proposed mechanisms in addition to other genetic/host factors that have not yet been identified.

A Retrospective Critical Analysis and Risk Stratification of Penicillin Allergy Delabeling in a UK Specialist Regional Allergy Service.

BACKGROUND: A spurious label of penicillin allergy (Pen-A) negatively impacts on antibiotic stewardship and health care costs. Recent studies have proposed a guideline-steered direct penicillin challenge without undertaking allergy tests when "true allergy" is unlikely. OBJECTIVE: To critically analyze Pen-A clinical presentation, perform risk stratification, and determine clinical predictors for "true allergy." METHOD: Data were extracted retrospectively from clinical and electronic patient records. RESULTS: A total of 231 patients (M = 82; F =149; mean age 51.22 [standard deviation ± 18.07] years) were analyzed. Based on clinical history, patients were categorized as likely type I hypersensitivity reaction (HSR) (n = 27), likely type IV HSR (n = 65), indeterminate (n = 111), and HSR unlikely (n = 28). Based on an index reaction and comorbidities, patients were classified into "low risk" (n = 143) and "high risk" (n = 78). Pen-A was excluded in 74% of patients assessed having likely type I HSR, 91% with likely type IV HSR, 93% of indeterminate, and 100% of HSR unlikely patients. The negative predictive value for successful delabeling in the "low risk" group was 94% (odds ratio [OR] = 2.9; P = .02). Predictors for "true Pen-A" were history of anaphylaxis (OR = 30.6; P < .001), hospitalization (OR = 7; P < .001), ≤5 years since the index reaction (OR = 3; P = .04). CONCLUSIONS: Systematic clinical characterization and risk stratification has an important role in Pen-A delabeling. These data provide proof of concept for a guideline-based selection of patients labeled with Pen-A for a direct penicillin challenge. Patients in the "low risk" group seem suitable for this intervention, although a rigorous prospective evaluation is needed in a multicenter study.

Anaphylaxis and Clinical Utility of Real-World Measurement of Acute Serum Tryptase in UK Emergency Departments.

BACKGROUND: British guidelines recommend that serial acute serum tryptase measurements be checked in all adults and a subset of children presenting with anaphylaxis. This is the first study reporting the clinical utility of acute serum tryptase in a "real-world" emergency department (ED) setting following the publication of the World Allergy Organization (WAO) criteria for anaphylaxis. OBJECTIVES: To (1) assess sensitivity, specificity, and positive and negative predictive values (PPV, NPV) of acute serum tryptase in anaphylaxis; (b) determine factors associated with higher acute serum tryptase levels; and (c) audit compliance of acute serum tryptase measurement in the ED. METHODS: The methods used were retrospective electronic search for ED admissions to 3 acute care hospitals in Birmingham, UK, with anaphylaxis in 2012 using wide search terms followed by scrutiny of electronic clinical records and application of the WAO diagnostic criteria for anaphylaxis. Patients with an acute serum tryptase measurement were included in the analysis. RESULTS: Acute serum tryptase level was measured in 141 of 426 (33.1%) cases. Mean time from the onset of symptoms to the measurement of acute serum tryptase level was 4 hours 42 minutes (SD ± 05:03 hours) and no patients had serial measurements conforming to British guidelines. Acute serum tryptase level of more than 12.4 ng/mL (75th centile) was associated with a sensitivity, specificity, PPV, and NPV of 28%, 88%, 0.93, and 0.17, respectively. Multiple regression analysis showed that male sex (odds ratio, 2.66; P = .003) and hypotension (odds ratio, 7.08; P = .001) predicted higher acute serum tryptase level. CONCLUSIONS: An acute serum tryptase level of more than 12.4 ng/mL in an ED setting carries high PPV and specificity, but poor sensitivity and NPV.

Evaluation of AllergiSense Smartphone Tools for Adrenaline Injection Training.

Anaphylaxis is an increasingly prevalent life-threatening allergic condition that requires people with anaphylaxis and their caregivers to be trained in the avoidance of allergen triggers and in the administration of adrenaline autoinjectors. The prompt and correct administration of autoinjectors in the event of an anaphylactic reaction is a significant challenge in the management of anaphylaxis. Unfortunately, many people do not know how to use autoinjectors and either fail to use them or fail to use them correctly. This is due in part to deficiencies in training and also to the lack of a system encouraging continuous practice with feedback. Assistive smartphone healthcare technologies have demonstrated potential to support the management of chronic conditions such as diabetes and cardiovascular disease, but there have been deficiencies in their evaluation and there has been a lack of application to anaphylaxis. This paper describes AllergiSense, a smartphone app and sensing system for anaphylaxis management, and presents the results of a randomized, controlled, prepost evaluation of AllergiSense injection training and feedback tools with healthy participants. Participants whose training was supplemented with AllergiSense injection feedback achieved significantly better practiced injections with 90.5% performing correct injections compared to only 28.6% in the paper-only control group. In addition, the results provide insights into possible self-efficacy failings in traditional training and the benefits of embedding self-efficacy theory into the technology design process.