Mast cell activation syndrome: Importance of consensus criteria and call for research

Rare, Overlooked, or Underappreciated Causes of Recurrent Abdominal Pain: A Primer for Gastroenterologists

Recurrent abdominal pain is a common reason for repeated visits to outpatient clinics and emergency departments, reflecting a substantial unmet need for timely and accurate diagnosis. A lack of awareness of some of the rarer causes of recurrent abdominal pain may impede diagnosis and delay effective management. This article identifies some of the key rare but diagnosable causes that are frequently missed by gastroenterologists and provides expert recommendations to support recognition, diagnosis, and management with the ultimate aim of improving patient outcomes.

Idiopathic mast cell activation syndrome is more often suspected than diagnosed-A prospective real-life study

BACKGROUND

Idiopathic mast cell activation syndrome (MCAS) is characterized by three diagnostic criteria: (1) episodic mast cell (MC)-driven signs/symptoms of at least two organ systems in the absence of clonal MC expansion and definite triggers, (2) episodic increase in tryptase, and (3) response to MC-targeted treatment. Many patients believe they have MCAS, but how often this is the case remains unknown.

METHODS

We prospectively investigated patients with suspected MCAS (n = 100) for the diagnostic criteria including baseline tryptase, KIT D816V mutation, and patient-reported outcome measures (PROMs) over the course of 12 weeks. Comorbid depression and anxiety were explored with the Hospital Anxiety and Depression Scale (HADS).

RESULTS

In 53% of our patients (80% females), suspicion of MCAS was based on self-evaluation. In total, patients reported 87 different symptoms, mostly fatigue (n = 57), musculoskeletal pain/weakness (n = 49), and abdominal pain (n = 43), with overall high disease activity and impact. Two of 79 patients had increased tryptase (by >20% +2 ng/ml) following an episode. Only 5%, with any of the PROMs used, showed complete response to MC-targeted treatment. Depression and anxiety disorders were frequent comorbidities (n = 23 each), and 65 patients had pathological HADS values, which were linked to high disease impact and poor symptom control.

CONCLUSION

Mast cell activation syndrome was confirmed in only 2% of patients, which implies that it is not MC activation that drives signs and symptoms in most patients with suspected MCAS. There is a high need for comprehensive research efforts aimed at the identification of the true underlying pathomechanism(s) in patients with suspected MCAS.

Multifaceted MRGPRX2: New insight into the role of mast cells in health and disease

Cutaneous mast cells (MCs) express Mas-related G protein-coupled receptor-X2 (MRGPRX2; mouse ortholog MrgprB2), which is activated by an ever-increasing number of cationic ligands. Antimicrobial host defense peptides (HDPs) generated by keratinocytes contribute to host defense likely by 2 mechanisms, one involving direct killing of microbes and the other via MC activation through MRGPRX2. However, its inappropriate activation may cause pseudoallergy and likely contribute to the pathogenesis of rosacea, atopic dermatitis, allergic contact dermatitis, urticaria, and mastocytosis. Gain- and loss-of-function missense single nucleotide polymorphisms in MRGPRX2 have been identified. The ability of certain ligands to serve as balanced or G protein-biased agonists has been defined. Small-molecule HDP mimetics that display both direct antimicrobial activity and activate MCs via MRGPRX2 have been developed. In addition, antibodies and reagents that modulate MRGPRX2 expression and signaling have been generated. In this article, we provide a comprehensive update on MrgprB2 and MRGPRX2 biology. We propose that harnessing MRGPRX2's host defense function by small-molecule HDP mimetics may provide a novel approach for the treatment of antibiotic-resistant cutaneous infections. In contrast, MRGPRX2-specific antibodies and inhibitors could be used for the modulation of allergic and inflammatory diseases that are mediated via this receptor.

Selecting the Right Criteria and Proper Classification to Diagnose Mast Cell Activation Syndromes: A Critical Review

In recent years, knowledge about mechanisms underlying mast cell activation (MCA) and accumulation in various pathologic conditions increased substantially. In addition, criteria and a classification of MCA syndromes (MCASs) have been set forth. MCAS is defined by typical clinical symptoms, a substantial increase in serum tryptase level during an attack over the patient's baseline tryptase, and a response of the symptoms to drugs targeting mast cells, mediator production, and/or mediator effects. Alternative diagnostic criteria of MCAS have also been suggested, but these alternative criteria often lack specificity and validation. In this report, we critically review the contemporary literature relating to MCAS and compare the specificity, sensitivity, and strength of MCAS-related parameters within proposals to diagnose and classify MCAS and its variants. Furthermore, we highlight the need to apply specific consensus criteria in the evaluation and classification of MCAS in individual patients. This is an urgent and important medical necessity because as an increasing number of patients are being given a misdiagnosis of MCAS based on nonspecific criteria, which contributes to confusion and frustration by patients and caregivers and sometimes may delay recognition and treatment of correct medical conditions that often turn out to be unrelated to MCA.

Health-Related Quality of Life and Influencing Factors in Adults with Nonadvanced Mastocytosis-A Cross-Sectional Study and Qualitative Approach

BACKGROUND

Mastocytosis comprises a heterogeneous group of disorders characterized by an accumulation of mast cells in 1 or more organs. Symptoms range from mild complaints to severe and life-threatening events. Impact on quality of life seems to vary widely, but influencing factors are poorly understood so far.

OBJECTIVE

To examine impairments, psychological burden, health-related quality of life (HRQOL), and possible influencing factors in patients with mastocytosis.

METHODS

In semistructured telephone interviews, patients provided information on impairments in everyday life and psychological burden caused by mastocytosis. HRQOL was measured using the Mastocytosis Quality of Life (MC-QoL) questionnaire. Clinical data were collected from patient files.

RESULTS

A total of 101 adult patients with mastocytosis (74.3% women; mean age, 47.7 ± 13.5 years) were included. Half of the interviewed patients (50.6%) reported disease-related impairments in everyday life, and 42.4% stated a psychological burden. MC-QoL questionnaire scores showed a broad distribution, with a mean total score at a "mild" impairment level (mean total score, 34.7 ± 22.5). One-third of patients felt moderately (22.8%) or severely (13.9%) impaired, whereas one-third reported no impairment at all (30.7%). Symptoms of mast cell activation and perceived food intolerance had the highest impact on HRQOL. Higher age, higher body mass index, higher tryptase level, and longer duration of symptoms, as well as current drug therapy and pathological bone density, were each associated with reduced HRQOL.

CONCLUSIONS

A high level of suffering and strong associations between impairments and symptom-related factors indicate the importance of addressing patients' concerns and adequate symptom management in mastocytosis.

Depression, psychosocial correlates, and psychosocial resources in individuals with mast cell activation syndrome

Individuals with Mast Cell Activation Syndrome (MCAS), a rare chronic disease, experience unpredictable physical symptoms and diagnostic challenges resulting in poor emotional states. The prevalence and correlates of depressive symptoms were examined among 125 participants who completed the CES-D and relevant instruments. The majority reported a clinically-significant level of depression which was especially common among younger participants and those who reported greater loneliness or more disease-specific stressors. Greater magnitude of depressive symptoms was associated with greater illness intrusiveness, less social support, and lower optimism. Results highlight the value of interventions targeting loneliness and stressors unique to this population.

Doctor, I Think I Am Suffering from MCAS: Differential Diagnosis and Separating Facts from Fiction

Mast cell activation syndrome (MCAS) is a rare condition defined by a severe systemic reaction to mast cell (MC)-derived mediators. Most cases present with clinical signs of anaphylaxis, and some have an underlying IgE-dependent allergy. A primary MC disease (mastocytosis) may also be detected. Severe recurrent MCAS episodes requiring intensive care or even resuscitation are typically found in patients who suffer from both mastocytosis and allergy against certain triggers, such as hymenoptera venom components. A less severe form and a local form of MC activation (MCA) also exist. For these patients, diagnostic criteria are lacking. Moreover, a number of different, unrelated, conditions with overlapping symptoms may be confused with MCAS. As a result, many patients believe that they are suffering from MCAS but have in fact a less severe form of MCA or another underlying disease. In the current article, we review the potential differential diagnoses of MCA and MCAS and discuss available diagnostic criteria and diagnostic tools. These criteria and assays may be useful in daily practice and help avoid unnecessary referrals and unjustified fears in patients.

Using Baseline and Peak Serum Tryptase Levels to Diagnose Anaphylaxis: a Review

The diagnosis of anaphylaxis relies on a suggestive clinical history after exposure to a potential triggering factor. Serum tryptase concentrations increase on degranulation of mast cells and therefore serum tryptase levels are measured to diagnose anaphylaxis. There is no standardized method for assessing total serum mast cell tryptase (MCT) in anaphylaxis. The Working Conference in 2010 proposed a consensus equation (peak MCT should be > 1.2x baseline tryptase + 2 ng/L) to diagnose acute mast cell activation (aMCA). Our objective was to narratively review the literature since the Working Conference in 2010, examining the use of the consensus equation and other equations comparing baseline and peak serum tryptase during anaphylaxis. Computerized bibliographic searches of PUBMED and EMBASE were supplemented with a manual search of reference lists. English-language studies were included. Eleven studies met our inclusion criteria with a total of 4551 participants. However, only four studies with 653 participants used the consensus equation. The other seven studies used other methods to compare peak and baseline serum tryptase concentrations. Measuring serum tryptase levels is valuable in the diagnosis of anaphylaxis but is unable to detect all anaphylactic reactions. Based on our current literature review, the consensus equation is underused in the diagnosis of anaphylaxis. There is also a need for exploration of other biomarkers which could be used in parallel to peak and baseline serum tryptase measurements for further diagnostic certainty. Serum tryptase is the most studied biomarker in anaphylaxis but is still far from being the ideal biomarker for this. There is a need to identify new potential useful biomarkers. Serum tryptase levels are valuable in the diagnosis of anaphylaxis, but are unable to detect all anaphylactic reactions. Additionally serial tryptase measurements are laborious in daily clinical practice.

Utilization of the 2017 diagnostic criteria for hEDS by the Toronto GoodHope Ehlers-Danlos syndrome clinic: A retrospective review

The new 2017 diagnostic criteria for hypermobile Ehlers-Danlos Syndrome (hEDS) provide a framework for diagnosing hEDS but are more stringent than the previous Villefranche criteria. Our clinical experience at the GoodHope EDS clinic was that the 2017 criteria left many highly symptomatic patients without a diagnosis of hEDS. We conducted a retrospective cohort study to confirm our clinic experience and assess the accuracy of the 2017 diagnostic criteria for hEDS in patients who had a previous hEDS diagnosis based on the Villefranche criteria. Our study found that 15% (n = 20 of 131) of patients with a prior diagnosis of hEDS met the 2017 diagnostic criteria, and many of the traits used to distinguish hEDS were not significantly more frequent in patients who met 2017 criteria versus those who did not. In both groups objective systemic manifestations were found less frequently than subjective systemic manifestations. Beighton score (BS) as assessed by primary care practitioner was found to be higher than assessment by EDS practitioner in 81% (n = 74 of 91) of cases. Generalized joint hypermobility was confirmed in only 46% (n = 51 of 111) of patients who had a previous diagnosis of hEDS. Higher BS did not correlate with increased number of systemic manifestations in our cohort. Common comorbidities of hEDS were found with similar frequency in those who met 2017 criteria and those who did not. Based on our cohort, the 2017 hEDS diagnostic criteria require refinement to improve its diagnostic accuracy.

Frequency and prognostic impact of KIT and other genetic variants in indolent systemic mastocytosis

Indolent systemic mastocytosis (ISM) patients have a normal life expectancy, except in the 5% to 10% of cases that progress to more advanced SM (advSM), which has a significantly poorer outcome. Mutations in genes other than KIT frequently found in myeloid neoplasms have been associated with a poorer outcome among advSM, whereas limited information exists about their frequency and prognostic impact in ISM. We investigated the frequency and prognostic impact of variants in 18 genes, found to be altered in advSM, in 322 ISM patients (median follow-up, 5.7 years) divided into discovery (n = 200) and validation (n = 122) cohorts. Overall, 71 genetic variants were detected in 55 of 322 (17%) patients. Mutated ISM cases, particularly those carrying ASXL1, RUNX1, and/or DNMT3A (A/R/D) pathogenic variant allele frequencies (VAFs) ≥ 30%, exhibited significantly shortened (P < .001) progression-free survival (PFS) and overall survival (OS). Multivariate analysis showed that serum β2-microglobulin (sβ2M) levels > 2.5 µg/mL (hazard ratio [HR], 9.8; P = .001), together with a KIT D816V VAF ≥ 1% in bone marrow (BM) (HR, 10.1; P = .02) and pathogenic variants of A/R/D VAFs ≥ 30% (HR, 4.2; P = .02), were the best combination of independent predictors for PFS. In turn, A/R/D gene pathogenic VAF ≥ 30% was the only independent predictor for OS (HR, 51.8; P < .001). Based on these variables, 2 scoring systems were constructed for risk stratification of ISM at diagnosis with significantly different 10-year PFS (100%, 91%, 0% for scores of 0, 1, ≥2, respectively) and OS (100% and 50% for scores of 0 and 1) rates.

The Role of Leukotrienes as Potential Therapeutic Targets in Allergic Disorders

Leukotrienes (LTs) are lipid mediators that play pivotal roles in acute and chronic inflammation and allergic diseases. They exert their biological effects by binding to specific G-protein-coupled receptors. Each LT receptor subtype exhibits unique functions and expression patterns. LTs play roles in various allergic diseases, including asthma (neutrophilic asthma and aspirin-sensitive asthma), allergic rhinitis, atopic dermatitis, allergic conjunctivitis, and anaphylaxis. This review summarizes the biology of LTs and their receptors, recent developments in the area of anti-LT strategies (in settings such as ongoing clinical studies), and prospects for future therapeutic applications.

Why the 20% + 2 Tryptase Formula Is a Diagnostic Gold Standard for Severe Systemic Mast Cell Activation and Mast Cell Activation Syndrome

Mast cell activation syndrome (MCAS) is a condition characterized by recurrent episodes of clinically relevant, systemic, severe reactions to mast cell (MC)-derived mediators released in the context of anaphylaxis or another acute MC-related event. It is important to document MC involvement in these reactions in order to establish the diagnosis MCAS. The most specific and reliable marker of systemic MC activation is an acute and substantial event-related (transient) increase in the serum tryptase level over the individual's baseline value. However, the baseline level of tryptase varies depending on the underlying disease and the genetic background. For example, an estimated 3-5% of healthy individuals exhibit duplications or multiple copies of the TPSAB1 gene encoding for alpha-tryptase, and over 30% of all patients with myeloid neoplasms, including mastocytosis, have elevated basal tryptase levels. Therefore, it is of utmost importance to adjust the event-related diagnostic (MCAS-confirming) increase in tryptase over the individual baseline in a robust approach. To address this challenge, the 20% + 2 formula was proposed by the consensus group in 2012. Since then, this approach has been validated in clinical practice by independent groups and found to be sound. In the current article, we discuss the emerging importance and value of the 20% + 2 formula in clinical practice and its role as a criterion of severe systemic MC activation and MCAS.

Recent advances in our understanding of mast cell activation - or should it be mast cell mediator disorders?

INTRODUCTION

An increasing number of patients present with multiple symptoms affecting many organs including the brain due to multiple mediators released by mast cells. These unique tissue immune cells are critical for allergic reactions triggered by immunoglobulin E (IgE), but are also stimulated (not activated) by immune, drug, environmental, food, infectious, and stress triggers, leading to secretion of multiple mediators often without histamine and tryptase. The presentation, diagnosis, and management of the spectrum of mast cell disorders are very confusing. As a result, neuropsychiatric symptoms have been left out, and diagnostic criteria made stricter excluding most patients. Areas covered: A literature search was performed on papers published between January 1990 and November 2018 using MEDLINE. Terms used were activation, antihistamines, atopy, autism, brain fog, heparin, KIT mutation, IgE, inflammation, IL-6, IL-31, IL-37, luteolin, mast cells, mastocytosis, mediators, mycotoxins, release, secretion, tetramethoxyluteolin, and tryptase. Expert opinion: Conditions associated with elevated serum or urine levels of any mast cell mediator, in the absence of comorbidities that could explain elevated levels, should be considered 'Mast Cell Mediator Disorders (MCMD).' Emphasis should be placed on the identification of unique mast cell mediators, and development of drugs or supplements that inhibit their release.

Biomarkers in Human Anaphylaxis: A Critical Appraisal of Current Evidence and Perspectives

Anaphylaxis is a type I hypersensitivity reaction that is potentially fatal if not promptly treated. It is a clinical diagnosis, although measurement of serial serum total mast cell tryptase (MCT) is gold standard and may help differentiate anaphylaxis from its mimics. The performance characteristics of MCT assays in anaphylaxis has been variable in previous studies, due to multiple factors including differences in the definition of anaphylaxis, methods of MCT interpretation, clinical setting of anaphylaxis, causative agents, and timing of blood sample. An international consensus equation for MCT to interpret mast cell activation has been proposed and recently validated in the context of peri-operative anaphylaxis during general anesthesia. There has been an interest in the detection of newer biomarkers in anaphylaxis including platelet activation factor (PAF), chymase, carboxypeptidase A3, dipeptidyl peptidase I (DPPI), basogranulin, and CCL-2. The key determinants of an ideal biomarker in anaphylaxis are half-life, sample handling and processing requirements, and cost. There may be a role for metabolomics and systems biology in the exploration of novel biomarkers in anaphylaxis. Future studies applying these approaches might provide greater insight into factors determining severity, clinical risk stratification, identification of mast cell disorders and improving our understanding of this relatively complex acute immunological condition. Post mortem MCT evaluation is used in Forensic Medicine during autopsy for cases involving sudden death or suspected anaphylaxis. Interpretation of post mortem MCT is challenging since there is limited published evidence and the test is confounded by multiple variables largely linked to putrefaction and site of sampling. Thus, there is no international consensus on a reference range. In this state of the art review, we will focus on the practical challenges in the laboratory diagnosis of anaphylaxis and critically appraise (a) performance characteristics of MCT in anaphylaxis in different clinical scenarios (b) the role for novel biomarkers and (c) post mortem MCT and its role in fatal anaphylaxis.

Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome

Mast cell activation (MCA) accompanies diverse physiologic and pathologic processes and is one of the more frequently encountered conditions in medicine. MCA-related symptoms are usually mild and often transient. In such cases, histamine receptor blockers and other mediator-targeting drugs can usually control MCA. In severe cases, an MCA syndrome (MCAS) may be diagnosed. However, overt MCAS is an unusual condition, and many patients referred because of suspected MCAS are diagnosed with other diseases (autoimmune, neoplastic, or infectious) unrelated to MCA or suffer from MCA-related (eg, allergic) disorders and/or comorbidities without fulfilling criteria of an overt MCAS. These considerations are important as more and more patients are informed that they may have MCA or even MCAS without completing a thorough medical evaluation. In fact, in several instances, symptoms are misinterpreted as MCA/MCAS, and other clinically relevant conditions are not thoroughly pursued. The number of such referrals is increasing. To avoid such unnecessary referrals and to prevent misdiagnoses, we here propose a diagnostic algorithm through which a clinically relevant (systemic) MCA can be suspected and MCAS can subsequently be documented or excluded. In addition, the algorithm proposed should help guide the investigating care providers to consider the 2 principal diagnoses that may underlie MCAS, namely, severe allergy and systemic mastocytosis accompanied by severe MCA. Although validation is required, we anticipate that this algorithm will facilitate the management of patients with suspected MCAS.

Mast cell disorders: From infancy to maturity

Mast cells are typically linked to immediate hypersensitivity and anaphylaxis. This review looks beyond this narrow role, focusing on how these cells have evolved and diversified via natural selection promoting serine protease gene duplication, augmenting their innate host defense function against helminths and snake envenomation. Plasticity of mast cell genes has come at a price. Somatic activating mutations in the mast cell growth factor KIT gene cause cutaneous mastocytosis in young children and systemic mastocytosis with a more guarded prognosis in adults who may also harbor other gene mutations with oncogenic potential as they age. Allelic TPSAB1 gene duplication associated with higher basal mast cell tryptase is possibly one of the commonest autosomal dominantly inherited multi-system diseases affecting the skin, gastrointestinal tract, circulation and musculoskeletal system. Mast cells are also establishing a new-found importance in severe asthma, and in remodeling of blood vessels in cancer and atherosclerotic vascular disease. Furthermore, recent evidence suggests that mast cells sense changes in oxygen tension, particularly in neonates, and that subsequent degranulation may contribute to common lung, eye, and brain diseases of prematurity classically associated with hypoxic insults. One hundred and forty years since Paul Ehrlich's initial description of "mastzellen," this review collates and highlights the complex and diverse roles that mast cells play in health and disease.