Global Classification of Mast Cell Activation Disorders: An ICD-10-CM-Adjusted Proposal of the ECNM-AIM Consortium

Mast cell conditions and drug allergy: when to suspect and how to manage

PURPOSE OF REVIEW

Patients with mast cell disorders frequently experience symptoms from excessive mediator release like histamine and tryptase, ranging from mild flushing to severe anaphylactic responses. Hypersensitivity reactions (HRs) to drugs are a major cause of anaphylaxis in these patients, who often worry about triggering mast cell degranulation when taking medications. The aim of this review is to explore the complex interactions between mast cell disorders and drug HRs, focusing on the clinical challenges of managing these conditions effectively to enhance understanding and guide safer clinical practices.

RECENT FINDINGS

Among the drugs most commonly associated with hypersensitivity reactions in patients with mast cell disorders are non-steroidal anti-inflammatory drugs, antibiotics, and perioperative agents. Recent studies have highlighted the role of Mas-related G-protein coupled receptor member X2 (MRGPRX2) - a receptor involved in non-immunoglobulin E mediated mast cell degranulation - in exacerbating HRs. Investigations reveal varied drug tolerance among patients, underscoring the need for individual risk assessments.

SUMMARY

Tailored diagnostic approaches are crucial for confirming drug allergies and assessing tolerance in patients with mastocytosis, preventing unnecessary medication avoidance and ensuring safety before acute situations arise.

Mast cell activation syndrome: An up-to-date review of literature

Mast cells are a subtype of white blood cells and are involved in the immune system. These cells contain many chemical substances called mediators, which are involved in the allergic response. The fact that mast cells play a role in many events that require urgent intervention, especially anaphylaxis, has led to a more detailed study of these cells. The diseases also caused by dysfunctions of mast cells have been examined in many circumstances. For instance, mast cell activation syndrome is known as an augmented number of cells due to decreased cell death, resulting in clinical symptoms affecting many systems. The main common symptoms include flushing, hypotension, urticaria, angioedema, headache, vomiting and diarrhea. Although the underlying mechanism is not yet clearly known, we aim to review the literature in a broad perspective and bring together the existing knowledge in the light of the literature due to the diversity of its involvement in the body and the fact that it is a little known syndrome.

Mast cell activation and nutritional disorders in patients with hypermobility

PURPOSE OF REVIEW

Individuals with joint hypermobility disorders are increasingly referred to gastroenterology services for support with the investigation and management of gastrointestinal complaints. Individuals can present with a myriad of complex coexisting diagnoses, the inter-relationship of which is unclear. This review discusses the proposed association between hypermobile Ehlers-Danlos syndrome (hEDS) and hypermobility spectrum disorder (HSD) with disorders of mast cell activation and provides an overview of gastrointestinal symptoms and nutritional outcomes in this patient cohort.

RECENT FINDINGS

It is unclear whether a true association between hEDS/HSD and mast cell activation disorders exists. There is a high prevalence of nonspecific gastrointestinal symptoms in individuals with hEDS/HSD and patients may be at risk of macro-nutrient and micro-nutrient deficiencies, although the current evidence base is limited.

SUMMARY

We advocate a pragmatic approach to the investigation and management of gastrointestinal symptoms in patients with hEDS/HSD. This centres on excluding organic pathology, discussing the overlap with disorders of gut-brain interactions, trialling evidence-based therapies targeting individual symptoms, and supporting nutritional deficiencies where present via the least invasive approach. Engagement with a broad multidisciplinary team is also important to support the holistic needs of this patient cohort.

The Prevalence Of Osteoporosis Is Low in Adult Cutaneous Mastocytosis Patients

BACKGROUND

Systemic mastocytosis (SM) is a clonal disorder of mast cells (MCs) frequently associated with vertebral osteoporosis (OP) and subsequent vertebral fractures (VFs). The natural history of this OP remains unclear. Importantly, we do not know whether OP represents an early event triggered alongside MC abnormalities, and whether MC clonality is sufficient to trigger osteoporosis.

OBJECTIVE

To describe OP in patients with medullar clonality in cutaneous mastocytosis (CM) and monoclonal mast cell activation syndrome (MMAS) and to compare their osteoporosis characteristics with those of nonadvanced SM patients (bone marrow mastocytosis and indolent systemic mastocytosis).

METHODS

We retrospectively analyzed clinical, biological, and densitometric data of 27 CM, 13 MMAS, and 135 SM patients from the Mastocytosis Expert Center (CEREMAST) in Toulouse, France.

RESULTS

The OP (respectively 3.7, 30.8, and 34.1%) and VFs (0.0%, 15.4%, and 20%) were less frequent in CM than in MMAS and SM, despite the presence of clonal MCs in the bone marrow. Most patients with OP and VFs in the non-SM groups had the usual risk factors for OP. Interestingly, the only non-SM patient with a typical SM-like OP had high bone marrow tryptase, developed bone marrow KIT mutation during follow-up, and had a family history of SM. Our data show that OP is not a common clinical finding in CM but is frequent in MMAS. When OP and VFs occur in CM and MMAS patients, they differ from the usual phenotype of SM bone fragility.

CONCLUSIONS

Our findings suggest that, in most CM patients, the meaning and management of OP differs from that of OP in MMAS and nonadvanced SM. Prospective longitudinal studies and the validation of predictors are needed to identify CM and MMAS patients developing SM-related OP.

Dermatologic manifestations of hematologic disorders

Distinguishing key morphologic features and understanding the pathophysiology of common cutaneous manifestations of hematologic disorders is essential to ensure prompt and appropriate treatment. In fact, classic cutaneous signs may provide the first clue to the diagnosis of an underlying hematologic disease. Disorders of coagulation, vascular abnormalities, or cutaneous infiltration and deposition are responsible for the underlying pathophysiology of cutaneous manifestations in the majority of cases. Hematologists often feel ill-equipped in identifying morphologic changes in the skin. Thus, the purpose of this review is to provide a comprehensive overview of classic cutaneous manifestations and diagnostic considerations of the associated hematologic conditions. Though there is a specific focus on non-malignant disorders, those straddling the spectrum of malignancy are also discussed. In many disease states, the skin may serve as an important marker of an emerging hematologic disorder, so close collaboration and multidisciplinary input remain essential to provide optimal and timely care for these patients.

Mast cells in the autonomic nervous system and potential role in disorders with dysautonomia and neuroinflammation

Mast cells (MC) are ubiquitous in the body, and they are critical for not only in allergic diseases but also in immunity and inflammation, including having potential involvement in the pathophysiology of dysautonomias and neuroinflammatory disorders. MC are located perivascularly close to nerve endings and sites such as the carotid bodies, heart, hypothalamus, the pineal gland, and the adrenal gland that would allow them not only to regulate but also to be affected by the autonomic nervous system (ANS). MC are stimulated not only by allergens but also many other triggers including some from the ANS that can affect MC release of neurosensitizing, proinflammatory, and vasoactive mediators. Hence, MC may be able to regulate homeostatic functions that seem to be dysfunctional in many conditions, such as postural orthostatic tachycardia syndrome, autism spectrum disorder, myalgic encephalomyelitis/chronic fatigue syndrome, and Long-COVID syndrome. The evidence indicates that there is a possible association between these conditions and diseases associated with MC activation. There is no effective treatment for any form of these conditions other than minimizing symptoms. Given the many ways MC could be activated and the numerous mediators released, it would be important to develop ways to inhibit stimulation of MC and the release of ANS-relevant mediators.

Effective Doses of Low-Dose Naltrexone for Chronic Pain - An Observational Study

Purpose

Despite the availability of a wide variety of analgesics, many patients with chronic pain often experience suboptimal pain relief in part related to the absence of any medication to address the nociplastic component of common pain syndromes. Low-dose naltrexone has been used for the treatment of chronic pain, typically at 4.5 mg per day, even though it is also noted that effective doses of naltrexone for chronic pain presentations range from 0.1 to 4.5 mg per day. We performed an observational analysis to determine the range of effective naltrexone daily dosing in 41 patients with chronic musculoskeletal pain.

Methods

Charts of 385 patients, 115 males, 270 females, ages 18-92, were reviewed. Two hundred and sixty patients with chronic diffuse, symmetrical pain were prescribed a titrating dose of naltrexone to determine a maximally effective dose established by self-report of 1) reduction of diffuse/generalized and/or severity level of pain and/or 2) positive effects on mood, energy, and mental clarity. Brief Pain Inventory and PROMIS scales were given pre- and post-determining a maximally effective naltrexone dose.

Results

Forty-one patients met all criteria for inclusion, successfully attained a maximally effective dose, and completed a pre- and post-outcome questionnaire. Hormesis was demonstrated during the determination of the maximally effective dosing, which varied over a wide range, with statistically significant improvement in BPI.

Conclusion

The maximally effective dose of low-dose naltrexone for the treatment of chronic pain is idiosyncratic, suggesting the need for 1) dosage titration to establish a maximally effective dose and 2) the possibility of re-introduction of low-dose naltrexone to patients who had failed initial trials on a fixed dose of naltrexone.

Low Prevalence of Idiopathic Mast Cell Activation Syndrome Among 703 Patients With Suspected Mast Cell Disorders

BACKGROUND

Idiopathic mast cell activation syndrome (iMCAS) is characterized by severe, episodic systemic mast cell (MC) activation and mediator-related symptoms, an event-related increase in serum tryptase levels, and response to MC-targeted therapies in the absence of underlying IgE-mediated allergy or clonal MC disorder. Studies indicating its prevalence using evidence-based diagnostic criteria are lacking.

OBJECTIVE

To assess the prevalence and clinical and laboratory features of patients with iMCAS.

METHODS

We conducted a retrospective evaluation of data from 703 consecutive patients (aged ≥18 years) referred to our center based on suspicion of having MC disorders. Patients underwent a thorough clinical workup including patient history, allergy tests, KIT D816V mutation analysis, and/or bone marrow investigation. Disease activity was prospectively assessed during follow-up visits.

RESULTS

We identified 31 patients with confirmed iMCAS. Furthermore, hereditary α-tryptasemia was detected in three patients with baseline tryptase levels greater than 8 ng/mL. The most common clinical presentation during MCAS episodes was mucocutaneous symptoms in patients with iMCAS, especially urticaria or angioedema. However, these symptoms were less prevalent in patients with clonal MCAS (P = .015). The duration of diagnostic delay was significantly longer in patients with iMCAS compared to those with clonal MCAS (P = .02).

CONCLUSIONS

The overall prevalence of iMCAS was 4.4% in the entire cohort, which indicates that iMCAS is an uncommon condition. To accurately diagnose iMCAS, it is crucial to evaluate suspected patients using the three diagnostic MCAS criteria. This involves performing a comprehensive allergy work-up including laboratory tests and ultrasensitive mutation analysis of KIT D816V. Subsequently, recommended diagnostic algorithms should be applied.

Reversible Elevation of Tryptase Over the Individual's Baseline: Why is It the Best Biomarker for Severe Systemic Mast Cell Activation and MCAS?

PURPOSE OF REVIEW

Mast cell (MC) activation syndromes (MCAS) are conditions defined by recurrent episodes of severe systemic anaphylaxis or similar systemic events triggered by MC-derived mediators that can be measured in biological fluids. Since some symptoms of MC activation may occur due to other, non-MC etiologies and lead to confusion over diagnosis, it is of crucial importance to document the involvement of MC and their products in the patients´ symptomatology.

RECENT FINDINGS

The most specific and generally accepted marker of severe systemic MC activation is an event-related, transient increase in the serum tryptase level over the individual baseline of the affected individual. However, baseline concentrations of serum tryptase vary among donors, depending on the genetic background, age, kidney function, and underlying disease. As a result, it is of critical importance to provide a flexible equation that defines the diagnostic increase in tryptase qualifying as MCAS criterion in all patients, all situations, and all ranges of baseline serum tryptase. In 2012, the consensus group proposed the 120% + 2 ng/ml formula, which covers the great majority of groups, including cases with low, normal, or elevated basal serum tryptase level. This formula has been validated in subsequent studies and has proven to be a robust and consistent diagnostic criterion of MCAS. The present article is discussing the impact of this formula and possible limitations as well as alternative markers and mediators that may be indicative of MCAS.

Mast Cell-Targeting Therapies in Mast Cell Activation Syndromes

PURPOSE OF REVIEW

Provide an overview of the expanding landscape of mast cell (MC)-targeting treatments in mast cell activation syndromes (MCAS).

RECENT FINDINGS

Tyrosine-kinase inhibitors (TKIs) targeting wild-type and mutated KIT can efficiently induce MC depletion. Avapritinib and midostaurin can also temper IgE-mediated degranulation. Avapritinib has been recently approved by the FDA for the treatment of indolent systemic mastocytosis (ISM). Targeting activation pathways and inhibitory receptors is a promising therapeutic frontier. Recently, the anti Siglec-8 antibody lirentelimab showed promising results in ISM. MCAS is a heterogeneous disorder demanding a personalized therapeutic approach and, especially when presenting as anaphylaxis, has not been formally captured as outcome in prospective clinical trials with TKI. Long-term safety of TKI needs to be addressed. New drugs under investigation in diseases in which non-neoplastic MCs play a pivotal role can provide important inputs to identify new efficient and safe treatments for MCAS.

Using the Right Criteria for MCAS

PURPOSE OF REVIEW

The current article aims to provide a comprehensive update on diagnostic criteria for mast cell activation syndrome (MCAS), addressing challenges in diagnosing and classifying MCAS and its variants.

RECENT FINDINGS

In recent years, there has been a significant increase in our knowledge regarding the underlying mechanisms responsible for the activation of mast cells (MCs) in various pathological conditions. Furthermore, a set of criteria and a classification for MCASs have been established. MCAS is characterized by the presence of typical clinical symptoms, a substantial elevation in serum tryptase levels during an attack compared to the patient's baseline tryptase levels, and a response to MC mediator-targeting therapy. In this report, a thorough examination was conducted on the contemporary literature relating to MCAS, with a focus on comparing the specificity, sensitivity, and robustness of MCAS-related parameters within proposals for diagnosing and classifying MCAS and its variants. Moreover, the significance of employing specific consensus criteria in the assessment and categorization of MCAS in individual patients was underscored, due to the escalating occurrence of patients receiving a misdiagnosis of MCAS based on nonspecific criteria.

Challenges in Drug and Hymenoptera Venom Hypersensitivity Diagnosis and Management in Mastocytosis

Mastocytosis is a myeloproliferative neoplasm characterized by abnormal proliferation and activation of clonal mast cells typically bearing the KITD816V mutation. Symptoms manifest due to the release of bioactive mediators and the tissue infiltration by neoplastic mast cells. Mast cell activation symptoms include flushing, pruritus, urticaria, abdominal cramping, diarrhea, wheezing, neuropsychiatric symptoms, and anaphylaxis. Up to 50% of patients with mastocytosis report a history of provoked and unprovoked anaphylaxis, with Hymenoptera venom and drugs the most common culprits. NSAIDs, antibiotics, vaccines, perioperative medications, and radiocontrast media are often empirically avoided without evidence of reactions, depriving patients of needed medications and placing them at risk for unfavorable outcomes. The purpose of this review is to highlight the most common agents responsible for adverse drug reactions in patients with mastocytosis, with a review of current epidemiology, diagnosis, and management of drug hypersensitivity and Hymenoptera venom allergy.

Diagnostic Significance of Tryptase for Suspected Mast Cell Disorders

Tryptase has proven to be a very useful and specific marker to demonstrate mast cell activation and degranulation when an acute (i.e., within 4 h after the event) and baseline value (i.e., at least 24 h after the event) are compared and meet the consensus formula (i.e., an increase of 20% + 2). The upper limit of normal determined by the manufacturer is 11.4 ng/mL; however, this boundary has been the subject of debate. According to ECNM and AIM experts, the normal range of baseline tryptase should be 1 to 15 ng/mL. A genetic trait, hereditary alpha tryptasemia, characterized by an increased alpha coding TPSAB1 copy number is associated with a baseline value above 8 ng/mL. Elevated tryptase can also be found in chronic kidney disease, obesity, and hematological neoplasms. A tryptase > 20 ng/mL serves as a minor criterion to diagnose systemic mastocytosis and an increase in tryptase > 20% + 2 during an acute event is a required criterion in the diagnosis of mast cell activation syndrome. The goal of this review is to demonstrate the (in)significance of tryptase using some clinical vignettes and to provide a practical guide on how to manage and interpret an elevated tryptase level.

World Health Organization Classification and Diagnosis of Mastocytosis: Update 2023 and Future Perspectives

Experts of the European Competence Network on Mastocytosis (ECNM) and the American Initiative on Mast Cell Disorders have discussed and updated diagnostic criteria and the classification of mastocytosis, based on new insights in the field and data collected in recent years, mostly within ECNM registry projects in which studies on several thousand cases have been performed. Based on this proposal, the World Health Organization has updated its classification of mastocytosis. This article discusses the revised classification of mastocytosis in light of a rapidly moving field and the advent of new diagnostic parameters, new prognostication tools, and new therapies.

A Puzzling Mast Cell Trilogy: Anaphylaxis, MCAS, and Mastocytosis

Our knowledge of biology and mast cell (MC) function, as well as disorders associated with the pathologic activation of MCs, has evolved over the last few decades. Anaphylaxis, mast cell activation syndrome (MCAS), and mastocytosis are interrelated yet distinct conditions within the spectrum of mast cell activation disorders. Nevertheless, all three conditions can co-exist in one and the same patient, as pathologic MC activation is the key finding in all three. When mediator release is excessive and involves multiple systems, anaphylaxis and MCAS may occur. Furthermore, mastocytosis is a clonal disorder of MCs and often presents with anaphylaxis and MCAS. Nevertheless, in some cases, even the proliferative and accumulative features of MCs in mastocytosis can account for symptoms and disease progression. In each case, diagnosis can be only made when the diagnostic consensus criteria are fulfilled. The current article aims to provide a concise clinical update and pinpoint the main difficulties in diagnosing these puzzling disorders of MCs in medical practice.

Mast Cell Activation Syndrome Update-A Dermatological Perspective

Mast cells (MCs) are infamous for their role in potentially fatal anaphylaxis reactions. In the last two decades, a more complex picture has emerged, as it has become obvious that MCs are much more than just IgE effectors of anaphylaxis. MCs are defenders against a host of infectious and toxic aggressions (their interactions with other components of the immune system are not yet fully understood) and after the insult has ended, MCs continue to play a role in inflammation regulation and tissue repair. Unfortunately, MC involvement in pathology is also significant. Apart from their role in allergies, MCs can proliferate clonally to produce systemic mastocytosis. They have also been implicated in excessive fibrosis, keloid scaring, graft rejection and chronic inflammation, especially at the level of the skin and gut. In recent years, the term MC activation syndrome (MCAS) was proposed to account for symptoms caused by MC activation, and clear diagnostic criteria have been defined. However, not all authors agree with these criteria, as some find them too restrictive, potentially leaving much of the MC-related pathology unaccounted for. Here, we review the current knowledge on the physiological and pathological roles of MCs, with a dermatological emphasis, and discuss the MCAS classification.

European Competence Network on Mastocytosis (ECNM): 20-Year Jubilee, Updates, and Future Perspectives

In 2002, the European Competence Network on Mastocytosis (ECNM) was launched as a multidisciplinary collaborative initiative to increase the awareness and to improve diagnosis and management of patients with mast cell (MC) disorders. The ECNM consists of a net of specialized centers, expert physicians, and scientists who dedicate their work to MC diseases. One essential aim of the ECNM is to timely distribute all available information about the disease to patients, doctors, and scientists. In the past 20 years, the ECNM has expanded substantially and contributed successfully to the development of new diagnostic concepts, and to the classification, prognostication, and treatments of patients with mastocytosis and MC activation disorders. The ECNM also organized annual meetings and several working conferences, thereby supporting the development of the World Health Organization classification between 2002 and 2022. In addition, the ECNM established a robust and rapidly expanding patient registry and supported the development of new prognostic scoring systems and new treatment approaches. In all projects, ECNM representatives collaborated closely with their U.S. colleagues, various patient organizations, and other scientific networks. Finally, ECNM members have started several collaborations with industrial partners, leading to the preclinical development and clinical testing of KIT-targeting drugs in systemic mastocytosis, and some of these drugs received licensing approval in recent years. All these networking activities and collaborations have strengthened the ECNM and supported our efforts to increase awareness of MC disorders and to improve diagnosis, prognostication, and therapy in patients.

Guiding Clinical Prescription of Topical Extemporaneous Formulations of Sodium Cromoglycate Based on Pharmaceutical Performance

Cromoglycate (SCG) is widely used for allergy processes, and inflammatory states acting as a mast cell membrane stabilizer that inhibits the histamine and mediator release. Currently, SCG topical extemporaneous compounding formulations are prepared in hospitals and community pharmacies, as no industrial fabricated medicines are available in Spain. The stability of these formulations is unknown. Additionally, there are no clear guidelines on which concentration and vehicle are more suitable to enhance permeation across the skin. In this work, the stability of commonly prescribed topical SCG formulations in clinical practice was evaluated. Different vehicles commonly employed by pharmacists daily for formulating topical SCG were investigated (Eucerinum, Acofar Creamgel, and Beeler's base) at different concentrations, ranging from 0.2 to 2%. The stability of topical extemporaneous compounded SCG formulations can be extended for up to three months at room temperature (25 °C). Creamgel 2% formulations significantly improved the topical permeation of SCG across the skin, being 4.5-fold higher than formulations prepared with Beeler's base. The reason attributed to this performance can be related to the lower droplet size formed upon dilution in aqueous media combined with a lower viscosity, which facilitates its application and extensibility on the skin. The higher the SCG concentration in Creamgel formulations, the higher the permeability across both synthetic membranes and pig skin (p-value < 0.05). These preliminary results can be used as a guide to prompt a rational prescription of topical SCG formulations.

Molecular Mechanisms of Neurogenic Inflammation of the Skin

The skin, including the hypodermis, is the largest body organ and is in constant contact with the environment. Neurogenic inflammation is the result of the activity of nerve endings and mediators (neuropeptides secreted by nerve endings in the development of the inflammatory reaction in the skin), as well as interactions with other cells such as keratinocytes, Langerhans cells, endothelial cells and mast cells. The activation of TRPV-ion channels results in an increase in calcitonin gene-related peptide (CGRP) and substance P, induces the release of other pro-inflammatory mediators and contributes to the maintenance of cutaneous neurogenic inflammation (CNI) in diseases such as psoriasis, atopic dermatitis, prurigo and rosacea. Immune cells present in the skin (mononuclear cells, dendritic cells and mast cells) also express TRPV1, and their activation directly affects their function. The activation of TRPV1 channels mediates communication between sensory nerve endings and skin immune cells, increasing the release of inflammatory mediators (cytokines and neuropeptides). Understanding the molecular mechanisms underlying the generation, activation and modulation of neuropeptide and neurotransmitter receptors in cutaneous cells can aid in the development of effective treatments for inflammatory skin disorders.

Tryptase in type I hypersensitivity

Tryptase is currently the main mast cell biomarker available in medical practice. Tryptase determination is a quantitative test performed in serum or plasma for the diagnosis, stratification, and follow-up of mast cell-related conditions. The continuous secretion of monomeric α and β protryptases forms the baseline tryptase level. Transient, activation-induced release of tryptase is known as acute tryptase. Because mast cells are tissue-resident cells, the detection of an acute tryptase release in the bloodstream is protracted, with a delay of 15 to 20 minutes after the onset of symptoms and a peak at approximately 1 hour. Constitutive release of tryptase is a marker of mast cell number and activity status, whereas transient release of mature tryptase is a marker of mast cell degranulation. Although consensual as a concept, the application of this statement in clinical practice has only been clarified since 2020. For baseline tryptase to be used as a biomarker, reference values need to be established. In contrast, defining a transient increase using acute tryptase can only be achieved as a function of the baseline status.

How to evaluate the patient with a suspected mast cell disorder and how/when to manage symptoms

Mast cell disorders include mastocytosis and mast cell activation syndromes. Mastocytosis is a rare clonal disorder of the mast cell, driven by KIT D816V mutation in most cases. Mastocytosis is diagnosed and classified according to World Health Organization criteria. Mast cell activation syndromes encompass a diverse group of disorders and may have clonal or nonclonal etiologies. Hematologists may be consulted to assist in the diagnostic workup and/or management of mast cell disorders. A consult to the hematologist for mast cell disorders may provoke anxiety due to the rare nature of these diseases and the management of nonhematologic mast cell activation symptoms. This article presents recommendations on how to approach the diagnosis and management of patients referred for common clinical scenarios.