​

Lawrence B. Afrin, M.D.

Senior Consultant in Hematology/Oncology

Department of Mast Cell Studies

AIM Center for Personalized Medicine

Purchase, New York, USA

Entire presentation copyright © 2024 by Lawrence B. Afrin, M.D. All rights reserved.

Renegade Research

Diagnosis of�Mast Cell Activation Syndrome

Clinicians’ Roundtable

June 22, 2024

Learning Objectives & Disclaimers

• Learning Objectives
• Understand details of:
• General approach for diagnosing mast cell activation syndrome (MCAS)
• Challenges in diagnosing MCAS
• Relationship between MCAS and hereditary alpha-tryptasemia
• Conflicts of Interest
• None
• Note that there are not yet any FDA-approved treatments for MCAS, and not even (yet) any “well-designed, non-randomized clinical trials,” let alone (yet) any “high-quality randomized controlled clinical trials” (there just hasn’t been time yet for such trials!), so by definition, all treatment options discussed in this presentation are ACCME Level Of Evidence (LOE) “C” (“consensus viewpoint or expert opinion”).

​

Outline

• Diagnosing MCAS
• Diagnostic Criteria
• General Approach
• Mast Cell Mediator Levels
• Autoantibodies
• Tissue Biopsies
• Hereditary Alpha-Tryptasemia
• Differential Diagnostic Considerations
• See separate MCAS: Current Concepts introductory lecture

Introduction: What is MCAS?

• Mast cell activation syndrome (MCAS) appears to be…
• …a confoundingly, extraordinarily heterogeneous chronic multisystem polymorbidity of general themes of:
• Inflammation (the “universal constant” of the disease)
• ± allergic-type phenomena (e.g., allergy, urticaria, angioedema, anaphylaxis)
• ± aberrant growth/development in potentially any tissue (e.g., cysts, fibrosis, aneurysms, ?weak connective tissue (Ehlers-Danlos syndrome), ?neurodevelopmental disorders (autism))
• …the far dominant “bulk” of the iceberg of mast cell activation disease (MCAD)
• Prevalence estimates range from rare to 20% of the general population

Haenisch B, et al. Immunol 2012;137:197-205.

Molderings GJ, et al. PLoS One 2013;8(9):e76241

Introduction: What is MCAS?

• Mast cell activation syndrome (MCAS) may be…
• …a primary disease (in most MCAS pts?) rooted in
• Mast cell regulatory gene mutations (almost always acquired)
• Perhaps even deeper (inheritable?) epigenetic roots?
• Autoimmunity
• Other mechanisms?
• …a secondary disease rooted in
• Chronic inflammatory disease driven or not driven by MCAS
• Malignancy (especially hematologic)
• Toxic exposures (overt or not)
• Etc. etc. etc.

Molderings GJ. The genetic basis of mast cell activation disease – looking through a glass darkly. Crit Rev Oncol Hematol 2015;93:75-89 [PMID: 25305106 DOI: 10.1016/j.critrevonc.2014.09.001].

Introduction: What is MCAS?

• Mast cell activation syndrome (MCAS) may be…
• Presently identifiable as clonal
• This is rare
• Identified by either or both of…
• PCR testing showing KIT codon 816 mutations (usually D816V)
• Flow cytometry showing CD117 co-expression on a cell surface with CD25 and/or CD2
• Not presently identifiable as clonal
• The vast majority of MCAS
• But likely clonal anyway in most cases?
• Thus, beware assertions, without proof, of “non-clonal” MCAS

Molderings GJ. The genetic basis of mast cell activation disease – looking through a glass darkly. Crit Rev Oncol Hematol 2015;93:75-89 [PMID: 25305106 DOI: 10.1016/j.critrevonc.2014.09.001].

Diagnosing MCAS: Proposed Criteria

• No true consensus yet
• Too early?
• The “consensus-1” criteria proposal
• Self-described as “consensus” (?) criteria
• Problematic in many respects
• More likely to exclude patients who truly have MCAS?
• The “consensus-2” criteria proposal
• More likely to include patients who truly have MCAS?

Diagnosing MCAS: Criteria

• The “consensus-1” criteria proposal
• Originally published in 2012 by Valent et al. as a “consensus”
• A tweaking of the original Akin et al. 2010 proposal
• Republished in 2019 and since with no significant changes
• Must have two or more (i.e., multisystem presentation) of:
• Flushing, pruritus, urticaria, angioedema, nasal congestion, nasal pruritus, wheezing, throat swelling, headache, hypotension, diarrhea
• More recent iterations of “consensus-1” have no longer considered neurologic issues and have emphasized having anaphylaxis, i.e., if you haven’t had anaphylaxis, you almost certainly don’t have MCAS
• But consensus-2 literature* shows only 7% of MCAS patients have ever had anaphylaxis or even anaphylactoid-type events
• Increase in serum total tryptase by at least 20% above an asymptomatic baseline plus 2 ng/ml during or within 4 hours after a symptomatic period
• Response of clinical symptoms to histamine receptor blockers or “MC-targeting” agents, e.g., cromolyn

Akin C et al. Mast cell activation syndrome: proposed diagnostic criteria. J Allergy Clin Immunol 2010; 126:1099-1104.e4.

Valent P et al. Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal. Int Arch Allergy Immunol 2012 Jan;157:215-225.

Valent P et al. Proposed diagnostic algorithm for patients with suspected mast cell activation syndrome. JACI In Pract 2019;7(4):1125-33.e1

*Afrin LB, Self S, Menk J, Lazarchick J. Am J Med Sci 2017;353(3):207-215.

​

“Consensus-1” Criteria Issues

• Problem: Methods by which “consensus” was obtained
• Single, short, closed meeting
• Problem: Requirement for presentation of one or more listed MCAS-driven symptoms, but few symptoms listed
• Problem: Requires showing a rise in tryptase (within 4 hours of onset of flare) of 20% + 2 ng/ml over asymptomatic baseline
• Does an “asymptomatic baseline” exist in an MCAS patient?
• Having a blood sample for a tryptase level drawn within 4h of flare
• Allowing levels well within normal range to signify disease
• No published data whether this distinguishes nl./abnl. fluctuation in the general MCAS population despite repeated assertions otherwise
• Problem: Requires response to MC-targeted therapy
• Assumes all patients with this very heterogeneous disease will respond
• After how many empiric treatment failures is the diagnosis ruled out?
• Is treating prior to diagnosis appropriate?

Valent P et al. Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal. Int Arch Allergy Immunol 2012 Jan;157:215-225.

Akin C et al. Mast cell activation syndrome: proposed diagnostic criteria. J Allergy Clin Immunol 2010; 126:1099-1104.e4.

Valent P et al. Why the 20% + 2 tryptase formula is a diagnostic gold standard for severe mast cell activation and mast cell activation syndrome. Int Arch Allergy Immunol 2019;180(1):44-51, doi: 10.1159/000501079.

Diagnosing MCAS: Criteria

• “Consensus-2” proposal:
• Major criterion:
• Constellation of clinical complaints attributable to pathologically increased MC activity (MC mediator release syndrome)
• Minor criteria:
• Multifocal or disseminated infiltrates of MCs in marrow and/or extracutaneous organ(s) (e.g., gastrointestinal or genitourinary tract; ≥20 MCs/high power field)
• Abnormal spindle-shaped morphology in >25% of MCs in marrow or other extracutaneous organ(s)
• Abnormal MC expression of CD2 and/or CD25 (i.e., co-expression of CD117/CD25 or CD117/CD2)
• MC genetic changes (e.g., activating KIT codon 419, 509, or 560 mutations) shown to increase MC activity
• Evidence (typically from body fluids such as whole blood, serum, plasma, or urine) of above-normal levels of MC mediators including: tryptase, histamine or its metabolites (e.g., N-methylhistamine), heparin, chromogranin A (note potential confounders of cardiac/renal/hepatic failure, neuroendocrine tumors, chronic atrophic gastritis, or recent proton pump inhibitor use), other relatively MC-specific mediators (e.g., eicosanoids including prostaglandin (PG) D₂, its metabolite 11-β-PGF_2α, or leukotriene E4)
• Symptomatic response to inhibitors of MC activation or MC mediator production or action
• Diagnosis made upon fulfillment of the major criterion + ≥ 1 minor criterion…
• …and, of course, no other evident diagnosis which better accounts for the full range and duration of all the symptoms and findings in the history, exam, and labs

Afrin LB et al., Diagnosis 2020 Apr 22;8(2):137-152. doi: 10.1515/dx-2020-0005, updated from Molderings GJ et al. F1000Res 2017 Oct 26;6:1889. doi: 10.12688/f1000research.12730.1, updated from Afrin LB, et al. Ann Med 2016;48(3):190-201, updated from Molderings G, et al. J Hematol Oncol 2011;4:10.

​

Same as WHO

Same as WHO

Expanded

Expanded

New

Added

Expanded

MCAS: Recognition

• Traditional diagnostic paradigm (symptom A + exam finding B + test result C ⇒ suspect diagnosis D) doesn’t work for MCAS
• Instead, need to recognize either of two “metapatterns”:
• Multiple chr. inflamm. ills often unsatisfactorily responsive to R_x
• Definitively diagnosed ailment which doesn’t explain all of the symptoms, findings, and results
• Validated screening tools available

Molderings G et al. Die systemische Mastzellerkrankung mit gastrointestinal betonter Symptomatik - eine Checkliste als Diagnoseinstrument. Deutsche medizinische Wochenschrift 2006 Sep 22; 131(38):2095-100.

Alfter K et al. New aspects of liver abnormalities as part of the systemic mast cell activation syndrome. Liver International 2010;29(2):181-186.

Weinstock LB et al. Mast Cell Activation Syndrome: A Primer for the Gastroenterologist. Dig Dis Sci 2021 Apr;66(4):965-982.

MCAS: Diagnosis

• Best diagnostic aids:
• Most physicians’ best friend: a complete history and exam
• Faith in Occam’s Razor: which scenario is more likely?�
• Multiple diagnoses/problems all independent of each other��vs.�
• One diagnosis that’s biologically capable of causing most or all of the findings (i.e., the simplest solution, even if it’s not the most immediately obvious solution)

MCAS�Diagnostic�Work-Up:�2024

Afrin LB, Molderings GJ. A concise, practical guide to diagnostic assessment for mast cell activation disease. World J Hematol 2014 Mar;3(1):1-17.

Diagnosing MCAS: General Approach

• The hardest part of diagnosing MCAS: Taking the time to appreciate the full range of problems in the patient
• Take/re-take a full history
• Take a full review of systems
• Perform a full physical examination

Diagnosing MCAS: General Approach

• The hardest part of diagnosing MCAS: Taking the time to appreciate the full range of problems in the patient
• Take/re-take a life-long history
• Symptoms of MCAS usually date back at least to adolescence (puberty, especially in girls, often sparks a sustained escalation of symptoms), not uncommonly to childhood or even infancy.
• Consider taking mother’s history of pregnancy with patient, too
• Symptoms are often chronic/recurrent, episodic/intermittent, and/or waxing/waning
• Flares may happen at any time but often are in reaction to a physical or chemical exposure or to an event
• Flares usually are temporary (minutes to weeks/months) but sometimes are permanent (the “steps” on the “step-wise” natural history of escalation of the disease)

Diagnosing MCAS: General Approach

• The hardest part of diagnosing MCAS: Taking the time to appreciate the full range of problems in the patient
• Take/re-take a life-long history
• Block out the time needed to take a long history. And note this is NOT a “chief complaint”-directed history. These patients typically have a zillion complaints, frustrating the doctor who wants there to be a chief complaint, so that the history and exam can then be focused and abbreviated. Instead, try to direct the patient chronologically, so you can appreciate how the disease likely has shaped the patient’s entire life (inflammation, allergy, aberrancies in growth/development)…
• …but remember it’s hard to remember chronologies and “ancient events,” and accept that patients frequently will have “aha!” moments and go back and fill in more events on the timeline.
• Stress (physical or psychological/emotional) can escalate (often permanently) the baseline misbehavior of the dysfunctional mast cells in MCAS, and we all suffer stressors at various times. Ergo, the social history is important.
• Capture major life events: puberty, college, marriage, pregnancies, deliveries, employment and family stressors (weddings, deaths, abuse), relocations
• Physical stressors which can escalate MCAS include surgery, trauma, puberty, major immunologic events (e.g., infections, vaccinations, novel antigenic exposures (e.g., relocations, travel)), pregnancy/childbirth, menarche/menopause.
• When the medical problems fairly suddenly significantly worsen, search for physical or psychological stressors, or new exposures (food, medications, materials, environmental factors) in the few days to few months prior to the exacerbation.

Diagnosing MCAS: General Approach

• The hardest part of diagnosing MCAS: Taking the time to appreciate the full range of problems in the patient
• Take/re-take a life-long history
• There’s a strong familial propensity for MCAS (75% chance a 1^st degree relative will have it, 50% chance of each child of an MCAS-afflicted couple having it).
• Take a full family history and watch how the issues potentially consistent with MCAS emerge (though often quite different from one affected family member to the next).
• The medication/allergy history is important and not uncommonly already demonstrates excipient reactivity (“I can’t tolerate Benadryl – but I do fine when it’s given IV”).
• Take a full review of systems
• There is no system – including the immune system – which is immune to potentially being affected.
• Most MCAS patients learned early that complaining about their symptoms was unproductive – even counterproductive – diagnostically and therapeutically
• They stop volunteering their symptoms; asking about them is important!
• They accept their symptoms as “my normal” and “learn to live with them”

Molderings GJ, et al. PLoS One 2013;8(9):e76241

Characterization of MCAS

Afrin LB, Self S, Menk J, Lazarchick J. Am J Med Sci 2017;353(3):207-215.

Characterization of MCAS

Afrin LB, Self S, Menk J, Lazarchick J. Am J Med Sci 2017;353(3):207-215.

Diagnosing MCAS: ROS

• Fevers (much more often subjective than objective)
• Flushing
• Chills/rigors (uncommonly) or just feeling cold much of the time (much more commonly)
• Fatigue (often to the point of exhaustion), malaise
• Headaches (of any type)
• Diffusely migratory aching/pain
• Diffusely migratory pruritus
• Unprovoked soaking sweats (often nocturnal)
• Unprovoked fluctuations in weight and/or appetite
• Irritation of the eyes
• Acute brief inability to focus vision
• Tinnitus
• Hearing impairment/congestion

• Epistaxis
• Easy bleeding/bruising
• Sinonasal congestion, coryza, post-nasal drip
• Irritation of the nose (including intranasal sores)
• Irritation of the mouth (typically mouth sores)
• Irritation of the throat (often chronic/frequent throat-clearing)
• Dysphagia (usually proximal, occasionally globus)
• Dyspnea (most often “at times I suddenly just can’t catch a deep breath,” less commonly with mild wheezing)
• Palpitations
• Chest discomfort/pain (usually non-anginal)

• Gastroesophageal reflux (often PPI-refractory)
• Nausea, vomiting
• Diarrhea (usually alternating with constipation)
• Diffusely migratory abdominal discomfort/pain including (usually post-prandial) bloating
• Urinary frequency or polyuria or hesitancy or retention, occ. stones
• Dysuria (often culture-negative)
• Diffusely migratory edema
• Diffusely migratory or intermittently global weakness
• Diffusely migratory tingling/numbness (typically about the distal extremities)
• Seizures and/or pseudoseizures
• Diffusely migratory adenopathy and adenitis

• Orthostatic and non-orthostatic presyncope (common)
• Syncope (rare)
• BP and pulse lability
• Cognitive dysfunction (particularly memory, concentration, and word-finding)
• Hair loss (less commonly, undesirable hair growth)
• Deterioration of dentition despite good attention to dental hygiene
• Brittle and/or ridged nails
• Appearing/disappearing tiny white spots on the nails
• Diffusely migratory rashes (typically patchy macular erythema)
• Hives
• Dyshydrotic eczema

Diagnosing MCAS: ROS

• Insomnia and/or hypersomnia and other parasomnias
• Joint hypermobility
• Connective tissue weakness

• Unusually vigorous insect bite reactions
• Slow/poor healing, tendency to form scars and keloids

Diagnosing MCAS: ROS

Diagnosing MCAS: General Approach

• The hardest part of diagnosing MCAS: Taking the time to appreciate the full range of problems in the patient
• Perform a full physical examination
• There is no tissue which is immune to potentially being affected by MCAS.
• Mast cells reside in every vascularized tissue but are present in greatest numbers at environmental interfaces and abutting all vessels (blood and lymph) and all neurons (peripheral and central)
• Vitals (note frequent discrepancy between high check-in pulse and lower pulse measured at exam after taking a long history, reflecting dysautonomic exercise intolerance in simply walking from waiting room to exam room), skin, hair, EENT (including teeth), CV, lungs, abdomen, GU, musculoskeletal, neurologic, psychiatric

Characterization of MCAS

Afrin LB, Self S, Menk J, Lazarchick J. Am J Med Sci 2017;353(3):207-215.

Diagnosing MCAS: General Approach

• The hardest part of diagnosing MCAS:
• Taking the time to appreciate the full range of problems in the patient
• The second hardest part of diagnosing MCAS:
• Accepting that there really is a disease which you weren’t taught in training but which really can account for most or all of what has gone on in the patient.
• The third hardest part of diagnosing MCAS:
• Not rushing to a diagnosis of MCAS; taking the time to think about (and, as appropriate, test for) other diseases which might better account for the full range and duration of all the symptoms and findings in the case.
• The least difficult part of diagnosing MCAS, once the first three hardest parts have been attended to:
• Finding laboratory evidence of the disease
• It’s the least difficult part, but still decidedly non-trivial

Diagnosing MCAS: General Approach

• Laboratory evidence
• Strongly consider seeking at least two points of laboratory evidence
• Any test can yield an abnormal result once by chance or error
• MCAS is a life-changing (usually not life-shortening, but nevertheless life-changing) diagnosis
• The patient diagnosed with MCAS is placed on a therapeutic path for the rest of his/her life he/she would never be on if it were not for the diagnosis
• Family implications
• Types of laboratory evidence:
• Elevated levels of mediators relatively specific to the mast cell
• The same mediator repeatedly elevated
• Different mediators elevated at the same or different times
• Increased numbers of mast cells in tissues…
• …but not to the level, or with the histologic or morphologic aberrancies, seen in mastocytosis.

Afrin LB, et al. Often seen, rarely recognized: mast cell activation disease – a guide to diagnosis and therapeutic options. Ann Med 2016;48(3):190-201.

Diagnosing MCAS: General Approach

• Laboratory evidence
• Mediator testing is challenging
• Many mediators are highly thermolabile and/or have very short half-lives.
• Most mediator testing is “send-out,” increasing the number of links in the chain of handling and thus the potential for mishandling.
• Avoid (if possible, and sometimes it’s not) potential confounders if possible (PPIs x 3 weeks, NSAIDs/salicylates and other COX1/2 inhibitors (many “anti-inflammatory” “supplements”!) and leukotriene synthesis inhibitors (e.g., zileuton) x 1 week, supraphysiologic doses of vitamins C, D, and E x 1 week).
• Histamine- and leukotriene-receptor blockers, cromolyn, benzos, and cannabinoids are not known to be confounders.
• Mediator testing not uncommonly yields negative results even in spite of flagrant symptoms.
• “Debug” what (if anything) went wrong, and try again (preferably when the patient is at a significantly symptomatic point, though plenty of MCAS patients have elevated mediator levels even when doing “relatively well”).
• The vast majority of patients who behave like they have MCAS indeed have detectable elevations in at least one of the commonly tested mediators within three rounds of blood/urine testing.

Afrin LB, et al. Often seen, rarely recognized: mast cell activation disease – a guide to diagnosis and therapeutic options. Ann Med 2016;48(3):190-201.

MCAS: Diagnostic Lab Issues

• Great thermolability of many mast cell mediators
• Half-lives at room temp. or higher as short as 30 seconds
• Heparin: 30-60 sec.
• Prostaglandin D2: 1-30 min.
• 2,3-dinor-11-beta-prostaglandin-F2-alpha half-life: 1-30 min.
• Histamine in vivo: ~1-2 minutes (sep. plasma: 48 hrs.)
• N-methylhistamine: ~1-2 hrs.
• Tryptase in vivo: 6-8 min. (sep. serum: ~4 days)
• Continuous chilling ESSENTIAL!!!
• Collection into pre-chilled tubes/containers
• Immediate placement of specimens on ice
• Refrigerated centrifugation ESSENTIAL!!!
• Careful packing for chilled transport to reference labs ESSENTIAL!!!

​

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Zenker N, Afrin LB. Utilities of various mast cell mediators in diagnosing mast cell activation syndrome. Blood 2015;126:5174.

MCAS: Diagnostic Lab Issues

• Mast cell mediator thermolability: heparin

Zenker N, Afrin LB. Utilities of various mast cell mediators in diagnosing mast cell activation syndrome. Blood 2015;126:5174.

Diagnosing MCAS: General Approach

• Laboratory evidence
• “Plan B” (if 2-3 rounds of properly handled blood/urine mediator testing yield nothing despite an H&P suggestive of MCAS): tissue biopsies (usually GI, sometimes GU, preferably just re-staining old biopsies rather than obtaining new ones)
• Even if clearly increased mast cells are found in one or more biopsies (old or new), it’s not called a mast cell activation syndrome for nothing, and thus it still would be advantageous to find at least some clear evidence of activation (i.e., at least one elevated mediator level) to complement the biopsy findings
• The patient likely will need to be convincing many other doctors who know little to nothing about MCAS as to the accuracy and significance of the diagnosis for the rest of the patient’s life. Making a solid case diagnostically as early as possible likely will “smooth the way” for future treatment.

Afrin LB, et al. Often seen, rarely recognized: mast cell activation disease – a guide to diagnosis and therapeutic options. Ann Med 2016;48(3):190-201.

Diagnosing MCAS: General Approach

• Typical panel
• CBCD
• CMP, magnesium
• PT/PTT (if history of thromboembolism (not clearly provoked) or easy bleeding/bruising, and not on confounding medication)
• Consider checking anti-phospholipid antibodies if PT or PTT abnormal
• Anti-cardiolipin antibody profile, beta-2-glycoprotein-1 antibody profile, anti-phosphatidylserine and –prothrombin antibody profiles, anti-phosphatidylethanolamine antibody profile, anti-annexin V antibody profile, lupus anticoagulant
• Also consider other testing for other coagulopathies if PT or PTT abnormal
• e.g., mixing studies, von Willebrand disease profile
• Chilled serum tryptase and chromogranin A
• Chilled plasma prostaglandin D2, histamine, heparin
• Chilled random and 24-hour urinary PGD2, [2,3-dinor-]11-beta-PGF2-alpha, N-methylhistamine, leukotriene E4
• Anti-IgE antibodies
• Anti-IgE-receptor antibodies (a.k.a. “chronic urticaria index,” “histamine release assay,” “basophil activation assay”)

Afrin LB, et al. Often seen, rarely recognized: mast cell activation disease – a guide to diagnosis and therapeutic options. Ann Med 2016;48(3):190-201.

Diagnosing MCAS: Mediator Levels

• Serum tryptase
• Highly (but not perfectly) specific to mast cells
• 25% of all protein produced by mast cells is tryptase
• A little bit is made in basophils, too.
• It’s a proteinase, but….40 years since its discovery, its specific principal function remains unclear
• Complex biology, with many isoforms
• Originally described (1987) as a marker of mast cell activation in systemic mastocytosis…
• …but now appreciated to far better reflect the total body mast cell load rather than the total body mast cell activation state
• Thus, tryptase is usually significantly elevated (>20 ng/ml, ~2x ULN) in mastocytosis, but elevated little (<20 ng/ml) to none (most commonly none) in MCAS

Afrin LB, Self S, Menk J, Lazarchick J. Characterization of mast cell activation syndrome. Am J Med Sci 2017;353(3):207-215.

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Diagnosing MCAS: Mediator Levels

• Serum tryptase
• Thermolabile
• Relatively short half-life in vivo (~6-8 minutes)
• Longer half-life in separated serum (~4 days)
• Since it’s hard to know how quickly serum will be separated (especially if it’s a busy point in time for the accessioning lab), and since there is some thermolability to it, and since so many of the other specimens are being kept chilled (due to far greater thermolability), I conservatively ask for tryptase, too, to be drawn into a pre-chilled tube and kept chilled throughout all phases of handling (i.e., consistency in handling of all the specimens should decrease risk for mishandling).

​

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Diagnosing MCAS: Mediator Levels

• Serum tryptase
• Recently described: familial hypertryptasemia (a.k.a. hereditary alpha-tryptasemia (HAT or HαT))
• Autosominal dominant
• One or more (sometimes many more) extra copies of the TPSAB1 (α-tryptase) gene
• In 6% of the general population
• Phenotype is variable and includes some classic MCA phenomena (flushing, venom reactions), EDS-like connective tissue issues, and “functional” GI disorders
• Not clear if the (typically only slightly) elevated tryptase is contributing to the phenotype or is just a bystander/”red herring”
• Not clear if familial hypertryptasemia is just one specific variant of MCAS or a different entity, without MC activation

Sabato et al. Familial hypertryptasemia with associated mast cell activation syndrome. J Allergy Clin Immunol 2014 Dec;134(6):1448-1450.e3.

Lyons et al. Elevated basal serum tryptase identifies a multisystem disorder associated with increased TPSAB1 copy number. Nat Genet 2016 Dec;48(12):1564-1569.

Hereditary Alpha-Tryptasemia

• It’s now understood that about 6-8% of the general population have one or more extra copies of the TPSAB1 gene for alpha-tryptase, defining cases of “hereditary alpha-tryptasemia” (HAT) in which tryptase is constitutively over-expressed and therefore in which elevated levels of tryptase cannot be taken to necessarily be markers of mast cell activation. (HAT is often found in MCAS patients, but also note about 6-9% of HAT patients are asymptomatic, so constitutive tryptase overexpression clearly does not define or cause a syndrome of chronic inappropriate mast cell activation.)
• Therefore, patients suspected of having MCAS in whom the only laboratory evidence found thus far has been one or more mildly elevated tryptase levels now also require TPSAB1 redundancy testing (currently clinically available only at Gene by Gene in Houston, Texas), and if this is positive (defining HAT), the elevated tryptase levels cannot be taken as evidence of MCAS and other laboratory evidence of MCAS should be pursued if possible.

Diagnosing MCAS: Mediator Levels

• Serum chromogranin A (CgA)
• Thermostable, but…
• …since so many of the other specimens are being kept chilled, I conservatively ask for CgA, too, to be drawn into a pre-chilled tube and kept chilled throughout all phases of handling (i.e., consistency in handling of all the specimens should decrease risk for mishandling)
• Known to be produced by the mast cell, but the least mast-cell-specific of the mediators checked in an MCAS work-up.
• Several potential confounders
• Heart or renal or hepatic failure
• Recent (last three weeks) proton pump inhibitor use
• PPIs typically increase CgA to ~2-5x ULN
• Neuroendocrine tumors (NETs)
• Note NETs are rare, the H&P usually argues against NETs, and CgA-producing NETs (i.e., the majority of NETs) usually produce CgA levels > 10x ULN
• CgA is normal in ~2/3 of MCAS patients; in the rest, it’s usually < 10x ULN but occasionally is higher, requiring more careful attention to considering/ruling out NETs

​

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Diagnosing MCAS: Mediator Levels

• Plasma prostaglandin D2 (PGD2)
• Detectable levels are fairly specific to mast cell activation
• A number of other cells make it – but ~3 orders of magnitude less than the mast cell, so if a PGD2 level is detectable, it’s virtually certain it’s coming from activated mast cells
• Thermolabile (half-life ~1-30 min. in various studies)
• Unless immediately plasma-separated and assayed, specimen must be kept continuously chilled through all phases of handling (including centrifugation and shipment)
• Virtually always a send-out to a distant reference lab (most commonly Inter-Science Institute in Inglewood, CA)
• Anything impeding eicosanoid/PG production can be a confounder
• COX1/COX2 inhibitors
• NSAIDs (incl. salicylates) – check prescription and OTC meds (& prn’s!)
• Note MANY foods and household and personal care products have salicylates high up on their ingredient lists (https://aimcenterpm.com/salicylate-sensitivity/)
• Many “supplements” (e.g., ashwagandha, turmeric, green tea, frankincense, resveratrol, quercetin and other flavonoids, garlic, etc. etc. etc. etc.)

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Diagnosing MCAS: Mediator Levels

• Plasma histamine
• No clear advantage to plasma vs. serum vs. whole-blood
• However, a whole blood sample includes (some) basophils and mast cells (containing some histamine), so a whole blood histamine level may not reflect released histamine (i.e., histamine from mast cell or basophil activation) as accurately as a plasma or serum histamine level
• Slightly less specific for mast cell activation than tryptase
• More histamine release (than tryptase release) from basophils
• Short half-life in vivo (~1-2 min., may vary based on increased histaminase activity in anaphylaxis)
• Stable in separated plasma at room temperature for 48h, but…
• …since time to plasma separation can be inconsistent, and since there is some thermolability to it, and since so many of the other specimens are being kept chilled (due to far greater thermolability), I conservatively ask for tryptase, too, to be drawn into a pre-chilled tube and kept chilled throughout all phases of handling (i.e., consistency in handling of all the specimens should decrease risk for mishandling).

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Diagnosing MCAS: Mediator Levels

• Plasma heparin
• Large amounts produced/stored in mast cells
• Only other human source: basophils (tiny quantities)
• Highly thermolabile (half-life ~30-60 seconds)
• Decomposes rapidly even at chilled temperatures
• Perhaps the single most sensitive and specific marker of mast cell activation (elevated in ~40-75% of MCAS patients with sufficiently careful testing), but...
• …upper limit of normal is ~0.02-0.05 anti-Factor Xa units/ml and…
• …the lower limit of detection for virtually every commercially available assay in the U.S. is 0.10-0.30.
• Thus, most elevated heparin levels in MCAS patients will be missed with most U.S. testing, but if any heparin level is detected, it’s a strong sign of mast cell activation.
• Vaso-occlusive testing (10 mm Hg above diastolic x 10 min.) may improve sensitivity; this does not cause false positives in healthy pts.

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Afrin LB, Self S, Menk J, Lazarchick J. Characterization of mast cell activation syndrome. Am J Med Sci 2017;353(3):207-215.

Vysniauskaite M et al. Determination of plasma heparin level improves identification of systemic mast cell activation disease. PLoS One 2015 Apr 24;10(4):e0124912.

Diagnosing MCAS: Mediator Levels

• Urinary prostaglandin D2
• 24-hour and/or random sample
• Continuous chilling from collection through assay
• Especially challenging to collect a chilled 24-hour urine in the inpatient environment
• As with plasma PGD2, must watch out for confounders
• Urinary 2,3-dinor-11-beta-prostaglandin-F2-alpha
• Principal immediate metabolite of PGD2 and PGE2, but though PGE2 is not known to be made in mast cells, “11-beta” is accepted as a marker of mast cell activation
• 24-hour and/or random sample
• Essentially as thermolabile as PGD2; chilling required
• Plasma prostaglandin F2-alpha not specific to MC disease
• More limited data showing PGDM (a.k.a. T-PGDM), available in some countries outside the U.S., may be a useful MC activation marker

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Afrin LB, Self S, Menk J, Lazarchick J.  Characterization of mast cell activation syndrome.  Am J Med Sci 2017;353(3):207-215.

Cho C et al. Prostaglandin D2 metabolites as a biomarker of in vivo mast cell activation in systemic mastocytosis and rheumatoid arthritis. Immun Inflamm Dis 2015 Nov 25;4(1):64-9.

Diagnosing MCAS: Mediator Levels

• Urinary N-methylhistamine (NMH)
• Principal immediate metabolite of histamine
• Longer half-life than histamine (~1-2h), thus preferable to measure compared to histamine if only one or the other can be measured, especially when a sample cannot be collected during or immediately after a flare.
• Normal range different at different ages (0-5, 6-16, 17+)
• 24-hour and/or random sample
• Chilled urine (and centrifugation) is probably better than unchilled

​

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Diagnosing MCAS: Mediator Levels

• Urinary leukotriene E4 (LTE4)
• Stable end-product and regarded as a valid marker of total cysteinyl leukotriene production.
• Also produced by basophils, eosinophils, and macrophages, but regarded as a valid marker of mast cell activation
• 24-hour and/or random sample
• Longer half-life (~7 minutes) than many other MC mediators, but chilling probably still helpful – and since it’s measured out of the same sample which needs to be chilled for accurate measurement of other mediators, this sample also gets chilled by default

​

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Diagnosing MCAS: Mediator Levels

• Any utility to measuring PGE2?
• Mast cells express PGE2 receptors
• Mast cells are not known to produce PGE2
• Can chilling of the 24-hour urine sample be avoided if “preservative” is used in the jug?
• I’m aware that some laboratory reference websites state that preservatives of various sorts can be used in place of chilling, but I’m not aware of any publications – not one – demonstrating that PGD2, 2,3-dinor-11-beta-prostaglandin-F2-alpha, NMH, or LTE4 levels (let alone all four of them) are held stable by any preservative in a room-temperature 24-hour urine collection.

Diagnosing MCAS: Mediator Levels

• What are we really measuring here?
• Mast cells produce/release >1200 mediators (and express >300 receptors, too!)
• What we are measuring in looking for evidence of mast cell activation is a very poor surrogate for the totality of the signaling “chaos” in this disease.
• Therefore, the mediators we’re measuring are not necessarily (and, for most of the disease’s symptoms, if you play the odds, probably aren’t) the mediators producing the symptoms.
• Similarly, there shouldn’t be any surprise that there has not yet been found any correlation between specific symptoms and levels of specific MC mediators or between specific treatments and declines in specific mediator levels.

Afrin L. Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome. In Mast Cells: Phenotypic Features, Biological Functions, and Role in Immunity, Nova Science Publishers, Happauge, NY, 2013, pp. 155-231.

Ibelfaughts H. “Mast Cells” in COPE: Cytokine On-line Pathfinder Encyclopedia, https://www.cells-talk.com

Characterization of MCAS

Afrin LB, Self S, Menk J, Lazarchick J. Am J Med Sci 2017;353(3):207-215.

Characterization of MCAS

Zenker N, Afrin LB. Utilities of Various Mast Cell Mediators in Diagnosing Mast Cell Activation Syndrome. Blood 2015;126(23):5174. DOI: 10.1182/blood.V126.23.5174.5174

Diagnosing MCAS: Autoantibodies

• Anti-IgE antibodies and Anti-IgE-receptor antibodies (“chronic urticaria index,” “basophil activating Abs”) have potential to activate mast cells.
• Likely other MC-activating antibodies exist, but none yet identified.
• MCAS often produces auto- and allo-antibodies
• Often “mimicking” or “pseudo” antibodies
• Titers typically either wax/wane from mildly elevated to undetectable levels, or persist at very high levels – but without symptoms, signs, or other lab findings of the associated disease
• Specific enough to react with a given probe
• Not specific enough to cause the associated autoimmune disease or to reflect a true infection by the associated infectant
• Strongly consider also checking DNA probes, cultures, tissue examinations (e.g., blood smears) for infectants
• Unclear whether anti-IgE/anti-IgE-receptor antibodies in a given MCAS patient are pseudoantibodies or pathogenic
• No “confirmatory” tests available
• No treatment guidelines: at present, it’s solely the physician’s clinical intuition as to whether/when immunosuppressive therapies are warranted.

Diagnosing MCAS: Other Antibody-Related Considerations

• Caution: MCAS commonly drives the humoral immune system to spuriously/randomly produce antibodies not specifically targeted against a detected threat
• Most such antibodies likely undetectable (i.e., no specific probes available for detecting their randomly generated variable regions)
• By chance, some such antibodies will be sufficiently similar to “real, on-target” (allo-/auto-) antibodies to register positive with probes for such “real” antibodies but do not represent the real presence of the infectant or the autoimmune disease (“mimicking antibodies”)
• No tests yet available for distinguishing mimicking from real antibodies, but…

Diagnosing MCAS: Other Antibody-Related Considerations

• …patterns in isotypes and/or titers of mimicking antibodies are often distinct from those of real antibodies
• Two most common patterns of mimicking antibodies
• Most common: titer trend over time waxes/wanes between normal and mildly elevated, never consistent with the severity of symptoms
• Less common: titer trend extremely high (often literally off-the-scale), yet no other evidence (clinical, imaging, etc.) of correspondingly severe disease
• Either pattern: also, isotype pattern and/or isotype switching pattern over time may not be as expected for real antibodies

Mimicking Antibody Patterns in MCAS

Diagnosing MCAS: Other Antibody-Related Considerations

• Barring emergencies (e.g., sepsis, catastrophic anti-phospholipid antibody syndrome, etc.), be very cautious about interpreting a “positive” antibody result (of any sort) in an MCAS patient as diagnostic of the associated disease and initiating treatment unless all three of the following conditions are met:
• The “positive” titer and isotype patterns/trends over time are as expected in the associated disease; consider confirming the “positive” result, too, at a different lab
• The infectious or autoimmune disease associated with the “positive” antibody is clearly clinically present
• Other (non-antibody-based) tests available for confirming the presence of the infectious or autoimmune disease associated with the “positive” antibody are also clearly positive in the patterns expected in true cases of the associated disease; again, consider confirming the “positive” confirmatory test at a different lab

Diagnosing MCAS: Other Antibody-Related Considerations

• Most important guiding principles:
• Trust your clinical “gut intuition” (treat the patient, not the numbers)
• Patients usually get better when given appropriate treatment for the right diagnosis, so the correctness (or completeness) of the diagnosis has to be reconsidered in patients not responding to treatment as expected

Diagnosing MCAS: Biopsies

• Cutaneous mastocytosis
• Most common form: urticaria pigmentosa (UP)
• Uncommonly: telangiectasia macularis eruptiva perstans (TMEP)
• Skin biopsies in an MCAS patient of a rash that doesn’t look like UP/TMEP are unlikely to be helpful
• Typical reading: “urticarial reaction” or “superficial and/or deep lymphocytic (or lymphohistiocytic) infiltration with occasional admixed eosinophils”

Diagnosing MCAS: Biopsies

• Marrow biopsies in MCAD patients
• Especially in a patient whose presentation is more consistent with MCAS than SM, marrow biopsy is very unlikely to reveal the rare disease of systemic mastocytosis (let alone the even rarer subtypes of aggressive SM)
• The far dominant subtype (~70%) known as indolent SM appears to have the same prognosis as MCAS.
• I consider marrow biopsies only in patients with an MCAD phenotype who have a serum tryptase persistently > 20 ng/ml (per WHO criteria for SM) or who were healthy and then had sudden onset of symptoms in middle or older age.
• Bilateral biopsies are advised when looking for SM; a unilateral biopsy will miss this patchy disease about one-sixth of the time.
• May reveal monoclonal MCAS (MMCAS) in 1-2% of pts, but…
• …no difference known presently in prognosis or approach to treatment between MCAS vs. MMCAS.
• The involved cell population is usually well less than 1% of the nucleated cells.

Diagnosing MCAS: Biopsies

• More on marrow biopsies in MCAD patients
• Tests to order:
• Routine histology
• Routine histochemical/ immunohistochemical staining for mast cells (including CD117 at a bare minimum)
• Routine cytogenetics/karyotyping (virtually always normal)
• KIT-D816V mutation analysis by PCR (or, if available, KIT hot spot mutation analysis by next-gen sequencing, or even whole KIT sequencing) – in an MCAS patient, defines MMCAS
• Quantitative real-time PCR (qrt-PCR) testing for KIT-D816V is best, but not widely clinically available yet
• Flow cytometry for cell-surface CD117 co-expression with CD25 and/or CD2 – in an MCAS patient, defines MMCAS
• Most laboratory pathologists (even flow cytometrists) are not yet familiar with this; flow cytometry can only be done on fresh tissue, so plan for this “special” flow cytometry in advance!

Diagnosing MCAS: Biopsies

• More on marrow biopsies in MCAD patients
• What marrow biopsies usually show in SM:
• Abnormal histology:
• Increased numbers of mast cells (more than the usual ~1-2% of the nucleated cell population)
• Dense aggregates (aggregation of mast cells is abnormal) of 15+ mast cells
• Abnormal morphology: Often, spindling of mast cells (mast cells normally are round or ovoid, which is why they are often mistaken on H&E staining for lymphocytes, plasma cells, macrophages, or histiocytes)

Diagnosing MCAS: Biopsies

• More on marrow biopsies in MCAD patients
• What marrow biopsies usually show in MCAS (my experience):
• Most common result: normal cellularity with normal trilineage hematopoiesis, normal karyotype, and no molecular findings (on PCR or flow cytometry) suggestive of MMCAS
• Second most common result: a vaguely/mildly myelodysplastic and/or myeloproliferative picture, mildly increased cellularity, normal karyotype, and no molecular findings (on PCR or flow cytometry) suggestive of MCAS

Diagnosing MCAS: Biopsies

• More on marrow biopsies in MCAD patients
• Be careful of marrow biopsies suggesting MDS or MPN:
• The pathologist usually will specifically comment the picture is insufficient to diagnose myelodysplastic syndrome (MDS) or a myeloproliferative neoplasm (MPN) even if blood count abnormalities and/or marrow histomorphology “consistent with” some extent of dysplasia or myeloproliferation are present.
• Nevertheless, the “dysplastic” or “proliferative” wording in the report sometimes leads to (mis)diagnosis and (mis)treatment (usually ineffective) of “cytogenetically normal MDS” (a category of MDS comprising ~50% of MDS) or “triple-negative MPN” (JAK2/CALR/MPL-mutation-negative MPN).
• As with the presence of specific antibodies in MCAS not necessarily reflecting true autoimmune or infectious disease, don’t diagnose a malignancy based on a “wavering” pathology report unless the patient is clearly behaving as the suspected malignancy is expected to behave.

Diagnosing MCAS: Biopsies

• GI tract biopsies in MCAS patients
• Many MCAS patients already have had GI tract biopsies taken; these biopsies are “low-hanging” diagnostic fruit
• Mast cells CANNOT be recognized as mast cells on routine (H&E) staining; special staining is required
• This is (part of) what German medical student Paul Ehrlich (later) won the 1908 Nobel Prize for figuring out.
• Pathologists have no reason by default to apply special staining for mast cells to any biopsy; they must be given a reason, and few proceduralists (gastroenterologists, uro/gynecologists, surgeons, etc.) have mast cell disease of any sort in their differential diagnosis.
• In the U.S., most pathologists have financial disincentive to re-visit biopsies they originally read more than two years ago.
• Biopsies older than two years may need to be sent to another pathologist for (properly compensated) “consultative” staining and reading.

Characterization of MCAS

Afrin LB. Polycythemia from mast cell activation syndrome: lessons learned. Am J Med Sci 2011 Jul;342(1):44-9. DOI: 10.1097/MAJ.0b013e31821d41dd.

Characterization of MCAS

Weinstock LB, et al. Mast Cell Activation Syndrome: A Primer for the Gastroenterologist. Dig Dis Sci 2021 Apr;66(4):965-982. DOI: 10.1007/s10620-020-06264-9.

Diagnosing MCAS: Biopsies

• GI tract biopsies in MCAS patients
• Esophageal biopsies in MCAS patients occasionally show eosinophilic esophagitis (EoE, quite possibly consequential to MCAS) but rarely show increased MCs.
• Duodenal and terminal ileal biopsies are most fruitful, but every other segment not uncommonly shows increased MCs, too.
• I therefore request of the gastroenterologist or surgeon, when necessary, bidirectional endoscopy with at least one biopsy of each segment, including biopsies of any lesions seen (usually not seen, but when seen, most commonly just macroscopically appearing as patches of inflammation) as well as blind/random biopsies of macroscopically normal tissues.
• Optional (and rarely done): also submitting fresh (not fixed) biopsies for flow cytometry for CD117 co-expression with CD25 and/or CD2

Diagnosing MCAS: Biopsies

• GI tract biopsies in MCAS patients
• I also request the pathologist perform MC-specific staining (CD117 at a bare minimum, plus other stains as the pathologist may prefer) and report, at a minimum, the count, for each stain on each biopsy, of the maximum number of MCs seen in any one high-power field (40x objective x 10x ocular = 400x total magnification). The pathologist is welcome to comment, if he desires, whether any of the counts seem abnormal (increased).
• For particularly high counts (e.g., >~50-60/hpf), I consider asking the pathologist (if he hasn’t already done it) to send a representative slide for KIT-D816V mutation analysis by PCR.
• Counts standardized per mm² are best but usually not reported/reportable

Diagnosing MCAS: Biopsies

• GI tract biopsies in MCAS patients
• Systemic mastocytosis in the GI tract usually shows at least 100 MCs/hpf and most commonly >200 MCs/hpf
• MCs in SM almost always are aggregated (abnormal!) and often are spindled (abnormal!)
• MCAS in the GI tract often shows “increased” MCs, but they are not aggregated and are a normal round or ovoid shape (distinctive from interstitial cells of Cajal (ICCs), the only other bright-CD117-staining cells, but ICCs are spindled)

Diagnosing MCAS: Biopsies

• GI tract biopsies in MCAS patients
• Note CD117 is fairly well accepted at this point as the best “special stain” for MCs.
• Older histochemical stains (tryptase, Giemsa, toluidine blue, Alcian blue) target granules or the mediators therein, but in a disease of chronic MC activation (i.e., chronic MC degranulation), granule-targeting stains may reveal fewer MCs than are actually present
• CD117 immunohistochemical stain targets CD117, the extracellular domain of KIT, the transmembrane tyrosine kinase which is the dominant MC regulatory element and which studs the surface of the MC an order of magnitude more brightly than any other cell, regardless of whether the cell is granulated or degranulated.

Diagnosing MCAS: Biopsies

• GI tract biopsies in MCAS patients
• “How many is too many?” What constitutes an “increased” number of mast cells in the GI tract?
• No definitive, “gold standard” study
• All available studies are significantly flawed, most with respect to “healthy controls” (often those undergoing screening colonoscopies) whose true health has been vetted little, if any.
• “Best” (i.e., least worst) available study (cited, in my experience, by the great majority of pathologists, when pressed, as the arbiter on this matter) is Jakate et al., Arch Pathol Lab Med 2006, demonstrating a mean mast cell count of 13/hpf with a standard deviation of 3, suggesting >20/hpf (i.e., more than two standard deviations above the mean) as abnormal.
• Better data desperately needed! (Who’s going to be first? Is such a (well-designed, rigorously executed) study even feasible?)

Characterization of MCAS

Weinstock LB, et al. Restless legs syndrome is associated with mast cell activation syndrome. J Clin Sleep Med 2020 Mar 15;16(3):401-408. DOI: 10.5664/jcsm.8216.

Diagnosing MCAS: Biopsies

• GI tract biopsies in MCAS patients
• Might a “depletion index” of one MC-specific mediator or another in MC-containing tissues be helpful toward identifying cases of MCAS?
• As the central issue in MCAS is inappropriate activation (i.e., mediator release) of MCs, and since CD117 is ubiquitously/constantly expressed on MCs, perhaps the difference between CD117-positive MCs and (insert mediator here)-positive MCs in MCAS patients might be significantly/reliably greater than in healthy people

Zienkiewicz T, et al. Evaluation of a tryptase depletion index for better pathologic identification of mast cell activation syndrome. Z Gastroenterol 2023 Mar;61(3):268-274. DOI: 10.1055/a-1833-9226.

Diagnosing MCAS: Biopsies

• GU tract biopsies in MCAS patients
• Biopsies of cervix and endometrium, endometrial implants, resected ovarian cysts, etc. are all fodder (in a patient suspected of having MCAS) for CD117 staining
• “How many is too many?”
• Very limited available data, and expert experience (e.g., T. Theoharides, Nova Southeastern Univ., personal communication), suggest the same >20/hpf threshold as in the GI tract is appropriate for GU tract biopsies, too.
• Other tissues
• “Upper-normal” even more poorly defined
• Tissue-specific literature reviews warranted

Diagnosing MCAS: Other Tests

• Other diseases or classes of diseases which may be appropriate to rule out in selected patients also suspected of having MCAS
• Porphyrias
• Certain malignancies (typically lymphoplasmacytic (e.g., amyloidosis) and neuroendocrine)
• Rheumatologic diseases
• Endocrinologic diseases (e.g., Cushing’s, Addison’s, hyper- or hypo-thyroidism; do not be fooled by trivial degrees of abnormalities on the relevant tests)
• Eosinophilic diseases
• Chronic infectious diseases (esp. in pts with appropriate exposure histories (e.g., ticks, pets, travel, etc.) and treatment-resistant pts)
• Micronutrient deficiencies (possibly primary, but more commonly consequential to MCAS)
• Various types of humoral immunodeficiencies
• “Common variable immunodeficiency”
• Congenital IgA deficiency
• Autoinflammatory syndromes (a.k.a. “periodic fever syndromes”)
• Etc. etc. etc. etc. etc.

After Years of Mystery, The Patient Now Has a New Diagnosis of MCAS.�What Now?

• Prognosis
• Treatment

Diagnosis of MCAS: What’s next?

• Improved diagnostic techniques
• More widely available mediator testing
• Clinically available genomic sequencing of mast cell isolates to distinguish primary from secondary disease and identify mutational patterns correlating with various clinical presentations
• Better identification of autoimmunity-driven MCAS�
• Higher quality diagnostic criteria consensus determinations

Summary

• Diagnosis of MCAS
• Take the time to fully appreciate all the disease can do
• Accept that the disease exists and can do all that it’s done
• Carefully consider the differential diagnosis; Occam’s Razor is a powerful principle, but MCAS does not render one immune to developing any other, non-MCAS-driven disease
• Find the laboratory evidence of disease that has to be there
• The patient may not need to convince you that he/she has MCAS, but he/she will need to be convincing other doctors for decades to come that he/she has this disease these doctors likely don’t know. Lab evidence will help greatly with such convincing.��

Questions?

Questions later?

drafrin@aimcenterpm.com