What is Mast Cell Activation Syndrome (MCAS)? – Dr. Tania Dempsey

Mast cell activation syndrome (MCAS) is increasingly appearing to be the bulk of the iceberg of mast cell activation diseases (MCAD), all of which share the common theme of inappropriate mast cell activation. Mast cells are immune/defense cells found throughout the body, normally sitting quietly in the tissues and just sensing for assaults, whether infectious, environmental or otherwise. When triggered, they can react explosively, producing and releasing into the tissues (and even the circulation) a wide range of potent chemical signals called mediators, each of which has a vast array of effects on other cells and tissues to help the body resist and recover from the assault. We’ve known about some types of MCAD – the tip of the iceberg – for a long time: allergies and other allergic-type problems, and the rare disease of mastocytosis which features not only inappropriate mast cell activation but also excessive (cancerous) mast cell growth. In the last decade, we’ve begun to learn there is a variety of other patterns of inappropriate mast cell activation, causing an array of clinical illnesses we now are collectively terming mast cell activation syndrome (MCAS).

MCAS causes chronic inflammation in multiple organs/tissues/systems, with or without allergic-type problems and sometimes even abnormal growth and development in various tissues, and there can be acute flares (“spells”) of symptoms from time to time as well. Although its variability in clinical presentation can make it difficult to initially recognize MCAS as the underlying/unifying root of the typical patient’s many ills, we are increasingly recognizing MCAS is a common problem. Fortunately, even though MCAS is not presently curable, there are many treatments known to be helpful for controlling the disease, and most patients accurately diagnosed with it can get significantly better even if they have been suffering for decades.

What ARE THE SYMPTOMS OF Mast Cell Activation Syndrome (MCAS)?

Because mast cells are present in virtually every tissue in the body and release mediators which can have a range of effects on other cells, many different symptoms can be seen. There are often acute “spells” of more severe symptoms suffered at irregular intervals in addition to the “baseline” of chronic waxing/waning symptoms. Although it’s certainly not the case that each MCAS patient will suffer all (or even a majority) of these symptoms, symptoms commonly seen across the population of MCAS patients include:

  • Fatigue

  • Pain (often in a fibromyalgia-type pattern)

  • Lightheadedness

  • Headache

  • Itching

  • Tingling

  • Nausea

  • Feeling hot or cold or both (and intolerance of heat or cold)

  • Swelling in potentially any part of the body

  • Eye irritation

  • Difficulty taking a deep breath

  • Reflux of stomach acid

  • Brain fog

  • Rashes

  • Hives

  • Abdominal discomfort

  • Throat irritation

  • Fast or irregular heartbeats (palpitations, tachycardia)

  • Sweats

  • Environmental allergies and medication and chemical sensitivities

  • Chest discomfort or pain

  • Easy bleeding or bruising

  • Diarrhea or constipation

  • Difficulties with swallowing

  • Flushing

  • Anomalies with vision

  • Irritation/sores in the mouth

  • Waxing/waning enlargement and tenderness of lymph nodes

  • Urinary frequency or hesitancy

  • Frequent sense of urinary tract infection despite urine tests often showing no infection

  • Frequent or odd infections

  • Poor healing

  • Sinusitis

  • Unexplained weight gain or loss

  • Dental deterioration despite good dental hygiene

  • Cough

  • Anxiety/panic

  • Unusually uncomfortable or unusually heavy menstruation

  • Asthma

  • Hair thinning/loss

  • Depression

  • Insomnia

  • Tremor

  • Brittleness and ridging of nails,

  • Unusually vigorous insect bite reactions

HOW IS Mast Cell Activation Syndrome DIAGNOSED?

Although there is not yet global consensus on one set of diagnostic criteria, MCAS is diagnosed upon identifying in the patient:

(1) A clinical presentation (i.e., history and exam findings) consistent with chronic inappropriate mast cell mediator release

(2) Absence of any other evident disease which could better account for the full range and duration of all the symptoms and findings in the patient

(3) Laboratory evidence of mast cell activation

Laboratory evidence generally includes elevated levels in blood and/or urine of mediators relatively specific to the mast cell but may also include biopsies of various tissues (most commonly the gastrointestinal tract) showing mildly to moderately increased numbers of normal-shaped mast cells (in contrast to the greatly increased numbers and (commonly) abnormal shape of mast cells in mastocytosis).

Some of the mast cell mediators tested in this work-up are very sensitive to heat, requiring careful attention to continuous chilling of the specimens sent for mediator testing. Certain medications, too, can disturb levels of certain mediators, requiring careful review of the medication list prior to testing and temporary suspension of potentially confounding medications for a few days before specimen collection.

HOW IS Mast Cell Activation Syndrome TREATED?

Since it’s difficult for medications to control the dysfunctional mast cells in MCAS while the patient continues to expose himself to triggers, it’s important for the MCAS patient to identify triggers as precisely as possible and then do her best to avoid them. It is possible that as the disease comes under better control, some tolerance for those triggers may be regained. Beyond avoidance of triggers, there is a wide range of medications shown to be helpful in controlling the disease. Treatment typically begins with antihistamines but can go on to include other medications, including some natural and some pharmaceutical. Although it’s encouraging that most MCAS patients eventually find a helpful individualized treatment regimen, the state of mast cell disease science remains so immature that there are no methods yet established to predict which treatments are most likely to help which symptoms in which patients, therefore requiring a “trial-and-error” approach. With sufficient patience, persistence, and a methodical approach, most MCAS patients eventually reach the goal of feeling significantly better than the pre-treatment baseline the majority of the time. For most of the medications reasonable to try in MCAS, it becomes apparent only a month into the trial of any given medication whether that medication will be a “keeper” or whether it will not be helpful and should be stopped. MCAS patients typically move through a series of medication trials in relatively quick fashion until the goal is reached. The disease is quite variable, so while some patients may find helpful treatment within a few months, other patients may need to spend more than a year or two trying many medications before helpful therapy is identified.

The information provided in this page is intended to encourage, not replace, direct patient-health professional relationships. This web site is not intended to replace the advice of a patient-physician relationship.

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