Specialty Immunology ICD-9-CM 757.33/202.60 | ICD-10 D89.4 | |
Mast cell activation syndrome (MCAS), also commonly referred to as mast cell activation disorder (MCAD), is an immunological condition in which mast cells inappropriately and excessively release chemical mediators, resulting in a range of chronic symptoms, sometimes including anaphylaxis or near-anaphylaxis attacks. Primary symptoms include cardiovascular, dermatological, gastrointestinal, neurological and respiratory problems.
Contents
Unlike mastocytosis, where patients have an abnormally increased number of mast cells, patients with MCAS have a normal number of mast cells that do not function properly and are defined as "hyperresponsive." MCAS is still a poorly understood condition and is a current topic of research.
MCAS is often found in patients with Ehlers–Danlos syndrome (EDS) and postural orthostatic tachycardia syndrome (POTS). It is also found in subset groups of patients with common variable immunodeficiency (CVID) and Lyme disease.
Symptoms and triggers
MCAS is a condition that affects multiple systems, generally in an inflammatory manner. Symptoms typically wax and wane over time, varying in severity and duration. Many signs and symptoms are the same as those for Mastocytosis, because both conditions result in too many mediators released by mast cells. It has many overlapping characteristics with recurrent idiopathic anaphylaxis, although there are distinguishing symptoms, specifically hives and angioedema.
Common symptoms include:
Symptoms can be caused or worsened by triggers, which vary widely and are patient-specific. Common triggers include:
Causes
There are no known causes, but the condition appears to be inherited. Symptoms of MCAS are caused by excessive chemical mediators inappropriately released by mast cells. Mediators include leukotrienes and histamines. The condition may be mild until exacerbated by stressful life events, or symptoms may develop and slowly trend worse with time.
Diagnosis
MCAS is often difficult to identify due to the heterogeneity of symptoms and the "lack of flagrant acute presentation." The condition can also be difficult to diagnose, especially since many of the numerous symptoms may be considered "vague". Patients often see many different specialties due to the inherent multisystem nature of the condition, and do not get diagnosed until a holistic view is taken by a diagnostician. Lack of awareness of MCAS by many medical professionals is currently a hurdle to proper diagnosis.
- Symptoms consistent with chronic/recurrent mast cell release:
Recurrent abdominal pain, diarrhea, flushing, itching, nasal congestion, coughing, chest tightness, wheezing, lightheadedness (usually a combination of some of these symptoms is present) - Laboratory evidence of mast cell mediator (N-methyl histamine, prostaglandin D2 or 11-beta- prostaglandin F2 alpha, leukotriene E4 and others)
- Improvement in symptoms with the use of medications that block or treat elevations in these mediators"
The World Health Organization has not yet published diagnostic criteria.
Treatment
Common pharmacological treatments include:
Fillers, binders and dyes in many medications are often the culprit in causing reactions, not necessarily the active agent, so alternative formulations and compounding pharmacies should be considered.
Lifestyle changes may also be needed. Avoidance of triggers is important. It should be emphasized that MCAS patients can potentially react to any new exposure, including food, drink, medication, microbes and smoke via inhalation, ingestion or touch.
A low histamine diet and other elimination diets can be useful in identifying foods that trigger or worsen symptoms. Many MCAS patients already have high histamine levels, so ingesting foods with high histamine or histamine liberators can worsen many symptoms such as vasodilation that causes faintness and palpitations.
Prognosis
There is no cure for MCAS. For most, symptoms wax and wane, but many can experience a general worsening trend over time. Lifespan for those with MCAS appears to be normal, but quality of life can range from mild discomfort to severely impaired. Some patients are impaired enough to be disabled and unable to work.
Epidemiology
MCAS is a relatively new diagnosis, being unnamed until 2007, and is believed to be very under-diagnosed. New findings are revealing that MCAS is much more prevalent than previously thought. It's currently estimated that 4.5% of the general population has tryptasemia, which is associated with mast cell activation syndrome.
History
It has been suggested in the literature for decades; however diagnostic criteria have been proposed only in 2010. The condition was first recognized in 1991, and finally named in 2007.