Mast Cell Activation Syndrome (MCAS)

Mast cell activation syndrome is a fairly recent addition to the immunologists’ repertory of diagnoses. Because it can sometimes be triggered by chemical agents, it is worthwhile outlining its main features. The diagnosis is based on one’s history and laboratory tests.

The precise mechanism is unclear but it is thought to be initiated by either a genetic predisposition and exposure to some of the factors mentioned below or a reactivity to some external agents, be they foods or chemicals, which then stimulate mast cells to produce a lot of histamine and other proteolytic enzymes. The tests normally used to diagnose “allergy” i.e. skin prick tests or immunoglobulin E antibodies are not relevant here, as we are not talking about “classic” allergies.

Symptoms of MCAS involve various systems such as skin (hives, angioedema), respiratory (breathlessness, wheezing, cough), gastrointestinal (vomiting, diarrhoea), general (anxiety, agitation, brain fog, sleep problems), eyes (inflammation, irritation, swelling). These can be persistent or intermittent and mild or severe to the point of anaphylaxis. They can be triggered by many different agents e.g. foods, natural biological inhalant allergens (pollens, dust mites, moulds) and environmental/airborne chemicals or volatile organic compounds, food chemicals such as benzoic acid, sulphites or salicylates, but this possibility is often overlooked by doctors and health professionals, not familiar with the condition.

Laboratory tests available today mainly focus on the detection of raised levels of N-methyl histamine, prostaglandin D2 or 11 beta-prostaglandin F2 alpha, leukotriene E4 and a few others. However, these are not routinely tested by GP’s or hospital departments. There must be a good percentage of people who experience symptoms of severe chemical sensitivity, who may have MCAS, but were never checked for it.

MCAS is known to be “controlled" with some antihistamines, some histamine-modifying drugs, leuco-trtiene antagonists and some non-steroid anti-inflammatories – but some of them might aggravate the condition, being some of its very “triggers”. Reducing foods high in histamine is also recommended and desensitisation for the underlying causes, using one of the modern methods of immunotherapy, usually works well.

Looking at the MCAS, it should be distinguished from the "unconventional" diagnosis of “histamine intolerance”, which is tested with the enzyme di-amine-oxidase (DAO) and can be managed with avoidance of histaminic foods and possibly desensitisation.

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