Mast cell activation syndrome (MCAS) is a condition where the mast cells in your body, which are part of your immune system, react to triggers that normally wouldn’t cause a problem, producing symptoms of an allergic reaction.
What is mast cell activation syndrome (MCAS)?
Most people have experienced or know someone with hay fever, hives or anaphylaxis. All three are allergic reactions that occur when mast cells release mediators.
Mast cells are an important part of our immune system. They are involved in wound healing, the formation of new blood vessels, and protection against infection. Mast cells are found in most tissues of the body, including bone marrow and around blood vessels. They are mainly found in tissues that interact with the environment, such as the skin, lungs, and gastrointestinal and urinary tracts.
Mast cell activation syndrome (MCAS) is very different to another condition that involves the mast cells called systemic mastocytosis. With MCAS, the mast cells are ‘overactive’ and it is now thought to be quite common. Mastocytosis is caused by having too many mast cells and it is a rare disorder.
How are ME/CFS and mast cell activation syndrome (MCAS) connected?
Mast cell activation syndrome (MCAS) is seen in people with hypermobile Ehlers–Danlos syndrome (hEDS), postural orthostatic tachycardia syndrome (POTS) and in 25% of people with ME/CFS[1]. It may also be involved in the symptoms of acute and long COVID.
If you believe you have MCAS, it is important to talk with your doctor, as they may need to rule this out as the cause of your symptoms. Some people with ME/CFS can also have MCAS.
If you are experiencing fatigue or symptoms, you feel may be post-exertional malaise (PEM) that is connected to ME/CFS, please review our information on ‘Stop. Rest. Pace.‘ and talk to your doctor about your concerns.
Diagnosis and treatment
Immunologists and haematologists are doctors who specialise in the immune system and blood cells. They may be able to diagnose and treat MCAS, but it is important to make sure that the specialist you see understands MCAS.
Diagnosis of MCAS may involve:
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- ruling out other medical conditions with similar symptoms
- measuring your level of tryptase, an enzyme that is released from mast cells into the bloodstream during an allergic reaction
- a 24-hour urine test to measure mast cell mediators.
If you are diagnosed with MCAS, your doctor will work with you to decide on the best treatment for you.
Some things you can do to help include:
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- Identifying and avoiding any known triggers
- Talking with your doctor or a dietician about whether a particular type of diet might be beneficial
- Finding out from your doctor about possible medication options.
Histamine intolerance
Histamine is found naturally in the body and in some foods. Normally, the body breaks histamine down using an enzyme called diamine oxidase (DAO). If you don’t have enough diamine oxidase, histamine can build up and cause symptoms.
There’s growing interest in how mast cells and histamine may relate to inflammation, irritable bowel syndrome and ME/CFS, but more research is still needed. You can read more about histamine intolerance and diamine oxidase (DAO) from Monash University by clicking here.
Reference
- Rohrhofer, J., Ebner, L., Schweighardt, J., Stingl, M., & Untersmayr, E. (n.d.). The clinical relevance of mast cell activation in myalgic encephalomyelitis/chronic fatigue syndrome. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12651186/