Systemic mastocytosis (SM) and mast cell activation syndrome (MCAS) are both mast cell disorders. As part of the immune system, mast cells release histamines, cytokines and other chemicals to fight infection.
In SM and MCAS, the mast cell activity is excessive, and these immune reactions trigger allergic reactions, causing physical and neurological symptoms. But there are key differences.
SM is a rare hematological disease characterized by mast cells that are overactive and accumulate in different parts of the body such as the bone marrow, liver, spleen, gastrointestinal tract and lymph nodes.
What is SM?
How does SM work?
In SM, mast cells multiply abnormally and accumulate in the skin, bones and internal organs. When an allergic reaction is triggered by such factors as pollen, insect bites, some foods, certain medications, sudden fluctuations in temperature, emotional and physical stress or alcohol, the response is amplified, and symptoms can range from mild to severe.
Learn more about SM signs and symptoms
Symptoms include hives, flushing, skin irritations, bone and joint pain, brain fog, mood changes, fatigue, headache, dizziness, gastrointestinal problems such as abdominal pain, nausea, vomiting and diarrhea and, in severe cases, anaphylaxis.
Medication such as antihistamines, along with lifestyle and diet modifications, help to prevent or manage daily symptoms.
What is mast cell activation syndrome?
MCAS is characterized by frequent episodes of a variety of symptoms, including headaches, brain fog, shortness of breath, flushing, itchy skin, hives, swelling of the face, constipation or diarrhea, vomiting, stomach pain, joint pain, heart palpitations, fainting and anaphylaxis.
MCAS is considered to be less severe than SM and is often diagnosed once SM has been ruled out.
SM vs MCAS
SM and MCAS have enough similarities that they are often confused with one another in the search for a diagnosis. Here are some of the similarities.
- SM and MCAS both involve excessive mast cell activity.
- SM and MCAS symptom triggers are similar, including emotional stress, certain foods and medications, alcohol, perfumes, pollen, physical exercise, insect bites and friction on the skin,
- SM and MCAS share similar symptoms, namely skin irritations, gastrointestinal issues, respiratory issues and anaphylaxis in serious cases.
- Treatment of SM and MCAS symptoms is through medication, namely antihistamines and mast cell membrane-stabilizing medications.
- SM and MCAS both significantly affect the quality of life of people living with the symptom burden.
What is the main difference between the two mast cell disorders? In MCAS, mast cells do not proliferate abnormally but rather are over-activated. This means that extra mast cells do not accumulate in the body—as in SM—eliminating the risk of long-term problems with the internal organs.
Additionally, MCAS can develop in children and adults, whereas SM is mainly diagnosed in adults around 50 years old.
