Systemic mastocytosis (SM) is a chronic, progressive disease with symptoms that gradually worsen over time. Mast cellMast cell A type of white blood cell produced in the bone marrow. They help defend against infections and play a key role in allergic reactions. In SM, mast cells become overactive and build up throughout the body. activity causes long-term damage to internal organs and connective tissue, leading to deterioration in function. Disease progression is tracked by monitoring the evolution of symptoms, performing regular medical tests (such as blood tests) and measuring the impact on quality of life.
The subtypes of SM
What is SM?
Systemic mastocytosisMastocytosis Rare disease caused by the buildup of mast cells. Cutaneous mastocytosis primarily affects the skin and is more common in children, while systemic mastocytosis affects internal organs and is more common in adults. (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.
There are 5 different subtypes of SM, each with a distinct level of aggressiveness and long-term prognosis:
- Indolent SMIndolent SM A subtype of nonadvanced SM caused by the abnormal accumulation of mast cells in the bone marrow and other organs. Indolent SM accounts for around 90% of SM cases. (ISM): The most common subtype, with milder symptoms that affect primarily the skin and gastrointestinal tract. It often stays stable over a number of years.
- Smoldering SMSmoldering SM A subtype of nonadvanced SM, with a higher mast cell burden than the indolent subtype. Smoldering SM has a higher likelihood of progressing to an advanced form. (SSM): A slow progressing subtype with a more significant burden.
- Aggressive SMAggressive SM A subtype of advanced SM marked by a high mast cell burden that leads to organ damage. Aggressive SM accounts for less than 10% of SM cases. (ASM): This subtype progresses rapidly, leading to organ damage and a reduced life expectancy.
- SM with an associated hematologic neoplasm (SM-AHN): Patients with this subtype have a blood disorder as well as SM. It aggressively damages organs and reduces life expectancy.
- Mast cell leukemiaMast cell leukemia The most severe subtype of SM, caused by the rapid buildup of immature mast cells in the bone marrow and blood. Mast cell leukemia accounts for less than 5% of SM cases and has a poor prognosis. (MCL): A rare, aggressive cancer, with a short life expectancy (typically two to six months).
Monitoring disease progression in SM
In many patients, symptoms remain stable for years. If symptoms are worsening or new symptoms appear, it may be the disease progressing to a new subtype.
Your health care team will conduct blood tests to:
- Check for anemia or thrombocytopenia (low platelet count) which could point to complications related to the bone marrow.
- Measure tryptaseTryptase A protein enzyme that is primarily produced by mast cells and stored in small pockets within the cells, known as granules. High levels of tryptase are a key indicator of SM. levels to monitor mast cell activity.
A liver enzyme test will assess liver function, and a gastrointestinal biopsy is useful to measure the mast cell activity. Imaging such as radiography, CT or MRI or PET/CT are also valuable in determining disease progression.
Read more about SM prognosis
Signs of progression in SM
Tracking your symptoms’ severity, duration and frequency in a symptom diary is the best way to monitor disease progression. It is important to build the habit of keeping a detailed description of your symptoms, and how they impact your overall physical and mental well-being and daily life. By being consistent, you will create a clear picture of how your disease is evolving.
Signs that your SM is progressing include:
- AnaphylaxisAnaphylaxis A severe allergic reaction that can turn fatal without treatment. Patients with SM are at a higher risk of developing anaphylaxis. reactions that are more frequent and more severe
- Worsening symptoms of nausea, vomiting, abdominal pain or diarrhea
- Severe skin reactions that don’t heal
- Bone pain or injury that could indicate the onset of osteoporosis
- An enlarged liver or spleen that may present as swelling of the abdomen
- Unexplained weight loss
- Persistent fatigue and weakness
Disease progression requires a change in treatment to try to slow its evolution and better manage symptoms to reduce the associated pain and discomfort.
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