SM Basics

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 the accumulation of mast cells in different parts of the body.

Read on for some frequently asked questions (FAQs) about SM, along with their answers.

Who can be diagnosed with SM?

SM seems to affect men and women equally. Adults are more likely to develop the disease compared to children. The disease also seems to be more common among people of Caucasian descent. 

What causes SM?

In most cases, SM is caused by a sporadic mutation in the KIT oncogene. 

Does SM run in families?

SM is not considered a genetic disease, and the mutation in the KIT oncogene occurs sporadically during the lifetime of a patient.

However, in very rare cases, the disease has been seen to be passed down in families.

Can environmental factors trigger SM?

Although the symptoms of SM can develop on their own without any external trigger, there may be some environmental factors that drive the development of an SM attack. 

These may include alcoholic drinks, certain foods like spicy foods, some medications like non-steroid anti-inflammatory drugs (NSAID), muscle relaxants and anesthetics, sudden changes in temperature, exercise and physical activity, insect bites and physical or emotional stress.

What are the early signs of SM?

The early signs of SM may include fatigue, muscle pain, low blood pressure, lightheadedness, nausea, headache, difficulty with memory and concentration and malaise. 

Some patients may also experience severe allergic reactions known as anaphylaxisAnaphylaxis A severe allergic reaction that can turn fatal without treatment. Patients with SM are at a higher risk of developing anaphylaxis..

How do doctors diagnose SM?

A diagnosis of SM can be reached based on the results of blood tests, imaging tests, bone marrow biopsyBone marrow biopsy A procedure to collect a sample of bone marrow using a needle. Often used to examine the characteristics of mast cells and diagnose SM. and genetic tests.

A definite diagnosis can be reached if at least one major and one minor criteria or three minor criteria established by the World Health Organization (WHO) are fulfilled. The major criterion is the presence of multifocal 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. clusters in the bone marrow and/or extracutaneous organs. Minor diagnostic criteria include elevated serum 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, CD25/CD2/CD30 expression in mast cells and the presence of activating KIT mutations.

How common is SM?

SM is a rare disease. It is thought to affect one in 10,000 to 20,000 people worldwide.

What treatments are available?

There is currently no cure for SM, but there are some treatments that can alleviate the symptoms of the disease.

For milder forms of the disease, a doctor may prescribe antihistaminesAntihistamines Medications that block the effects of histamine, the chemical found in mast cells that is responsible for many of the symptoms of SM, as well as many allergic reactions., corticosteroids or anti-immunoglobulin E antibodies such as omalizumab. 

EpinephrineEpinephrine Also called adrenaline, this hormone is used in emergency situations to reverse symptoms during a severe allergic reaction (anaphylaxis). may be used to treat sudden attacks of anaphylaxis.

For more severe forms of the disease, treatment may include cladribine, midostaurin, interferon-alpha, or tyrosine kinase inhibitors such as imatinib.

In the case of aggressive disease, chemotherapy may be necessary, and when no other treatment option is effective, a stem cell transplant may be considered. 

Who can treat SM?

Patients newly diagnosed with SM will likely be treated by a hematologist, dermatologist, immunologist and gastroenterologist.

What is the prognosis?

The prognosis depends on the type of SM that a patient has. 

Patients with 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., which is the most common sub-type of the disease, have a normal life expectancy, while patients with 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., the most severe form of the disease, have a shortened life expectancy.

As a whole, the life expectancy of patients with SM is shorter than those of healthy people.