There are six types of systemic mastocytosis. Each type has different symptoms, but in general, the higher the abnormal mast cell accumulation, the greater the likelihood of serious health complications.
Indolent Systemic Mastocytosis (ISM)
Indolent (slower growing) systemic mastocytosis is the most common form of systemic mastocytosis in adults. People usually have milder symptoms that develop over many years. Skin and gastrointestinal issues are common, and usually other organs aren’t affected.
People with ISM are at higher risk for severe episodes of anaphylaxis (a severe allergic reaction) than those with more aggressive forms of SM.
For people with ISM, the chances of progressing to more advanced disease are low — about 5 percent in a 10-year period, says Nikolai Podoltsev, MD, PhD, an associate professor of internal medicine specializing in hematology at Yale Medicine in New Haven, Connecticut.
Smoldering Systemic Mastocytosis (SSM)
Smoldering (slow-to-progress) systemic mastocytosis is an intermediate form of SM that requires more monitoring and management than ISM. Abnormal mast cells build up in the bone marrow, liver, or spleen, which can cause an enlarged spleen (splenomegaly) or enlarged liver (hepatomegaly).
SM With Associated Hematologic Neoplasm (SM-AHN)
This type of systemic mastocytosis occurs when the excessive growth of mast cells is combined with another blood disease, such myeloproliferative disorder (a condition in which the bone marrow produces too many blood cells) or acute myeloid leukemia. SM-AHN affects about one-fifth of people with systemic mastocytosis.
Aggressive Systemic Mastocytosis (ASM)
In aggressive systemic mastocytosis, mast cells infiltrate organs such as the liver, spleen, bone marrow, lymph nodes, and small intestine.
ASM may get worse quickly. As abnormal mast cells multiply in the bone marrow, they interrupt blood cell production, which can lead to conditions such as low white blood cell numbers (leukopenia) and low red blood cell numbers (anemia). Abnormal mast cells may also grow into your bones, making them weak and more likely to break.
Mast Cell Leukemia (MCL)
Very rarely, systemic mastocytosis becomes mast cell leukemia, in which too many immature mast cells are found in the bone marrow and blood. MCL is hard to treat and has a poor prognosis.
Mast Cell Sarcoma (MCS)
This is also a very rare condition in which solid tumors made of abnormal mast cells attack tissue. Diagnosing mast cell sarcoma is difficult, and the prognosis is poor.
Indolent and smoldering SM are less aggressive forms of the disease, whereas SM-AHN, ASM, MCL, and MCS are all considered advanced systemic mastocytosis (advSM), says Dr. Podoltsev.
