Published: 18 Jun 2025

ICD9: 238.5      ICD10: D47.02      ICD11: 2A21.Z

Mastocytosis is a rare disorder characterized by an abnormal accumulation of mast cells in one or more organs of the body.
Mast cells are part of the immune system and are involved in allergic reactions. They release substances like histamine that cause inflammation.

Here's a breakdown of key aspects:

What are Mast Cells?

Immune Cells: Mast cells are a type of white blood cell that reside in tissues throughout the body, particularly in the skin, lungs, digestive tract, and bone marrow.
Mediators of Inflammation: They contain granules filled with chemicals like histamine, heparin, tryptase, and cytokines. When activated (by allergens, irritants, or other triggers), these chemicals are released, causing inflammation and a range of symptoms.
Protective Role: Under normal circumstances, mast cells play a vital role in defending the body against parasites and other pathogens.

What Happens in Mastocytosis?

Overproduction: In mastocytosis, the bone marrow produces too many mast cells.
Accumulation: These excess mast cells accumulate in various organs, leading to a variety of symptoms depending on the location of the accumulation.
Activation: The accumulated mast cells can become easily activated and release their inflammatory mediators, even without a clear trigger.

Types of Mastocytosis:

Mastocytosis is broadly classified into two main types:

Cutaneous Mastocytosis (CM): This type primarily affects the skin. It's most common in children.
Urticaria Pigmentosa (UP): The most common form of CM. It's characterized by brownish-red spots or bumps on the skin that itch and swell when rubbed (Darier's sign).
Diffuse Cutaneous Mastocytosis (DCM): A less common form that involves widespread thickening of the skin.
Mastocytoma: A single, isolated mast cell tumor on the skin.

Systemic Mastocytosis (SM): This type affects internal organs, such as the bone marrow, gastrointestinal tract, liver, spleen, and lymph nodes. It's more common in adults. SM is further subdivided into:
Indolent Systemic Mastocytosis (ISM): The most common form of SM. Symptoms are generally mild to moderate.
Smoldering Systemic Mastocytosis (SSM): A more aggressive form of SM with more significant organ involvement.
Aggressive Systemic Mastocytosis (ASM): A rare and serious form of SM that can cause organ damage and failure.
Mast Cell Leukemia (MCL): A very rare and aggressive form of SM in which large numbers of abnormal mast cells are found in the blood.
Systemic Mastocytosis with Associated Hematologic Neoplasm (SM-AHN): Mastocytosis occurring with another blood disorder (like myelodysplastic syndrome or myeloproliferative neoplasm).

Symptoms of Mastocytosis:

The symptoms of mastocytosis vary depending on the type and the organs involved. Common symptoms include:

Skin: Itching, hives, flushing, skin lesions (macules, papules, nodules), Darier's sign (whealing of skin when rubbed).
Gastrointestinal: Abdominal pain, nausea, vomiting, diarrhea, malabsorption.
Cardiovascular: Low blood pressure (hypotension), rapid heartbeat (tachycardia), fainting.
Respiratory: Wheezing, shortness of breath, nasal congestion.
Musculoskeletal: Bone pain, osteoporosis.
Neurological: Headache, fatigue, cognitive dysfunction.
Anaphylaxis: Severe allergic reaction that can be life-threatening.
Other: Fatigue, anxiety, depression, enlarged liver or spleen, enlarged lymph nodes.

Causes of Mastocytosis:

Genetic Mutation: In most cases of systemic mastocytosis, there's a genetic mutation in the *KIT* gene, which affects the development and survival of mast cells. This mutation is usually acquired, not inherited.
Unknown in Cutaneous Mastocytosis: The exact cause of cutaneous mastocytosis is often unknown.

Diagnosis of Mastocytosis:

Diagnosis usually involves:

Physical Examination: Evaluation of symptoms and skin findings.
Skin Biopsy: To examine skin tissue for mast cells.
Bone Marrow Biopsy: To assess mast cell infiltration in the bone marrow (especially in suspected systemic mastocytosis).
Blood Tests: Measurement of mast cell mediators (like tryptase), genetic testing for *KIT* mutations.
Urine Tests: Measurement of histamine metabolites.
Imaging Studies: X-rays, CT scans, or ultrasounds to evaluate internal organs.

Treatment of Mastocytosis:

Treatment focuses on managing symptoms and preventing mast cell activation. It depends on the type and severity of mastocytosis. Options include:

H1 and H2 antihistamines: To block the effects of histamine.
Mast cell stabilizers (e.g., cromolyn sodium, ketotifen): To prevent mast cells from releasing their mediators.
Leukotriene inhibitors (e.g., montelukast): To block the effects of leukotrienes, another inflammatory mediator.
Epinephrine auto-injector (EpiPen): For emergency treatment of anaphylaxis.
Corticosteroids: To reduce inflammation.
Omalizumab (anti-IgE therapy): For severe symptoms.
Chemotherapy: For aggressive systemic mastocytosis or mast cell leukemia.
Tyrosine Kinase Inhibitors (e.g., midostaurin): Target the *KIT* mutation in some cases of advanced systemic mastocytosis.
Avoidance of Triggers: Identifying and avoiding things that trigger mast cell activation (e.g., certain foods, medications, insect stings, temperature extremes).

Prognosis:

Cutaneous Mastocytosis: In children, cutaneous mastocytosis often resolves spontaneously by puberty.
Systemic Mastocytosis: The prognosis varies depending on the type of SM. Indolent SM has a good prognosis, while aggressive SM and mast cell leukemia have a poorer prognosis.

Important Considerations:

Rare Disease: Mastocytosis is a rare disease, so it can be challenging to diagnose.
Variable Presentation: The symptoms can be very variable, making diagnosis even more difficult.
Individualized Treatment: Treatment needs to be tailored to the individual patient and the specific type of mastocytosis.
Specialist Care: It's important to be managed by a doctor who has experience with mastocytosis, such as an allergist/immunologist or hematologist.
Support Groups: Support groups can provide valuable information and emotional support.

This information is for general knowledge and educational purposes only, and does not constitute medical advice. If you suspect you may have mastocytosis, it's crucial to consult with a qualified healthcare professional for diagnosis and treatment.