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# Mastocytosis (cutaneous and systemic)

Too many mast cells build up in the skin or inside the body. Their chemicals cause flushing, itchy spots, gut upset and sometimes severe allergic reactions.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Skin](https://durgical.com/en/anatomy/skin/)
- [Spleen](https://durgical.com/en/anatomy/spleen/)
- [Liver](https://durgical.com/en/anatomy/liver/)
- [Stomach](https://durgical.com/en/anatomy/stomach/)
- [Duodenum](https://durgical.com/en/anatomy/duodenum/)
- [Para-aortic lymph nodes](https://durgical.com/en/anatomy/intermediate-lumbar-nodes/)

## Why it happens

- [Oncogenes: RAS, MYC, HER2, BCR-ABL and the table to know](https://durgical.com/en/general-pathology/oncogenes-ras-myc-her2-bcr-abl-and-the-table-to-know/)
- [Histamine, serotonin, bradykinin and the plasma protein cascades](https://durgical.com/en/general-pathology/histamine-serotonin-bradykinin-and-the-plasma-protein-cascades/)
- [Connective tissue proper: cells and fibres](https://durgical.com/en/histology/connective-tissue-proper-cells-and-fibres/)

## What it is

A group of disorders in which clonal mast cells accumulate in the skin (cutaneous mastocytosis) or in internal organs such as bone marrow, gut, liver and spleen (systemic mastocytosis). Symptoms come from mediators released by mast cells and, in advanced forms, from organ infiltration.

## Who gets it

Rare, estimated around 1 in 10 000 to 20 000 people. Childhood forms usually start in the first year of life, are mostly limited to the skin and often fade by adolescence; adult forms are usually systemic, most often the indolent type.

## Causes

- Acquired (somatic) activating mutation of the KIT receptor, most often KIT D816V, in most adults
- Other KIT mutations in many children
- Additional mutations (such as TET2, SRSF2, ASXL1, RUNX1) in advanced forms

## Risk factors

- Not inherited in most cases; rare familial forms exist
- Triggers of mast-cell release: insect stings, heat, friction, alcohol, stress, opioids, aspirin and NSAIDs, contrast media and anaesthesia

## Pathophysiology

Constant activation of KIT, the receptor for stem cell factor, makes mast cells survive and multiply. They release histamine, tryptase, prostaglandins and leukotrienes, causing flushing, itching, gastric acid excess, diarrhoea, low blood pressure and anaphylaxis. In advanced disease mast cells infiltrate bone marrow, liver, spleen and bone, causing cytopenias, organomegaly, malabsorption and osteolysis or osteoporosis.

## Classification

- Cutaneous mastocytosis: urticaria pigmentosa (maculopapular), diffuse cutaneous, and solitary mastocytoma
- Indolent systemic mastocytosis (most common adult form)
- Smouldering systemic mastocytosis
- Systemic mastocytosis with an associated haematological neoplasm
- Aggressive systemic mastocytosis and mast cell leukaemia (rarest, most severe)

## Symptoms and signs

- Small red-brown spots or papules on the trunk and thighs (urticaria pigmentosa) that itch and swell
- Darier sign: rubbing a lesion makes it red, raised and itchy
- Episodes of flushing, palpitations, lightheadedness or fainting
- Abdominal pain, heartburn, nausea and diarrhoea
- Bone pain, fractures, fatigue and difficulty concentrating
- Enlarged liver, spleen or lymph nodes in advanced forms

## Red flags

- Anaphylaxis: low blood pressure, fainting, wheeze or throat tightness, often after a sting, drug or anaesthesia
- Unexplained anaphylaxis to a wasp or bee sting, especially with hypotension and no hives
- Falling blood counts, weight loss, ascites or a fast-growing spleen (aggressive disease)
- Vertebral or other fragility fractures in a young adult

## Diagnosis

**Clinical**
Typical [skin](https://durgical.com/en/anatomy/skin/) lesions with a positive Darier sign suggest the diagnosis, especially in children. Recurrent flushing, unexplained anaphylaxis or osteoporosis in an adult prompts a search for systemic disease.

**Tests**
Skin biopsy for cutaneous forms. Baseline serum tryptase is the key screening test (a persistently raised level suggests systemic disease). Bone marrow biopsy shows multifocal dense mast-cell aggregates, which is the major WHO criterion; minor criteria include spindle-shaped mast cells, CD25 (or CD2, CD30) expression and the KIT D816V mutation. Blood count and [liver](https://durgical.com/en/anatomy/liver/) tests look for organ damage.

**Imaging**
Bone densitometry for osteoporosis; abdominal ultrasound or CT for liver and [spleen](https://durgical.com/en/anatomy/spleen/) enlargement in suspected advanced disease.

## Differential diagnosis

- Anaphylaxis or allergy from other causes
- Mast cell activation syndrome without clonal mast cells
- Carcinoid syndrome and pheochromocytoma (flushing)
- Chronic urticaria
- Hypereosinophilic syndrome and other myeloid neoplasms

## Goal of treatment

Control mediator symptoms, prevent and treat anaphylaxis, protect bone, and in advanced disease reduce the mast-cell burden to restore organ function.

## Treatment

**Lifestyle**
Identifying and avoiding personal triggers, with special planning before surgery, anaesthesia, contrast studies and insect exposure.

**Medical**
H1 and H2 antihistamines, oral cromolyn (a mast-cell stabiliser), leukotriene antagonists and proton-pump inhibitors for symptoms; glucocorticoids in severe flares.

**Acute**
Epinephrine is the first-line treatment for anaphylaxis; people with systemic disease usually carry an epinephrine auto-injector.

**Medical**
KIT tyrosine kinase inhibitors active against D816V (such as midostaurin or avapritinib) or cladribine for advanced forms; allogeneic transplant for selected aggressive disease.

**Follow-up**
Serum tryptase, blood counts and bone density over time; venom immunotherapy may be offered after sting anaphylaxis.

## Complications

- Recurrent, sometimes fatal, anaphylaxis
- Osteoporosis, fractures and osteolytic bone lesions
- Peptic ulcer disease and malabsorption
- Cytopenias, liver dysfunction with portal hypertension and ascites in advanced disease
- Associated myeloid cancer or transformation to mast cell leukaemia

## Prognosis

Childhood cutaneous mastocytosis often improves or resolves by puberty. Indolent systemic mastocytosis carries a near-normal life expectancy, while aggressive forms and mast cell leukaemia shorten survival markedly.

## Test yourself

Think of the answer, then tap the question to see it.

## What is Darier sign?

Rubbing a mastocytosis skin lesion causes local redness, swelling and itch from mast-cell degranulation.

## Which mutation is found in most adults with systemic mastocytosis?

The acquired activating KIT D816V mutation.

## Which blood test is the key screening marker for systemic mastocytosis?

Baseline serum tryptase.

## What is the first-line drug for anaphylaxis in mastocytosis?

Epinephrine (adrenaline).

## What is the usual course of cutaneous mastocytosis that begins in infancy?

It often improves or disappears by adolescence.

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## Related conditions

- [Anaphylaxis](https://durgical.com/en/conditions/anaphylaxis/)
- [Urticaria and angioedema](https://durgical.com/en/conditions/urticaria-and-angioedema/)
- [Carcinoid syndrome](https://durgical.com/en/conditions/carcinoid-syndrome/)
- [Phaeochromocytoma](https://durgical.com/en/conditions/phaeochromocytoma/)
- [Osteoporosis](https://durgical.com/en/conditions/osteoporosis/)
- [Peptic ulcer disease](https://durgical.com/en/conditions/peptic-ulcer-disease/)
- [Hypereosinophilic syndrome](https://durgical.com/en/conditions/hypereosinophilic-syndrome/)
- [Myelodysplastic syndromes](https://durgical.com/en/conditions/myelodysplastic-syndromes/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Mastocytosis](https://rarediseases.org/rare-diseases/mastocytosis/) (National Organization for Rare Disorders (NORD), 2024); [Systemic mastocytosis](https://medlineplus.gov/genetics/condition/systemic-mastocytosis/) (MedlinePlus Genetics, US National Library of Medicine, 2026).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/mastocytosis/