Mastocytosis is a rare condition characterized by the clonal proliferation and accumulation of altered mast cells (also known as tissue mast cells) in one or more organs. The most commonly affected sites include the skin, gastrointestinal tract, liver, spleen, and other internal organs.

Mastocytosis is divided into two main types:

Cutaneous mastocytosis (CM): affects only the skin
Systemic mastocytosis (SM): involves internal organs beyond the skin

Who Gets Cutaneous Mastocytosis?

CM is more common in children (about 65% of cases). In these cases, the disease is usually limited to the skin, has a benign course, and often resolves spontaneously by adolescence. Only a small percentage progresses to systemic disease.

In contrast, adults are more likely to be diagnosed with systemic mastocytosis, while isolated skin forms are rare (less than 5% of cases in adults).

There are three main types of cutaneous mastocytosis:

Maculopapular mastocytosis (including urticaria pigmentosa) – the most common
Diffuse cutaneous mastocytosis
Mastocytoma

Causes of Cutaneous Mastocytosis

Most cases are caused by gene mutations, which play a major role in both cutaneous and systemic forms of the disease. These mutations lead to an overproduction of mast cells, which release various bioactive mediators. This causes local or systemic inflammatory reactions.

Symptoms such as itching, redness, and swelling are typically caused by the release of these mediators.

Hereditary (familial) cases are extremely rare.

Symptoms and Clinical Presentation

The most typical presentation is a gradually spreading rash with pink or brown macules and papules. Less commonly, plaques, nodules, blisters, or visible blood vessels (telangiectasias) may appear.

The most commonly affected areas include:

Chest, trunk, and limbs
The face, scalp, palms, and soles are usually spared

Common associated symptoms:

Itching
Flushing
Rapid heartbeat
Low blood pressure
Abdominal pain
Nausea or vomiting

Mastocytoma is a form of CM that usually occurs in children. It appears as a single, oval, reddish-yellow plaque or patch, typically on the chest, face, neck, or limbs.

A classic sign of CM is a positive Darier's sign: when the skin is gently rubbed, the lesion becomes red and swollen or may even form a small blister.

Diagnosis

Diagnosis is based on:

Medical history and clinical appearance
Dermoscopy to magnify and analyze lesion structure
In uncertain or widespread cases: skin biopsy for histological confirmation

In children, biopsy is rarely required due to the often self-limiting nature of the disease.

Additional tests may include:

Blood tests, including liver and kidney function
Serum tryptase level
Ultrasound of abdominal organs (to evaluate liver, spleen, and lymph nodes)

Treatment

In many cases, treatment focuses on symptom control and avoiding triggers rather than complete removal of lesions.

Main strategies include:

Educating the patient about triggers that may activate mast cells and how to avoid them
Carrying an emergency adrenaline autoinjector and knowing how to use it, as anaphylactic reactions can occur
Use of topical or systemic medications as needed
Phototherapy (e.g., UVB or PUVA) in selected cases

Common Triggers That Can Activate Mast Cells

Patients should avoid or be cautious with:

Insect stings (bees, wasps, jellyfish)
Physical friction or pressure (massage, rubbing, tight clothing)
Surgical procedures or biopsies
Certain medications (e.g., some anti-inflammatory drugs, contrast agents, some cardiac drugs)
Extreme temperatures – heat or cold
Stress, intense physical exertion, fever, or alcohol