Mastocytosis

Mastocytosis is a term that describes a group of disorders that are caused by too many mast cells in the body. A mast cell is a type of blood cell made in the bone marrow that is involved in allergic reactions and fighting parasitic infections. Mast cells produce histamine, a chemical that can cause itching, sneezing, congestion, swelling, and wheezing. Mast cells can increase along with some non-cancerous (benign) conditions. Sometimes, certain types of cancers may begin from the growth of abnormal mast cells.

There are two general forms of mastocytosis: cutaneous (skin) and systemic (whole body).

Cutaneous mastocytosis

Cutaneous mastocytosis is an increase of mast cells in the skin. About 90% of people with mastocytosis have the cutaneous type. Subtypes of cutaneous mastocytosis include:

• Urticaria pigmentosa. The most common form of cutaneous mastocytosis is urticaria pigmentosa. Tan or red-brown spots (called lesions) on the skin are a main sign of urticaria pigmentosa. These spots generally appear on the midsection of the body at first, and then spread throughout the body. A person with this type of mastocytosis may also have nausea, vomiting, and diarrhea.
• Solitary mastocytoma. More common in infants and children than in adults, this type usually forms a large nodule [3 centimeters (cm) to 4 cm in diameter] on an arm or leg.
• Diffuse erythrodermic mastocytosis. Found most commonly in children younger than three years old, diffuse erythrodermic mastocytosis may not be noticeable when a child is born, but can later show up as a rapid thickening of the skin. Symptoms of systemic mastocytosis (see below) and blisters are also common.
• Telangiectasia macularis eruptiva perstans. This type of cutaneous mastocytosis is found mostly in adults. The main signs are lesions that do not itch and are smaller than those of urticaria pigmentosa (see above).

Systemic mastocytosis

Systemic mastocytosis involves internal organs throughout the body, including the gastrointestinal tract, bone marrow, liver, spleen, and lymph nodes. In 85% of people with systemic mastocytosis, the cutaneous mastocytosis subtype of urticaria pigmentosa developed first. The risk of developing systemic mastocytosis increases with age. Depending on the number of mast cells in an organ, it is classified as either indolent (grows slowly) or aggressive (grows quickly) mastocytosis. As the number of mast cells build up in an organ, the symptoms of the disease worsen.

Systemic mastocytosis can become malignant (cancerous). The risk of systemic mastocytosis becoming cancerous is 7% when the disease begins in childhood and as much as 30% in adults. Mast cell leukemia involves the blood, while mast cell sarcoma involves the soft tissues.

Find out more about basic terms used in this section.

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