Cutaneous mastocytosis

Cutaneous mastocytosis is a form of mastocytosis that primarily affects the skin. There are three main forms that vary in severity: maculopapular cutaneous mastocytosis (also called urticaria pigmentosa), solitary cutaneous mastocytoma, and diffuse cutaneous mastocytosis. There is also an exteremely rare form called telangiectasia macularis eruptiva perstans.^[2][6]

Maculopapular cutaneous mastocytosis, the most common form of cutaneous mastocytosis, is characterized by itchy, brown patches on the skin. Although these patches may be mistaken for freckles or bug bites initially, they typically persist and gradually increase in number over several months to years. In young children, the patches may form a blister if itched or rubbed. Itching may worsen with changes in temperature, strenuous activity, emotional stress, and/or certain medications. Maculopapular cutaneous mastocytosis is most commonly seen in infants and young children and often fades by the teenaged years. In some cases, this condition may not develop until adulthood. These later onset cases generally last long-term and are more likely to progress to systemic mastocytosis.^[2][6][7]

Solitary cutaneous mastocytoma is a localized form of cutaneous mastocytosis. Like maculopapular cutaneous mastocytosis, this form is typically diagnosed in young children. However, it is characterized by an itchy area of reddish or brown skin that is often thickened. When itched, these patches of skin may swell, redden, and/or blister. This form typically resolves spontaneously with age.^[2][6][8]

Diffuse cutaneous mastocytosis, the most severe form of cutaneous mastocytosis, usually develops in infancy. Unlike the other forms of cutaneous mastocytosis, it affects most or all of the skin rather than appearing as distinct patches. In people affected by this condition, the skin is leathery and thickened. It may appear normal, yellowish-brown, or red in color. In some cases, there may also be widespread blistering. Additional symptoms may include hypotension, diarrhea, gastrointestinal bleeding, reddening of the skin (flushing), and anaphylactic shock.^[1][2][6]

The rarest form of cutaneous mastocytosis is called telangiectasia macularis eruptiva perstans. Unlike the other forms of cutaneous mastocytosis, this form is primarily diagnosed in adults and is generally not associated with pruritus and blistering. People affected by this condition have persistent brown patches of skin and extensive telegiactasia. Rarely, this form may progress to systemic mastocytosis.^[1][2]

Most cases of cutaneous mastocytosis are caused by changes (mutations) in the KIT gene. This gene encodes a protein that helps control many important cellular processes such as cell growth and division; survival; and movement. This protein is also important for the development of certain types of cells, including mast cells (immune cells that are important for the inflammatory response). Certain mutations in the KIT gene can leads to an overproduction of mast cells. In cutaneous mastocytosis, excess mast cells accumulate in the skin, leading to the many signs and symptoms of the condition.^[1][9]

Most cases of cutaneous mastocytosis are not inherited. They occur spontaneously in families with no history of the condition and are due to somatic changes (mutations) in the KIT gene. Somatic mutations occur after conception and are only present in certain cells. Because they are not present in the germ cells (egg and sperm), they are not passed on to the next generation.^[1][6]

Cutaneous mastocytosis can rarely affect more than one family member. In these cases, the condition is typically inherited in an autosomal dominant manner.^[4][10] This means that to be affected, a person only needs a change (mutation) in one copy of the responsible gene in each cell. A person with familial cutaneous mastocytosis has a 50% chance with each pregnancy of passing along the altered gene to his or her child.

A diagnosis of cutaneous mastocytosis is typically suspected based on the presence of suspicious signs and symptoms. A skin biopsy that reveals a high number of mast cells (immune cells that are important for the inflammatory response) confirms the diagnosis.^[1][6]

Unfortunately it can sometimes be difficult to differentiate cutaneous mastocytosis from systemic mastocytosis. Additional tests may, therefore, be ordered to further investigate the risk for systemic disease. A bone marrow biopsy and specialized blood tests may be recommended in adults with cutaneous mastocytosis since they are at a higher risk for systemic mastocytosis. Affected children typically do not undergo a bone marrow biopsy unless blood tests are abnormal.^[11]

Although there is currently no cure for cutaneous mastocytosis, treatments are available to manage the symptoms of the condition. In general, it is recommended that affected people avoid things that trigger or worsen their symptoms when possible. Certain medications such as oral antihistamines and topical steroids are often prescribed to relieve symptoms. Affected adults may also undergo photochemotherapy which can help alleviate itching and improve the appearance of the patches; however, the condition is likely to recur within six to twelve months of the last treatment. People at risk for anaphylactic shock and/or their caregivers should be trained in how to recognize and treat this life-threatening reaction and should carry an epinephrine autoinjector at all times.^[1][5][6]

The long-term outlook (prognosis) for people affected by cutaneous mastocytosis varies depending on the age at diagnosis. The prognosis is typically excellent in children who develop symptoms before age 2 as approximately 80% of these cases resolve before puberty. The remaining cases may persist as cutaneous mastocytosis or progress to systemic disease. Risk factors for progression to systemic mastocytosis include later onset of the skin symptoms (after age 2), persistence of skin symptoms past adolescence, and abnormal blood counts. In very rare cases, the condition may progress to aggressive forms of mast cell disease such as mast cell sarcoma (solid tumor of cancerous mast cells) or mast cell leukemia (rare disease of circulating cancerous mast cells).^[3] [5]

Cutaneous mastocytosis that develops after age 2 or in adults generally does not resolve. Approximately 90% of affected adults also have evidence of systemic mastocytosis at the time of diagnosis. Later onset cases also have a higher risk of malignant (cancerous) forms of mast cell disease.^[3] [5]