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Peter J. Delves

, PhD, University College London, London, UK

Last full review/revision Oct 2020| Content last modified Oct 2020
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Mastocytosis is mast cell infiltration of skin or other tissues and organs. Symptoms result mainly from mediator release and include pruritus, flushing, and dyspepsia due to gastric hypersecretion. Diagnosis is by skin or bone marrow biopsy or both. Treatment is with antihistamines and control of any underlying disorder.

Mastocytosis is a group of disorders characterized by proliferation of mast cells and infiltration of the skin, other organs, or both. Pathology results mainly from release of mast cell mediators, including histamine, heparin, leukotrienes, and various inflammatory cytokines. Histamine causes many symptoms, including gastric symptoms, but other mediators also contribute. Significant organ infiltration may cause organ dysfunction. Mediator release may be triggered by physical touch, exercise, alcohol, nonsteroidal anti-inflammatory drugs (NSAIDs), opioids, insect stings, or foods.

Etiology in many patients involves an activating mutation (D816V) in the gene coding for the stem cell factor receptor c-kit, which is present on mast cells. The result is autophosphorylation of the receptor, which causes uncontrolled mast cell proliferation.

Classification of Mastocytosis

Mastocytosis may be cutaneous or systemic.

Cutaneous mastocytosis

Cutaneous mastocytosis typically occurs in children. Most patients present with urticaria pigmentosa, a local or diffusely distributed salmon or brown maculopapular rash caused by multiple small mast cell collections. Nodular lesions and plaques can also develop. Less common are diffuse cutaneous mastocytosis, which is skin infiltration without discrete lesions, and mastocytoma, which is a large (1 to 5 cm) solitary collection of mast cells.

Cutaneous forms rarely progress to systemic disease in children but may do so in adults.

Images of Urticaria Pigmentosa

Systemic mastocytosis

Systemic mastocytosis most commonly occurs in adults and is characterized by multifocal bone marrow lesions; it often involves other organs, most commonly skin, lymph nodes, liver, spleen, or gastrointestinal (GI) tract.

Systemic mastocytosis is classified as

  • Indolent mastocytosis, with no organ dysfunction and a good prognosis

  • Mastocytosis associated with other hematologic disorders (eg, myeloproliferative disorders, myelodysplasia, lymphoma)

  • Aggressive mastocytosis, characterized by impaired organ function

  • Mast cell leukemia, with > 20% mast cells in bone marrow, no skin lesions, multiorgan failure, and a poor prognosis

Symptoms and Signs of Mastocytosis

Skin involvement is often pruritic in mastocytosis—whether a single mastocytoma or more diffuse disease. The following may worsen itching:

  • Changes in temperature

  • Contact with clothing or other materials

  • Use of some drugs (including NSAIDs)

  • Consumption of hot beverages, spicy foods, or alcohol

  • Exercising

Stroking or rubbing skin lesions causes urticaria and erythema around the lesion (Darier sign); this reaction differs from dermatographism, which involves normal skin.

Systemic symptoms can occur with any form. The most common is flushing; the most dramatic are anaphylactoid and anaphylactic reactions with syncope and shock.

Other symptoms include epigastric pain due to peptic ulcer disease, nausea, vomiting, chronic diarrhea, arthralgias, bone pain, and neuropsychiatric changes (eg, irritability, depression, mood lability). Hepatic and splenic infiltration may cause portal hypertension with resultant ascites.

Diagnosis of Mastocytosis

  • Clinical evaluation

  • Skin lesion biopsy and sometimes bone marrow biopsy

Diagnosis of mastocytosis is suggested by clinical presentation. Diagnosis is confirmed by biopsy of skin lesions and sometimes of bone marrow. Multifocal, dense infiltrates of mast cells are present.

Tests may be done to rule out disorders that cause similar symptoms (eg, anaphylaxis Anaphylaxis Anaphylaxis is an acute, potentially life-threatening, IgE-mediated allergic reaction that occurs in previously sensitized people when they are reexposed to the sensitizing antigen. Symptoms... read more , pheochromocytoma, carcinoid syndrome, Zollinger-Ellison syndrome); these tests include the following:

Pearls & Pitfalls

  • Rule out disorders that cause symptoms similar to those of mastocytosis (eg, anaphylaxis, carcinoid syndrome, pheochromocytoma, Zollinger-Ellison syndrome).

If the diagnosis is uncertain, levels of mast cell mediators and their metabolites (eg, urinary N-methylhistamine, N-methylimidazole acetic acid) may be measured in plasma and urine; elevated levels support the diagnosis of mastocytosis. The level of tryptase (a marker of mast cell degranulation) is elevated in systemic mastocytosis but is typically normal in cutaneous mastocytosis.

A bone scan, GI workup, and identification of the D816V c-kit mutation can also be helpful in cases where the diagnosis requires confirmation.

Treatment of Mastocytosis

  • For cutaneous mastocytosis, H1 blockers and possibly psoralen plus ultraviolet light or topical corticosteroids

  • For systemic mastocytosis, H1 and H2 blockers and sometimes cromolyn

  • For aggressive forms, interferon alfa-2b, corticosteroids, or splenectomy

Cutaneous mastocytosis

Adults with cutaneous forms may be treated with psoralen plus ultraviolet light or with topical corticosteroids once or twice a day.

Mastocytoma usually involutes spontaneously and requires no treatment.

Systemic mastocytosis

All patients should be treated with H1 and H2 blockers and should carry a prefilled, self-injecting epinephrine syringe.

Aspirin controls flushing but may enhance leukotriene production, thereby contributing to other mast cell–related symptoms; it should not be given to children because Reye syndrome is a risk.

Cromolyn 200 mg orally 4 times a day (100 mg 4 times a day for children 2 to 12 years; not to exceed 40 mg/kg/day) may help by preventing mast cell degranulation. Ketotifen 2 to 4 mg orally twice a day is inconsistently effective. No treatment can reduce the number of tissue mast cells.

In patients with an aggressive form, interferon alfa-2b 4 million units subcutaneously once a week to a maximum of 3 million units a day induces regression of bone lesions. Corticosteroids (eg, prednisone 40 to 60 mg orally once a day for 2 to 3 weeks) may be required. Some limited evidence suggests that splenectomy may improve survival in patients with aggressive disease.

Cytotoxic drugs (eg, daunomycin, etoposide, 6-mercaptopurine) may be indicated for treatment of mast cell leukemia, but efficacy is unproved. Imatinib (a tyrosine kinase receptor inhibitor) may be useful when treating adults with aggressive systemic mastocytosis but is ineffective in patients with the D816V c-kit mutation. Midostaurin (a 2nd-generation tyrosine kinase receptor inhibitor) can be used to treat adults with aggressive systemic mastocytosis, systemic mastocytosis with associated hematologic disorders, or mast cell leukemia.

Key Points

  • Patients with cutaneous mastocytosis, usually children, typically present with a diffuse salmon or brown, often pruritic maculopapular rash.

  • Systemic mastocytosis causes multifocal bone marrow lesions, usually in adults, but often affects other organs.

  • All types can cause systemic symptoms (most commonly, flushing but sometimes anaphylactoid reactions).

  • For cutaneous mastocytosis, use H1 blockers to relieve symptoms, and in adults, consider treatment with psoralen plus ultraviolet light or topical corticosteroids.

  • For systemic mastocytosis, use H1 and H2 blockers and sometimes cromolyn, and for aggressive mastocytosis, consider interferon alfa-2b, systemic corticosteroids, or splenectomy.

  • Make sure all patients with mastocytosis carry a prefilled, self-injecting epinephrine syringe.

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