Mastocytosis

Mastocytosis is a rare condition in which too many mast cells build up in the skin, bone marrow or other organs. Mast cells are immune cells that release histamine and other chemicals during allergic reactions. Cutaneous mastocytosis affects only the skin and is most common in children, where it often improves by adolescence. Systemic mastocytosis usually starts in adults and is often linked to a KIT D816V gene change. Symptoms can include brownish skin spots that itch or swell when rubbed, flushing, itching, abdominal pain, diarrhea, bone pain, and severe allergic reactions (anaphylaxis), especially to insect stings. Advanced forms are rare.

Lab tests linked to mastocytosis:

• Doctors may order a baseline serum tryptase, measured when well, and KIT D816V testing in blood. Diagnosis of systemic mastocytosis usually needs a bone marrow biopsy. Skin lesions can be confirmed with a skin biopsy. Doctors may also order a CBC, liver tests and a bone density scan.

How results are read:

• A persistently raised baseline tryptase above 20 ng/mL can count as a minor criterion for systemic mastocytosis. Specialists adjust how it is read in hereditary alpha-tryptasemia and some related myeloid disorders. A normal tryptase doesn't rule out mastocytosis, especially when only the skin is affected.
• Mildly raised tryptase can also be due to hereditary alpha-tryptasemia, a common inherited trait, or kidney disease.
• Finding KIT D816V in blood or bone marrow supports systemic mastocytosis.
• Clusters of abnormal mast cells in the bone marrow are the main criterion for diagnosis.

When to see a doctor:

• See a doctor about skin spots that itch, swell or redden when rubbed, frequent flushing, or unexplained severe allergic reactions.
• If you have mastocytosis, ask about carrying an epinephrine auto-injector.
• Call your emergency number for swelling of the lips, tongue or throat, wheezing, difficulty breathing, dizziness or fainting.

Clinical takeaway: mastocytosis is diagnosed with skin or bone marrow biopsy, supported by serum tryptase and KIT D816V testing.