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Author: Vanessa Ngan, Staff Writer, 2003. Updated by Adjunct Assoc. Prof. Amanda Oakley, Dermatologist, Hamilton, New Zealand. January 2019.
Mastocytoma is the name given to a form of cutaneous mastocytosis in which there is a dermal accumulation of mast cells forming one to thee solitary lesions .
Mastocytoma is most often diagnosed in an infant aged 0 to 3 months of age. They are rarely diagnosed in an adult . Mastocytoma is not usually familial.
Mastoma has been associated with a mutation of the KIT gene, which codes for a transmembrane tyrosine receptor on the mast cell responsible for its growth and function .
Activation of mast cells causes them to release histamine and other chemicals, which causes localised redness, swelling, itching, and, sometimes, blistering.
One to three mastocytomas usually appear in early childhood within the first few months of age. They can occur on any site of the body
Typical characteristics of mastocytoma are:
Occasionally localised or generalised flushing may occur when the mast cells release chemicals such as histamine into the skin.
Darier sign in mastocytoma
Mastocytoma can usually be diagnosed clinically, especially when a positive Darier sign is elicited. Dermatoscopy is non-specific , and the usual patterns seen in melanocytic naevus are absent. Blood tests are not required.
A skin biopsy reveals a monomorphous mononuclear cell infiltrate that stains positively with a c-KIT and tryptase immunoperoxidase stains [2,3].
At first, it is common for symptomatic mastocytoma to be thought to be a persistent insect bite reaction. If the lesion is not itchy, a congenital or early-onset melanocytic naevus may be considered.
If Darier sign is positive in adult-onset mastocytoma, the possibility of more widespread cutaneous mastocytosis or systemic mastocytosis should be considered, especially if there are systemic symptoms such as flushing.
Scratching or trauma to the lesion should be minimised to avoid itch, swelling, and blistering.
A mastocytoma in a cosmetically sensitive area may be excised , but localised urtication may persist within the scar .
Mastocytomas arising in infancy usually disappear before puberty .
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