3.2.8 Cutaneous Mastocytosis

Grading & Level of Importance: B




Mastocytosis, mast cell disease.


Rare disease, most common in children. Prevalence 0.1 to 0.8% of dermatology consultations.


65% are observed in children below 15 years. Two  peaks of incidence, one between 6 months and 2 years (55%) and one  between 20 and 40 years (35%).


Proliferation of mast cells in the skin.

Aetiology & Pathogenesis

It is frequently caused by mutations in the KIT gene (KIT D816V) and is most often sporadic. MRGPRX2 activates mast cells, which in turn release tryptase and histamine with local or systemic symptoms.

Signs & Symptoms

Urticaria pigmentosa (maculopapular mastocytosis): many red-brown, maculopapular lesions, with variable flushes and pruritus (most common form). Diffuse cutaneous mastocytosis: diffuse erythema, skin infiltration, blistering (rare, in the first month of life). Localized mastocytosis (mastocytoma) is a single lesion (or sometimes 1-3 lesions), most often found in children. Mastocytosis skin lesions respond with an urticarial reaction spontaneously or after irritation (Darier's sign: wheal, erythema, itch).  Furthermore, a so called idiopathic mast cell activation syndrome (MACS) was recently introduced as an entity within the mast cell disorders. 


Cutaneous mastocytosis (urticaria pigmentosa and diffuse cutaneous mastocytosis) shows a disseminated appearance on the entire body. Mastocytoma is a unique lesion, or multiple (generally 1 to 3) lesions localized anywhere on the skin. MACS is a mast cell products release disorder without specific localization without diffuse increase of mast cells, as in the diffuse type.


The 2016 updated current WHO classification of mastocytosis identifies 3 forms of cutaneous mastocytosis: urticaria pigmentosa, diffuse cutaneous mastocytosis, and mastocytoma.

Laboratory & other workups

Serum tryptase levels are correlated with the mast cell tumor burden. A complete blood count is useful to screen for hematologic (medullary) involvement.


Dense perivascular infiltrates of mast cells which stain positively with Giemsa, toluidine blue (heterochromasia) or chloroacetate esterase (Leder-stain). Immunohistochemistry to stain mast cells (anti-CD117=KIT, anti-tryptase, and anti-CD25 antibodies).


If the disease appears in childhood, spontaneous remission is frequent. The adult version is generally clinically stable but mast cells may proliferate and lead to systemic symptoms.


In adults, flushes, hives, diarrhoea, vomiting, headache, depression, breathing problems, osteoporosis, visceral involvement, anaphylaxis (rare). Worsening of symptoms may be provoked by alcohol and certain food or drugs. 


Diagnosis is based on typical clinical features and confirmed by histopathology. At baseline, no additional workup is required in children. Serum tryptase levels, complete blood count, abdominal ultrasonography and osteodensitometry are performed in adults. In diffuse type  of mastocytosis and KIT anomaly a bone marrow aspiration is indicated.

Differential diagnosis

Lichen planus, disseminated granuloma annulare or sarcoidosis , secondary syphilis (not permanent, no swelling), plane warts , multiple leiomyomas, various adnexal tumours, and, pseudolymphoma.

Prevention & Therapy

None is required if no functional disturbance. Non-sedating antihistamines; H2 blockers or cromoglycate for gastrointestinal symptoms; PUVA; short-term high-potency topical glucocorticoids. Written information about the risk of anaphylaxis +/- adrenaline syringe in high risk cases.


Malignant transformation very rare.

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