By Gary M. White, MD
Urticaria pigmentosa (UP) is a variant of cutaneous mastocytosis in which multiple pigmented macules or papules develop, each overlying a dermal accumulation of mastocytes.
Various patterns of cutaneous mastocytosis occur in children. One extensive review [BJD 2015;172;642] of all cases of pediatric mastocytosis found the following distribution of clinical presentation:
|Diffuse cutaneous mastocytosis||5%|
Patients may have a few to several thousand brown macules or papules. The trunk is the most common site, followed by the extremities. The face, scalp, palms, and soles are usually spared. Both children and adults may be affected. Gastrointestinal or systemic histamine effects include diarrhea, stomach pain, flushing, or lightheadedness.
Darier sign (urtication upon stroking) is positive. Adult patients who have presented with typical urticaria pigmentosa may go on to develop systemic mastocytosis as manifested by nodules, flushing, hepatosplenomegaly, and duodenal ulcers. Death secondary to anaphylaxis has been reported in a patient who drank alcohol and then was exposed to winter snow. The pigmentation histologically is basal melanosis. Histamine in vitro stimulates melanocytes suggesting the mechanism of pigmentation. Massive peripheral eosinophilia may rarely be seen [PD 1997;14;284].
All patients should have a CBC with differential. Tryptase levels may be measured and may correlate with extent of skin involvement. Bone survey and bone marrow biopsy often shows abnormalities but their significance is unclear. KIT mutation analysis may be considered in an investigational setting.
Any patient with a history of anaphylactic symptoms should carry epinephrine. The CBC should be followed periodically. Certain agents can cause mast cell degranulation and should be avoided. Dextromethorphan, which is related to codeine, can degranulate mast cells and can be found in over-the-counter cough syrups for children [PD 1996;13;410]. Betamethasone dipropionate ointment occluded for 6 days caused near-complete resolution in one study. Antihistamines may be taken routinely for patients who are symptomatic. For abdominal pain or other GI symptoms, cromylyn 200 mg. QID (for kids 100 mg. QID) can be very effective.
For adults, see adult, diffuse mastocytosis.
Childhood UP usually remits spontaneously over time.
UP and a congenital nevus.
Papular lesions and Darier sign.
UP in a younger child.
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