Plaque-form urticaria pigmentosa

Plaque-form urticaria pigmentosa is a rare variant of cutaneous mastocytosis, a condition characterized by the abnormal accumulation of mast cells in the skin. In this specific form, mast cell infiltration presents as large, raised, brownish or reddish-brown plaques on the skin rather than the more typical small macules or papules seen in classic urticaria pigmentosa (also known as maculopapular cutaneous mastocytosis). The plaques may exhibit a positive Darier sign, meaning they become red, swollen, and itchy when rubbed or stroked due to the release of histamine and other mediators from the accumulated mast cells. This condition predominantly affects infants and young children, with onset typically occurring in the first months to years of life. The skin is the primary organ system affected, though systemic symptoms can occur due to mast cell mediator release, including flushing, itching (pruritus), and occasionally blistering in very young children. In most pediatric cases, the condition tends to improve spontaneously by adolescence or adulthood, though persistence into adulthood is possible. Treatment is primarily symptomatic and aimed at controlling mast cell mediator-related symptoms. First-line therapy includes oral antihistamines (both H1 and H2 receptor antagonists) to manage itching, flushing, and other histamine-mediated symptoms. Patients and caregivers are advised to avoid known mast cell degranulation triggers, such as extreme temperatures, vigorous skin friction, certain medications (e.g., NSAIDs, opioids), and emotional stress. Topical corticosteroids may be used for localized symptomatic relief. In more severe cases, mast cell stabilizers such as cromolyn sodium may be considered. Regular monitoring is recommended to assess for potential systemic involvement, particularly in cases that persist beyond childhood.

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