Nodular urticaria pigmentosa

Nodular urticaria pigmentosa is a rare subtype of cutaneous mastocytosis, a condition characterized by the abnormal accumulation of mast cells in the skin. Also known as nodular mastocytosis, this form presents with distinctive large nodular or tumor-like lesions on the skin, rather than the more typical small macules or papules seen in classic urticaria pigmentosa (maculopapular cutaneous mastocytosis). The nodules are typically reddish-brown or yellowish in color and may blister or urticate (develop hive-like reactions) when rubbed or irritated, a clinical sign known as the Darier sign. This form predominantly affects infants and young children, often appearing within the first months of life. The disease primarily affects the skin, but mast cell degranulation can cause systemic symptoms including flushing, itching (pruritus), and occasionally gastrointestinal symptoms such as diarrhea or abdominal pain. In severe cases, particularly when large nodular lesions are present, extensive mast cell degranulation can rarely lead to hypotension or anaphylactoid reactions. The prognosis for nodular urticaria pigmentosa in children is generally favorable, as many cases spontaneously resolve or significantly improve by puberty. Treatment is primarily symptomatic and includes avoidance of triggers that cause mast cell degranulation (such as physical stimuli, temperature extremes, and certain medications), antihistamines (both H1 and H2 receptor blockers) to control itching and flushing, and topical corticosteroids for localized symptoms. Epinephrine auto-injectors may be prescribed for patients at risk of severe systemic reactions. Regular monitoring is recommended to assess for potential systemic involvement, although progression to systemic mastocytosis is uncommon in pediatric cases.

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