Typical urticaria pigmentosa

Typical urticaria pigmentosa (UP), also known as maculopapular cutaneous mastocytosis (MPCM), is the most common form of cutaneous mastocytosis. It is characterized by an abnormal accumulation of mast cells in the skin, leading to the development of multiple reddish-brown to yellowish-brown macules and papules that can appear anywhere on the body, though they most commonly affect the trunk and extremities. A hallmark clinical feature is Darier's sign, in which stroking or rubbing an affected lesion causes localized urticaria (hiving), redness, and swelling due to the release of histamine and other mediators from the accumulated mast cells. The condition primarily affects the skin (integumentary system), but mast cell mediator release can also cause systemic symptoms including flushing, itching (pruritus), abdominal discomfort, and occasionally diarrhea. In children, typical urticaria pigmentosa usually presents in infancy or early childhood and often improves or resolves spontaneously by puberty. In adults, the condition tends to be more persistent and may occasionally be associated with systemic mastocytosis, warranting further investigation including serum tryptase levels and, in some cases, bone marrow biopsy. Treatment is primarily symptomatic and aimed at controlling mast cell mediator-related symptoms. First-line therapy includes H1 and H2 antihistamines to manage itching, flushing, and gastrointestinal symptoms. Patients are advised to avoid known mast cell degranulation triggers such as extreme temperatures, vigorous rubbing of the skin, certain medications (e.g., NSAIDs, opioids), alcohol, and emotional stress. Topical corticosteroids or calcineurin inhibitors may be used for localized skin symptoms. In more severe cases, oral cromolyn sodium, leukotriene receptor antagonists, or omalizumab may be considered. Patients should carry emergency epinephrine if they are at risk for anaphylaxis.

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