Cutaneous mastocytosis presenting as urticaria pigmentosa with prominent bone involvement: A case report

Mastocytosis comprises a rare group of disorders characterized by the accumulation of mast cells, primarily in the skin and/or internal organs. Cutaneous mastocytosis includes maculopapular cutaneous mastocytosis (urticaria pigmentosa), diffuse cutaneous mastocytosis, and cutaneous mastocytoma, with urticaria pigmentosa representing the most frequent clinical variant. It typically presents as erythematous to brownish macules or papules, often associated with pruritus.
We report the case of a 48-year-old woman with a history of rheumatologic and cardiac disease, who presented with multiple disseminated, well-demarcated, livid-brown, mildly pruritic macules involving the trunk and extremities. Skin biopsy revealed a perivascular mastocytic inflammatory infiltrate, with immunohistochemistry strongly positive for CD117, confirming the diagnosis of cutaneous mastocytosis. Serum tryptase levels were within normal limits. Systemic evaluation revealed skeletal involvement, including femoral osteopenia and vertebral osteoporosis.
The patient was managed with lifestyle and dietary modifications aimed at avoiding known triggers, in addition to H1-antihistamine therapy, resulting in good functional improvement.
This case is of interest due to its presentation in adulthood with systemic skeletal involvement despite normal serum tryptase levels, highlighting the importance of comprehensive evaluation even in apparently indolent cutaneous forms. It also underscores potential limitations, including the absence of KIT mutation analysis and bone marrow biopsy, which could further refine disease classification and prognostic assessment.