Unusual Urticaria Pigmentosa in an Asian Man With Indolent Systemic Mastocytosis: A Case Report

Background: The diagnosis of mastocytosis remains challenging. Given that the disease has a low prevalence and its clinical presentations range from asymptomatic to severe life-threatening conditions, physicians’ lack of awareness of mastocytosis is the main barrier to its diagnosis. Skin involvement is common. In adults, skin lesions are highly suggestive of systemic mastocytosis; however, clinical demonstration of lesions is difficult if they are minimal in number. In Asian, who had dark brown skin color, urticaria pigmentosa was not easy to identify. Here we present the case of indolent systemic mastocytosis with an unusual urticaria pigmentosa. Case presentation: A 48-year-old man had had recurrent severe honeybee anaphylaxis since he was 23. He had small, subtle, brownish skin lesions on his chest and abdomen, which he and previous physicians had not recognized. The skin lesions were compatible with urticaria pigmentosa, also known as maculopapular cutaneous mastocytosis. His clinical findings and an elevated baseline tryptase level triggered a thorough systemic mastocytosis investigation. The skin and bone marrow were infiltrated by abnormal, spindle-shaped mast cells, and KIT and TET2 mutations were in the patient’s serum. The honeybee anaphylaxis mechanism in this patient was IgE mediated, supported by a positive result of specific IgE to honeybee. The final diagnosis was indolent systemic mastocytosis with IgE-mediated honeybee anaphylaxis. As venom immunotherapy is unavailable in Thailand, we prescribed treatment with a regular, oral, nonsedating H1-antihistamine and an epinephrine self-injector. At the 2-year follow-up, the patient had not progressed to advanced systemic mastocytosis nor experienced any anaphylactic episodes.Conclusion: Urticaria pigmentosa is a small, round, brown, or red maculopapular lesion. In the Asian population with dark brown skin color, physician should be exclusively careful examination, particularly in a hidden area and in anaphylaxis cases. Early recognition of urticaria pigmentosa in the adult patient might reduce the delay in diagnosis of indolent systemic mastocytosis.