Management of Poorly Controlled Indolent Systemic Mastocytosis Using Narrowband UVB Phototherapy

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The mastocytoses comprise a group of proliferative stem cell disorders defined by the abnormal accumulation of mast cells (MCs) in the skin or other body tissues including the bone marrow, gastrointestinal tract, and liver. Systemic mastocytosis is defined by the presence of one major and one minor criterion or 3 minor criteria delineated by the World Health Organization (WHO). We present the case of a 57-year-old woman with a 10-year history of red-brown pruritic maculopapular lesions on the upper and lower extremities and trunk who was originally diagnosed with cutaneous mastocytosis. Symptoms had been adequately controlled with a combination of topical corticosteroids and antihistamines. After 9 years of controlled disease, the patient presented with increasingly severe breakthrough pruritus and new skin lesions on the head and neck. Further workup included bone marrow biopsy, which demonstrated dense mastocyte infiltrates without evidence of functional impairment, and elevated serum tryptase levels. Narrowband UVB (NB-UVB) phototherapy was initiated, and after 20 treatments the patient reported a marked decrease in symptoms. This case provides evidence of the efficacy of NB-UVB phototherapy in managing patients with long-standing indolent systemic mastocytosis (ISM) who have stopped responding adequately to topical corticosteroids and antihistamines.