In a letter to the editor of Photodermatology, Photoimmunology & Photomedicine, researchers presented the case study of a pediatric patient with indolent systemic mastocytosis (SM) who was successfully treated with narrow-band ultraviolet B (UVB-NB) phototherapy for her cutaneous lesions. 

A 13-year-old-girl with a working diagnosis of maculopapular cutaneous mastocytosis presented with progressively worsening skin lesions. She complained of pruritus, and a physical examination revealed papules and erythematous macules distributed across her face, arms, and trunk. Darier’s sign was positive. 

Laboratory investigations revealed that her tryptase levels had doubled from 24 to 41.4 ng/mL. Skin biopsy revealed diffuse mast cell infiltrates; bone marrow biopsy demonstrated the presence of more than 15 mast cells. Flow cytometry indicated that the mast cells had coexpression of CD2, CD25, and CD117. Genetic testing revealed c-KIT D816V mutation. 

Her physicians revised her diagnosis to indolent SM and they initiated treatment with topical steroids and antihistamines. However, her symptoms remained poorly controlled, with negative psychological ramifications. 

Read more about SM etiology 

They decided to start her on UVB-NB twice a week. The initial dose was determined based on her skin type, and fluorescent UVB lamps with peak emissions at 311 to 313 nm were used. In view of the possibility of the massive degranulation of mast cells, a safer irradiation protocol was put in place. The phototherapy sessions were continued as long as no adverse events were noted, with the goal being the optimal control of cutaneous lesions and the alleviation of pruritus. 

Over 3 months, the patient underwent 30 treatments; the cumulative dose was 24.8 J/cm2. These sessions resulted in a complete resolution of her skin lesions and pruritus. Six years later, there has been no recurrence of any of these symptoms. 

“This case illustrates that UVB-NB phototherapy shows promising results and it could be considered as an important second-line therapy to treat cutaneous symptoms in pediatric mastocytosis patients, especially when other regimens have failed,” the authors concluded. 


Brazzelli V, Bossi G, Bonelli A, et al. A case of pediatric indolent systemic mastocytosis: the role of UVB-NB phototherapy in the treatment of cutaneous lesionsPhotodermatol Photoimmunol Photomed. Published online June 16, 2023. doi:10.1111/phpp.12894