NB-UVB (311-312 nm)-induced lentigines in patients with mycosis fungoides: a new adverse effect of phototherapy.

Background: Lentigines are a common pigmentary disorder in adults and in patients treated by psoralen and ultraviolet A (PUVA) radiation. Their appearance following treatment with narrow-band ultraviolet B (NB-UVB) radiation has been reported in only two patients.
Objective: To describe the clinical and histological features of NB-UVB-induced lentigines their relation to dosimetry and the course of the eruption in patients with mycosis fungoides (MF).
Methods: The files of all patients with MF treated in our department in 2003-2010 were searched to identify those in whom lentigines appeared following monotherapy with NB-UVB radiation.
Results: Of the 73 patients with early stage MF identified, 10 met the study criteria. Lentigines were detected in skin previously involved by MF in seven patients, and in both involved and uninvolved skin in three patients. They appeared during therapy in three patients, after a mean of 56 exposures (range 50-61), and several months (mean 7.8) following completion of treatment in seven patients, after a mean of 69 exposures (range 32-157). Histopathological study of lesions from five patients revealed basal hyperpigmentation relative to adjacent normal-looking skin. Two lesions had a slight increased number of normal-looking melanocytes on immunohistochemical staining with melanoma cocktail. One lesion had elongated rete ridges. The lesions persisted throughout follow-up (mean 26.7 months) in 8 patients.
Conclusions: Patients with MF treated with NB-UVB may acquire lentigines. As opposed to PUVA-induced lentigines which are a known common side-effect of long-term treatment, NB-UVB-induced lentigines are uncommon but appear earlier, even after a few months of treatment.
(© 2011 The Authors. Journal of the European Academy of Dermatology and Venereology © 2011 European Academy of Dermatology and Venereology.)