Figures 1 & 2. A vitiligo patient before and after NB-UVB treatment. Images courtesy of Pearl E Grimes, MD.

Vitiligo is a common skin depigmentation disorder in which the melanocytes, the skin cells which produce melanin pigment, are progressively lost. Clinically, when vitiliginous lesions (the ‘patches’ of skin which have lost their pigment) are repeatedly exposed to an intensive dose of narrowband UVB radiation (308 or 311-313nm), it is common to see small spots, sometimes described as ‘freckles’ or  ‘islands’, of repigmentation forming within the lesion. This occurs because the melanocytes producing this melanin have developed from stem cells reserved in the bulge region of the hair follicle, known as the niche. Their development is stimulated by NB-UVB and they migrate to the skin directly surrounding the hair follicle from which they were derived. As the melanocytes continue to travel through the skin and produce melanin, these ‘islands’ begin to spread and merge, eventually creating broader, but seldom perfect, repigmentation in the treated area (see Figures 1 & 2). (more…)