Exposure to UV radiation is linked to the development of nevi, and studies suggest that sunburns during childhood may be an independent risk factor for malignant melanoma. Recognition of changes in melanocytic nevi is important, and dermoscopy (magnification of the skin) has become a routine clinical method of examining these lesions. Because UV exposure can cause clinical, histologic and ultrastructural changes in melanocytic nevi, Hofmann-Wellenhof and associates investigated whether exposure to two minimal erythema doses of UV radiation induces changes in the dermoscopic evaluation of melanocytic nevi.
Four volunteers with a total of 15 melanocytic nevi participated in the study. Each nevus and 2 cm of adjacent skin were exposed to two minimal erythema doses of UV radiation. The lesions were then examined for differences in their dermoscopic appearance after exposure. The nevi were graded before the UV exposure and again three, seven, 14 and 28 days after exposure using a visual analog scale.
Three days after UV irradiation, the borders of the nevi were more faded, the nevi were more darkly pigmented and the hypopigmented areas were significantly less prominent. The pigment network structures were less prominent and more faded. No significant changes were noted in asymmetry, erythema in the nevus, telangiectasia, regularity of pigment network or presence of brown-black globules.
The changes in the magnified images were most prominent on the seventh day. The borders of the nevi were more faded, more dark pigmentation was present and hypopigmented areas were significantly less prominent. The number and intensity of the brown-black globules were increased.
On the 14th day after UV irradiation, the nevi were still darker brown, and hypopigmented areas were fading. On the 28th day, only the hypopigmented areas were still less prominent than before UV irradiation.
It is likely that the increase in pigmentation and in brown-black globules reflect induction of melanin synthesis. The changes observed in the nevi are in accordance with histopathologic findings of nevi excised in summer months, when sun exposure is maximal.
Dermoscopic evidence of an increase in brown-black globules and darkening of pigmentation in melanocytic nevi has been cited by some authors as a sign of malignant melanoma. Even with the use of × 10 magnification, the black-brown globules are sometimes indistinguishable from the black dots that are one of the most specific dermoscopic criteria for melanoma. In contrast, a faded border, discrete pigment network, low amount of hypopigmented area and regularity of pigment network are considered to be dermoscopic criteria for benign nevi.
The authors conclude that low-dose UV radiation, such as that occurring with a sunburn, can induce transient changes in melanocytic nevi. These changes are primarily due to increased pigmentation. Although many of the changes observed in the nevi may be clinically interpreted as benign, the hyperpigmentary changes may be misidentified as malignant melanoma. Because of this possibility, the authors recommend that melanocytic nevi in patients with a recent history of sunburn be reexamined one month later to assure accurate diagnosis and avoid unnecessary biopsy.