Critical effects of intense sun exposure on the expression of epiluminescence microscopy features of acquired melanocytic nevi

Background: Current knowledge of the histologic counterparts of epiluminescence microscopy (ELM) features in pigmented skin lesions is limited. As a particular aspect of this problem, the transient effects of intense sun exposure on the morphological characteristics of melanocytic nevi may influence the expression of ELM features as well as the demonstration of stable and consistent histologic correlates. Observations: Forty melanocytic nevi from 11 subjects living in Northern Italy were examined by digital ELM before and after 5 to 13 days of sun exposure at latitudes of 5 degrees north to 3 degrees south. A number of multifaceted changes were observed. In particular, 3 lesions showed the expression of some structures compatible with radial streaming, pseudopods, and gray-blue areas. These features are considered to have often severe histologic correlates. In a third image, obtained 5 to 6 weeks later, they showed partial or total regression. Another case showed a massive regression of the pigment network as a result of a progressive inflammatory reaction with marked asymmetry in the distribution of pigmentation. Conclusions. Digital ELM has the potential to detect subtle changes in the structure of nevi after intense sun exposure. The transient observation of certain ELM features often associated with severe histologic substrates casts doubts on the ability of ELM to characterize sun-exposed nevi by a single examination.