Researchers from Timone Hospital, Aix-Marseille University, Marseille, France, and other institutions described evidence supporting that the “ugly duckling sign” is useful for experts and to a lesser degree to general population to spot the skin lesions with the highest probability of being melanoma (MM).
According to them, it is assumed that, in a given individual, variability of nevi is limited and represented by a few similarity clusters (SC) grouping all nevi sharing the same pattern, and that a nevus is suspicious when it does not fit with the SCs of the individual (UD).
To validate the concept of UD and SC, nine international experts (dermatologists) and nine novices (untrained individuals) were blindly tested, using digital images of the nevi at clinical and dermatoscopic scale, successively in 80 patients, (2,089 nevi and 7 MM).
Following data analysis, the researchers found that, at clinical scale, the experts had a better concordance for UDs (kappa 0.53, 0.33-0.87) and SCs (B-cubed 0.65, 0.55-0.73), than the novices (0.31, 0.03-0.51] and 0.56, 0.49-0.64, respectively). The experts identified a mean number of 1 UD and 2.7 SCs per patient, and agreed on consensual UD and SCs, whatever their natural propensity to see a high or a low number of UDs and SCs. Among the 254 nevi considered as UDs by at least 1 expert, 54 were considered as such by at least 5, and from them, 20 by all 9 experts. The 20 consensual UDs included all the MMs (7/7) (sensitivity for MM 100%). At the dermatoscopic scale, concordance tended to be lower for SCs than at clinical scale.