The "ugly duckling" sign: agreement between observers

To assess whether multiple observers can identify the same pigmented lesion(s) as being different from a patient's other moles ("ugly duckling" [UD] sign) and to explore whether the UD sign is sensitive for melanoma detection.

Baseline back images of 12 patients were obtained from a database of standardized patient images. All patients had at least 8 atypical moles on the back, and in 5 patients, one of the lesions was a histologically confirmed melanoma. The overview back images were supplemented with close-up clinical images of lesions. Participants were asked to evaluate whether the images showed any lesions on the back that differed from other nevi.

Dermatology clinic specializing in pigmented lesions.

Images were evaluated by 34 participants, including 8 pigmented lesion experts, 13 general dermatologists, 5 dermatology nurses, and 8 nonclinical medical staff.

A lesion was considered a generally apparent UD if it was perceived as different by at least two-thirds of the participants. Sensitivity was defined as the fraction of melanomas identified as different.

All 5 melanomas (100%) and only 3 of 140 benign lesions (2.1%) were generally apparent as different. The sensitivity of the UD sign for melanoma detection was 0.9 for the whole group, 1.0 for experts, 0.89 for general dermatologists, 0.88 for nurses, and 0.85 for nonclinicians. A limitation of the study is that assessment was done in virtual settings.

In the present study, melanomas were generally apparent as UDs. The potential of the UD sign for melanoma screening should be further assessed.