Dermoscopic island: a new descriptor for thin melanoma

To determine the frequency and the features of the dermoscopic island (DI) in melanocytic lesions and to assess its specificity for the diagnosis of melanoma. Dermoscopy improves the diagnostic accuracy of melanoma, but only a few dermoscopic descriptors specific for thin melanomas have been identified. We defined a new descriptor, the dermoscopic island, a well-circumscribed area showing a uniform dermoscopic pattern that differs from the rest of the pigmented lesion.

Dermoscopic images of 96 in situ melanomas, 266 invasive melanomas, and 612 dermoscopic atypical nevi were evaluated to establish the presence and the main pattern of the DI. Also, clinical and histologic characteristics were analyzed.

Dermoscopic images were collected from lesions excised between 2003 and 2008 at the Department of Dermatology, University of Modena and Reggio Emilia.

Specificity and odds ratio for melanoma; dermoscopic and histologic characteristics of lesions with a DI.

The DI was present in 10.4% of in situ melanomas, 4.1% of invasive melanomas, and 3.1% of dermoscopic atypical nevi. The odds ratio for melanoma was 1.922, and specificity was 96.9%. Invasive melanomas with a DI were thinner than those lacking this descriptor. In addition, more than half of the melanomas with a DI arose on a nevus. The DI appeared mainly reticular on a reticular background.

The DI is characteristic of thin melanoma arising in a nevus; thus, it can be considered a potential early sign of transformation of a nevus into a melanoma.