Background Nodular melanoma (NM), representing 10-30% of all melanomas, plays a major role in global mortality related to melanoma. Nonetheless, the literature on dermoscopy of NM is scanty. Objectives To assess odds ratios (ORs) to quantify dermoscopic features of pigmented NM vs. pigmented superficial spreading melanoma (SSM), and pigmented nodular nonmelanocytic and benign melanocytic lesions. Methods To assess the presence or absence of global patterns and dermoscopic criteria, digitized images of 457 pigmented skin lesions from patients with a histopathological diagnosis of NM (n = 75), SSM (n = 93), and nodular nonmelanocytic and benign melanocytic lesions (n = 289; namely, 39 basal cell carcinomas, 85 seborrhoeic keratoses, 81 blue naevi, and 84 compound/dermal naevi) were retrospectively collected and blindly evaluated by three observers. Results Multivariate analysis showed that ulceration (OR 4·07), homogeneous disorganized pattern (OR 10·76), and homogeneous blue pigmented structureless areas (OR 2·37) were significantly independent prognostic factors for NM vs. SSM. Multivariate analysis of dermoscopic features of NM vs. nonmelanocytic and benign melanocytic lesions showed that the positive correlating features leading to a significantly increased risk of NM were asymmetric pigmentation (OR 6·70), blue-black pigmented areas (OR 7·15), homogeneous disorganized pattern (OR 9·62), a combination of polymorphous vessels and milky-red globules/areas (OR 23·65), and polymorphous vessels combined with homogeneous red areas (OR 33·88). Conclusions Dermoscopy may be helpful in improving the recognition of pigmented NM by revealing asymmetric pigmentation, blue-black pigmented areas, homogeneous disorganized pattern and abnormal vascular structures, including polymorphous vessels, milky-red globules/areas and homogeneous red areas. What's already known about this topic? Nodular melanoma (NM) often exhibits features associated with deep tumour extension and less commonly displays the classic dermoscopic features of superficial spreading melanoma (SSM). What does this study add? The study identifies dermoscopic features that are significantly associated with pigmented NM compared with pigmented SSM and nonmelanoma nodular lesions. This study validates, with a multivariate analysis, the dermoscopic features leading to a significantly increased likelihood of a diagnosis of pigmented NM.
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