Amelanotic/hypomelanotic melanoma: clinical and Dermoscopic features

Abstract

Background Amelanotic malignant melanoma is a subtype of cutaneous melanoma with little or no pigment at visual inspection. Truly amelanotic melanomas are rare: often some pigmentation is present at the periphery of the lesions and the amelanotic/hypomelanotic melanoma (AHM) mimics benign and malignant variants of both melanocytic and non melanocytic lesions. We conducted a study to learn more about the clinical and the dermoscopic features of this melanoma and to investigate the possibility of differentiating it from amelanotic/hypomelanotic benign melanocytic lesions (AHBML) and from amelanotic/hypomelanotic non melanocytic lesions (AHNML). Methods Digitized images of 151 amelanotic/hypomelanotic skin lesions were sent by e-mail from participating centers. Lesions included 55 (AHNML), 52 (AHBML) and 44 AHM divided into thin melanomas (TnM) ≤1 mm (29 cases) and thick melanomas (TkM) >1 mm (15 cases), according to Breslow index. Clinical features and dermoscopic criteria were evaluated in order to achieve clinical and dermoscopic diagnosis. Results The most frequent and significant clinical features for TnM and TkM were asymmetry and ulceration (the latter only for TkM) compared with AHBML but these clinical features were also detected in AHNML without statistically significant differences in their frequency in the two groups. Irregular dots/globules (62% vs 35%; P≤0.03), regression structures (48% vs 27%; P≤0.03), irregular pigmentation (41% vs 11%; P≤0.03) and blue-whitish veil (10% vs 0%; P≤0.03) were the most relevant dermoscopic criteria for TnM in comparison with AHBML. TkM differed significantly from AHBML in the incidence of irregular pigmentation (87% vs 11%; P≤0.03), irregular dots/globules (73% vs 35%; P≤0.03), regression structures (67% vs 27%; P≤0.03), blue-whitish veil (27% vs 0%; P≤0.03) and hypopigmentation (13% vs 55%; P≤0.03). Linear irregular vessels and the combination of dotted and linear irregular vessels were associated with TnM and TkM but were not found in our cases of AHBML. The area under the curve for dermoscopic diagnosis was greater than the one for clinical diagnosis and dermoscopic diagnosis of melanoma had higher sensitivity and higher specificity than clinical diagnosis (89% and 96% vs 65% and 88% respectively). Conclusion Clinical features routinely used for diagnosing melanoma such as peripheral pigmentation, ulceration, and asymmetry, are not really helpful in diagnosing amelanotic/hypomelanotic melanomas. Because dermoscopy uses criteria reflecting both pigmentation (irregular pigmentation, and irregular dots/globules) and vascular patterns, it is a useful technique not only forffpigmented melanoma but also for amelanotic/hypomelanotic melanoma.