Amelanotic/hypomelanotic melanoma: clinical and dermoscopic features.

BACKGROUND: Amelanotic malignant melanoma is a subtype of cutaneous melanoma with little or no pigment on visual inspection. It may mimic benign and malignant variants of both melanocytic and nonmelanocytic lesions.
OBJECTIVES: To evaluate whether dermoscopy is also a useful technique for the diagnosis of amelanotic/hypomelanotic melanoma (AHM).
METHODS: We conducted a retrospective clinical study of 151 amelanotic/hypomelanotic skin lesions from 151 patients with a mean age of 47 years (+/- 17.5 SD). Digitized images of amelanotic/hypomelanotic skin lesions were converted to JPEG format and sent by e-mail from the five participating centres. Lesions included 55 amelanotic/hypomelanotic nonmelanocytic lesions (AHNML), 52 amelanotic/hypomelanotic benign melanocytic lesions (AHBML), and 44 AHM, 10 (23%) of which were nonpigmented, truly amelanotic melanomas (AM). The 44 AHM lesions were divided into thin melanomas (TnM) </= 1 mm (29 cases) and thick melanomas (TkM) > 1 mm (15 cases), according to the Breslow index. Five clinical features (elevation, ulceration, shape, borders and colour) as well as 10 dermoscopic criteria (pigment network, pigmentation, streaks, dots/globules, blue-whitish veil, regression structures, hypopigmentation, leaf-like areas, multiple grey-bluish globules, central white patch) and eight vascular patterns (comma, arborizing, hairpin, dotted, linear irregular, dotted and linear irregular vessels, and milky-red areas) were evaluated in order to achieve clinical and dermoscopic diagnoses. Statistical analyses were performed with the chi2-test and Fisher's exact test, when appropriate.
RESULTS: The most frequent and significant clinical features for TnM and TkM were asymmetry and ulceration (the latter only for TkM) compared with AHBML. 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 frequency of occurrence 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 associated with TnM and TkM were not found in our cases of AHBML and were only rarely seen in AHNML (3.6% and 1.8%, respectively). Moreover, TkM differed significantly from AHBML and TnM in frequency of occurrence of milky-red areas (93% vs. 17%; P </= 0.03 and 93% vs. 31%; P </= 0.01, respectively). The dermoscopic diagnosis of melanoma had a higher sensitivity and specificity than the clinical diagnosis (89% and 96% vs. 65% and 88%, respectively). With the limitation of the small number of cases, vascular patterns were the only dermoscopic criteria for 'truly' AM. In the 10 cases of 'truly' AM, we found milky-red areas in more than half of the cases (six of 10), dotted vessels in four, hairpin vessels in two, linear irregular vessels in two, dotted and linear irregular vessels in two.
CONCLUSIONS: Because dermoscopy uses criteria reflecting pigmentation (irregular pigmentation and irregular dots/globules) and vascular patterns, it is a useful technique not only for pigmented melanoma but also for hypomelanotic melanoma. In 'truly' AM, vascular patterns alone may not be sufficient to diagnose melanoma. A combined approach with the clinical information should help in the detection of 'truly' AM.