Possible role of dermoscopy in the detection of a primary cutaneous melanoma of unknown origin.

For 2-8% of patients with metastatic melanoma, cutaneous and mucosal clinical examination does not lead to diagnosis of the primary tumour, which remains unknown. We report the case of a 41-year-old male patient who had received a diagnosis of metastatic melanoma after histological examination of an enlarged axillary lymph node, without previous detection of the primary lesion at his first dermatological examination. No pigmented skin lesions located in the anatomical area potentially drained by the affected axillary basin showed clinical features suggestive of a melanoma. Neither did the so-called 'ugly duckling' sign help us to identify the melanoma, because of the presence of a large number of clinically similar, common or slightly atypical melanocytic lesions located in that area. After dermoscopic examination we were able to narrow the field of possible candidates for excision to four lesions, selected on the basis of their dermoscopic features. Histological examination revealed the primary melanoma (superficial spreading melanoma (SSM), level III, thickness 0.5 mm)--located on the back--and three naevi with atypia. Preoperative distinction of the melanoma from the other three lesions was not possible because of the lack of well-established features of malignancy, even at dermoscopic analysis ('featureless' melanoma). Dermoscopy may thus play a role in the detection of a clinically unknown primary melanoma by narrowing the field of lesions to be removed for histological examination, saving many unnecessary excisions that would otherwise be inevitable.