Nail matrix pigmented melanoma
In cases of melanonychia striata in a postpuberty patient, melanoma should be included in the differential diagnosis list. Clinical warning signs are adult onset, monodactylic involvement, changes over time observed by the patient, triangular shape of the band (indicating that the lesion is growing relatively faster than the nail plate), polychromia and the presence of pigmentation of the periungual skin (also known as Hutchinson’s sign). Dermoscopy provides useful additional information: the coloration of the background is light brown to black and the longitudinal dermoscopic micro-lines are irregular in their thickness, spacing and coloration and may show areas of parallelism disruption. Brown-to-black dots and globules may be observed in association with the longitudinal lines. Dermoscopic examination of periungual skin may disclose a micro Hutchinson’s sign invisible to the naked eye. In cases of prominent periungual pigmentation, its dermoscopical features either produce a parallel ridge pattern on the pulp, the lateral aspects and/or distal aspects of the finger/toe or a diffuse irregular pigmentation on the supramatricial skin. Careful attention must be paid to cases in which the irregular pattern of the lines is associated with subungual hemorrhage.
Nail matrix amelanotic melanoma
Amelanotic melanoma of the nail unit is very often a late presentation of the disease after several months/years of the undiagnosed condition which often includes typical monodactylic melanonychia striata. At this stage, partial or complete erosion of the nail plate is observed and the pigmentation that the patient eventually recalls having had has vanished, to be replaced by an often exophytic, ulcerative, bleeding tumor. Differential diagnosis includes pyogenic granuloma and several infectious conditions but, as a rule, amelanotic melanoma should be systematically included in cases of monodactylic nail plate erosion with or without nodular and erosive tumor. In this case, dermoscopy reveals features that have been described on amelanotic melanoma of the skin.
It shows an atypical vascular pattern characterized by the presence of linear and irregular vessels, the presence of milky-red areas or the presence of three or more types of vessel types within the same lesion. In a few cases, only red spots seen through the nail plate or in areas of plate erosion are visible. It is also possible to identify subtle areas of pigmentation, invisible to the naked eye and incorrectly but traditionally called “remnants” of pigmentation.
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