Luc Thomas and Sandra Ronger
Dermoscopy equipment Semiological patterns Diagnosis Further reading
Diagnosis of melanonychia striata is one of the most difficult aspects of clinical dermatology. Melanoma is feared in most situations; however, melanoma of the nail apparatus is rare (about 1 % of all cutaneous melanomas). The clinical presentation of early nail apparatus melanoma—longitudinal pigmentation—is shared by many other clinical processes with much more favourable outcomes, such as nail apparatus naevus or lentigo, drug-induced pigmentation, subungual haemorrhage and ethnic-type nail pigmentation. The 'gold standard' of diagnosis remains the pathological examination of the nail matrix biopsy, but the biopsy procedure is usually painful and often results in nail dystrophy.
Clinical criteria have been defined in an attempt to discriminate between suspect lesions that should undergo nail apparatus biopsy and less suspect ones that can just be followed-up. Suspicious signs are the occurrence of the pigmentation during adulthood, monodactlylic location of the pigmentation, heterogeneity of the pigmentation, and its progressive enlargement. Lesions more likely to be benign are those present since childhood, multiple lesions on several fingers and toes, and stable and homogeneously coloured lesions.
Dermoscopy provides additional evidence on which to base the decision to proceed with nail apparatus biopsy. This chapter describes the different patterns observed on epiluminescence microscopy and their relevance in the differential diagnosis of a nail pigmentation. Dermoscopy can also be used in the diagnosis of other nail conditions, for example the observation of vascular abnormalities associated with scleroderma or systemic lupus erythematosus.
Dermoscopy on nails can be performed using any type of hand-held dermoscope. After trying different compounds the authors have adopted a clear antiseptic gel (Purell, Gojo Industries Inc., Akron, Ohio, USA) for immersion, but ultrasonography gel may also be used provided it is not coloured. All the pictures in this chapter have been taken with a standard dermoscopic camera (Heine Dermaphot, Herrshing, Germany).
On the basis of a prospective study of 148 cases of linear nail pigmentation we have identified seven different semiological patterns:
1 Blood spots: these spots are characterized by a homogeneous colour. Recently formed lesions are purple and round; they turn brown and develop a more linear pattern with time. In older lesions the proximal edge of the spot remains sharply demarcated with an ovoid or polycyclic proximal border, while the distal edge appears elongated with creation of a somewhat filamentous pattern (see Figures 12.11, 12.12).
2 Brown background: in this pattern, usually associated with regular or irregular lines, the background of the area corresponding to the pigmented band appears homogeneously brown (Figures 12.1-12.6).
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